The main aim was to examine the load bearing of individual hamstring muscles in different contraction types and intensities, through local stiffness measurement by shear wave elastography (SWE). A secondary aim was to examine the relationship between the SWE stiffness measure and hamstrings morphology. Ten healthy males (age 22.1±4.1 years; height 173.7±5.9 cm; body mass 68.6±12.4 kg; mean ± SD) performed knee flexions on an isokinetic dynamometer at different intensities (20-70%MVC, random order) in three separate, randomized conditions: isometric (ISO), concentric (CON) and eccentric (ECC). SWE was used to measure muscle shear wave velocity (SWV) in biceps femoris long head (BFlh), semitendinosus (ST) and semimembranosus (SM) during contraction. Muscle anatomical cross-sectional area (ACSA) was measured with magnetic resonance imaging and muscle architecture with B-mode ultrasonography. Muscle SWV increased linearly with contraction intensity, but at a varying rate among muscles and contraction types. ST exhibited greater SWV than BFlh and SM in all contraction types, however, there was an upward shift in the SM SWV-torque relationship in ECC compared to ISO and CON. Strong negative correlations were found between peak ISO SWV and ST ACSA (r = -0.81, p = 0.005) and BFlh pennation angle (r = -0.75, p = 0.012). These results suggest that ST has a primary role in hamstrings load bearing in all contraction types, likely due to its morphology; however, there is evidence of increased contribution from SM in eccentric muscle actions.

<title>Abstract</title>Human steady-state locomotion modes are symmetrical, leading to symmetric mechanical function of human feet in general; however, track distance running in a counterclockwise direction exposes the runner’s feet to asymmetrical stress. This may induce asymmetrical adaptation in the runners’ foot arch functions, but this has not been experimentally tested. Here, we show that the plantar fascia (PF), a primary structure of the foot arch elasticity, is stiffer for the left than the right foot as a characteristic of runners, via a cross-sectional study on 10 track distance runners and 10 untrained individuals. Shear wave velocity (index of tissue stiffness: SWV) and thickness of PF and foot dimensions were compared between sides and groups. Runners showed higher PF SWV in their left (9.4 ± 1.0 m/s) than right (8.9 ± 0.9 m/s) feet, whereas untrained individuals showed no bilateral differences (8.5 ± 1.5 m/s and 8.6 ± 1.7 m/s, respectively). Additionally, runners showed higher left to right (L/R) ratio of PF SWV than untrained men (105.1% and 97.7%, respectively). PF thickness and foot dimensions were not significantly different between sides or groups. These results demonstrate stiffer PF in the left feet of runners, which may reflect adaptation to their running-specific training that involves asymmetrical mechanical loading.

This study aimed to identify characteristics of the triceps surae muscles and aponeuroses stiffness in vivo, during graded isometric submaximal plantarflexion efforts. A total of twelve healthy male subjects (age: 27 ± 4 years) participated and were required to stay at rest (0% MVC) and perform isometric submaximal plantar flexion contractions (20%, 40%, 60% of MVC) on a dynamometer. Young's modulus of triceps surae muscles and the adjoining aponeuroses between gastrocnemii and soleus at the proximal and distal sites were obtained in the longitudinal direction (along muscle's line of action) during at rest and submaximal plantar flexions. Additionally, Young's modulus of adjoining aponeuroses in the transverse direction at the distal sites was also calculated. Young's modulus of LG (lateral gastrocnemius), SOL-lat (lateral part of soleus) and LPS (superficial aponeurosis of LG) at the proximal site showed significant (p < 0.001) graded increase response to the submaximal contraction levels. Besides, in the lateral side, significant differences in the Young's modulus of aponeuroses were observed between longitudinal and transverse directions at rest and during contractions (p < 0.002). Changes of aponeuroses length were significantly correlated with Young's modulus changes of the proximal gastrocnemii muscle bellies (r = 0.43-0.45, p = 0.006-0.008) and superficial aponeuroses (r = 0.49-0.60, p < 0.002). The results further indicate that the triceps surae muscles and aponeuroses showed inhomogeneous and anisotropic mechanical properties during submaximal muscle contractions, and the stiffening effect of muscle belly possibly make influence on the mechanical properties of aponeuroses during muscle contractions, especially for the lateral gastrocnemius.

The purpose of this study was to investigate the site- and sex-differences in the morphological and mechanical properties of the plantar fascia (PF) in humans. The thickness and shear wave velocity (SWV) of PF at five different sites between the medial calcaneal tubercle and the second toe were measured for 40 healthy young participants (20 males and 20 females) using supersonic shear imaging (SSI). The thickness and SWV measurements were highly repeatable (ICC ≥ 0.93). The proximal sites of PF around the calcaneal attachment were significantly thicker and stiffer (higher SWV values) than the middle and distal sites (p < 0.05). In addition, females had significantly thinner PF in proximal and middle sites than males, while being significantly stiffer in regardless of the sites, compared with males (p < 0.05). The results of the present study partly support previous findings on the site- and sex-differences in PF morphology, and further reveal inhomogeneity and sex-specificity of PF stiffness. The present study widely opens the possibility of evaluating PF functions in vivo.

The human triceps surae (two gastrocnemii and soleus) has aponeuroses in the proximal and distal aspects, the latter of which insert into the calcaneus by sharing the common Achilles tendon. These tendinous tissues are known to have elasticity and upon muscle contraction the aponeurosis is stretched both longitudinally (along the muscle's line of action) and transversely. Higher aponeurosis transverse deformability has been documented, but there is a paucity of information on the morphology and mechanical properties of human aponeurosis. This study aimed to identify morphological and mechanical characteristics of the human triceps surae aponeuroses. Twenty-five triceps surae muscle-tendon units were procured from 13 human donors (formalin fixed, 6 males, 7 females) aged 67-91 years. Specimens of aponeuroses were excised from the eight regions (posterior and anterior regions of the gastrocnemius medialis and lateralis, medial and lateral parts of soleus; proximal, middle, and distal sites each, 2-4 cm × 2-4 cm). Aponeurosis thickness was measured using a digital caliper. Uniaxial tensile tests were implemented to determine the mechanical properties of specimens loaded longitudinally (along the muscle's line of action) and transversely. The aponeurosis thickness showed significant differences between muscles and sites, while Young's modulus showed direction-dependent (longitudinal vs. transverse) differences within sites. Results show different morphology and mechanical properties of aponeuroses between synergist muscles. The reason for site-dependent differences in stiffness is due to a reduced aponeurosis thickness rather than a reduction in the material property. The anisotropic elastic feature (differences between longitudinal and transverse directions) of the aponeuroses was more pronounced than previous in vivo findings, suggesting inherent material design of the aponeurosis that matches three-dimensional contractile behavior of muscle fibers.

Bioelectrical impedance spectroscopy (BIS) can assess intracellular water (ICW) and total water (TW) in limbs. This study aimed to examine whether BIS can explain a part of the inter-individual variation of the muscle size-strength relationship in older adults. We analyzed the data of 79 participants aged 64-86 years. The maximal voluntary isometric torques of dorsiflexion and plantar flexion on the right side were measured. The anterior and posterior muscle thickness (MT) in the right lower leg was assessed using ultrasonography. The length of the right lower leg (L) was measured, and the ICW-to-TW ratio (ICW/TW) in the right lower leg was obtained using BIS. The MT was multiplied by L to represent an index of muscle volume (MV). Correlation and stepwise regression analyses were performed. The anterior and posterior MT × L significantly and positively correlated with the muscle torque of dorsiflexion and plantar flexion (r = 0.710 and 0.649, respectively, P < 0.001). In the stepwise regression analyses, ICW/TW was selected as a significant predictor of muscle torque independent of MT × L (P < 0.05) for both dorsiflexion and plantar flexion. Electrical parameters of BIS (membrane capacitance, characteristics frequency, and phase angle) in the lower leg also significantly correlated with muscle torques. In addition, the skeletal muscle mass index (appendicular lean mass/height2) was also associated with ICW/TW (P < 0.001). The present results suggest that ICW/TW explains the interindividual variations of the muscle size-strength relationship.

The whole thigh muscles are covered with the fascia lata, which could have morphological and mechanical features that match the underlying muscles' functions. In this study, we investigated the morphological and elastic properties of the human fascia lata taken from four (anterior, medial, lateral, and posterior) sites on the thigh of 17 legs of 12 cadavers (6 males and 6 females, 75-92 years). The thickness of the fascia lata was determined with a caliper. The interwoven collagen fiber's directions were measured and classified into longitudinal, transverse, and diagonal in two opposing directions, relative to the thigh. Tensile strength test along the longitudinal and transverse directions was performed, and the stiffness, Young's modulus, and hysteresis were determined. Fascia lata at the lateral site (0.8 ± 0.2 mm) was significantly thicker compared to other sites (0.2-0.3 mm). Fiber's directions showed substantial variability among sites, and longitudinally directed fibers were higher in proportion (28-32%) than those in other directions (20-27%) at all sites except for the posterior site. The stiffness and Young's modulus in the longitudinal direction (20-283 N/mm; 71.6-275.9 MPa, highest at the lateral site) were significantly higher than in the transverse direction (3-16 N/mm; 3.2-41.9 MPa, lowest at the lateral site). At the medial site, the proportion of the transversely directed fibers was higher in females than males, with higher stiffness and Young's modulus thereof. The present study shows that the fascia lata possesses site- and gender-dependence of the morphological characteristics and elastic properties.

We recently reported that wearing unstable rocker shoes (Masai Barefoot Technology: MBT) may enhance recovery from marathon race-induced fatigue. However, this earlier study only utilized a questionnaire. In this study, we evaluated MBT utilizing objective physiological measures of recovery from marathon-induced muscle damages. Twenty-five university student novice runners were divided into two groups. After running a full marathon, one group wore MBT shoes (MBT group), and the control group (CON) wore ordinary shoes daily for 1 week following the race. We measured maximal isometric joint torque, muscle hardness (real time tissue elastography of the strain ratio) in the lower limb muscles before, immediately after, and 1, 3, and 8 days following the marathon. We calculated the magnitude of recovery by observing the difference in each value between the first measurement and the latter measurements. Results showed that isometric torques in knee flexion recovered at the first day after the race in the MBT group while it did not recover even at the eighth day in the CON group. Muscle hardness in the gastrocnemius and vastus lateralis showed enhanced recovery in the MBT group in comparison with the CON group. Also for muscle hardness in the tibialis anterior and biceps femoris, the timing of recovery was delayed in the CON group. In conclusion, wearing MBT shoes enhanced recovery in lower leg and thigh muscles from muscle damage induced by marathon running.

Many extant studies proposed various stabilizing control methods for humanoids during the stance phase while hopping and running. Although these methods contribute to stability during hopping and running, humanoid robots do not swing their legs rapidly during the flight phase to prevent rotation in the yaw direction. Humans utilize their torsos and arms when running to compensate for the angular momentum in the yaw direction generated by leg movement during the flight phase. In this study, we developed an angular momentum control method based on human motion for a humanoid upper body. The method involves calculation of the angular momentum generated by the movement of the humanoid legs and calculation of the torso and arm motions required to compensate for the angular momentum of the legs in the yaw direction. We also developed a humanoid upper-body mechanism having human link length and mass properties, using carbon-fiber-reinforced plastic and a symmetric structure for generating large angular momentum. The humanoid robot developed in this study could generate almost the same angular momentum as that of a human. Furthermore, when suspended in midair, the humanoid robot achieved angular momentum compensation in the yaw direction.

Purpose: This study aimed to elucidate growth pattern of mechanical properties of the Achilles tendon and to examine if imbalance between growth of bone and muscle–tendon unit occurs during adolescence. Methods: Fourteen elementary school boys, 30 junior high school boys, 20 high school boys and 15 male adults participated in this study. Based on estimated age at peak height velocity (PHV), junior high school boys were separated into two groups (before or after PHV). An ultrasonography technique was used to determine the length, cross-sectional area, stiffness and Young’s modulus of Achilles tendon. In addition, the maximum strain in “toe region” (strainTP) was determined to describe the balance between growth of bone and muscle–tendon unit. Results: No group difference was observed in length, cross-sectional area and strainTP among the groups. However, stiffness and Young’s modulus in after PHV groups were significantly higher than those of elementary school boys and before PHV groups (p ≤ 0.05). Conclusions: These results indicate that mechanical properties of Achilles tendon change dramatically at and/or around PHV to increased stiffness. The widely believed assumption that muscle–tendon unit is passively stretched due to rapid bone growth in adolescence is not supported.

This study examined localization of muscle damage within the quadriceps femoris induced by different types of eccentric exercises by using transverse relaxation time (T2)-weighted magnetic resonance imaging (MRI). Thirty-three young males performed either of the following three exercises: single-joint eccentric contraction of the knee extensors (KE), eccentric squat (S), or downhill walking (DW) (n=11/exercise). KE and S consisted of 5-set×10-lowering of 90% one-repetition maximum load. DW was performed for 60 minutes with −10% slope, 6 km/h velocity, and 20% body mass load carried. At pre- and 24-, 48-, and 72-hours post-exercise, T2-MRI was scanned and T2 values for the rectus femoris (RF), vastus intermedius (VI), vastus lateralis (VL), and vastus medialis (VM) at proximal, middle, and distal sites were calculated. Additionally, soreness felt when static pressure was applied to these sites and maximal isometric knee extension torque were measured. Maximal torque significantly (P&lt
.05) decreased (7%-15%) at 24-48 hours after all exercises. T2 significantly increased (3%-9%) at 24-72 hours after all exercises, with heterogeneities within the muscles found in each exercise. Effect size and peak change of T2, as well as soreness, overall indicated that the proximal RF after KE and middle VM after S and DW were most affected by these exercises. The VL did not show any significant T2 increase after all exercises. These results suggest that muscle damage specifically localizes at the proximal RF by KE and at the middle VM by S and DW, while the VL is least damaged regardless of the exercises.

This study tested the hypothesis that the effect of hip joint angle on concentric knee extension torque depends on knee joint angle during a single knee extension task. Twelve men performed concentric knee extensions in fully extended and 80 degrees flexed hip positions with maximal effort. The angular velocities were set at 30 degrees s(-1) and 180 degrees s(-1). The peak torque and torques attained at 30 degrees, 50 degrees, 70 degrees and 90 degrees (anatomical position= 0 degrees) of the knee joint were compared between the two hip positions. Muscle activations of the vastus lateralis, medialis, rectus femoris and biceps femoris were determined using surface electromyography. The peak torque was significantly greater in the flexed than in the extended hip position irrespective of angular velocity. The torques at 70 degrees and 90 degrees of the knee joint at both angular velocities and at 50 degrees at 180 degrees s(-1) were significantly greater in the flexed than in the extended hip position, whereas corresponding differences were not found at 30 degrees (at either angular velocity) and 50 degrees (at 30 degrees s(-1)) of the knee joint. No effect of hip position on muscle activation was observed in any muscle. These results supported our hypothesis and may be related to the force-length and force-velocity characteristics of the rectus femoris.

Knee alignment is suggested to be a factor affecting each quadriceps femoris muscle size, and knee alignment such as Q-angle differs between men and women. Also, training can induce inhomogeneous hypertrophy among the quadriceps femoris, thereby leading to different component characteristics of the muscles. If Q-angle is a major determinant of the quadriceps femoris muscularity, it is hypothesized that the sex-related difference in the quadriceps femoris muscularity, if any, is further highlighted in trained individuals, being associated with Q-angle. We tested this hypothesis. Magnetic resonance images of the right thigh were obtained from 26 varsity rowers as trained subjects (13 for each sex) and 34 untrained individuals as controls (17 for each sex). From the images, muscle volume of each constituent of the quadriceps femoris (vastus lateralis, VL; medialis, VM; intermedius; rectus femoris) was determined. The Q-angle was measured during quiet bilateral standing with hand support as needed. Percent volume of VM to the total quadriceps femoris was greater in female rowers than male rowers and female controls, and that of VL was greater in male rowers than male controls. There were no correlations between Q-angle and percent muscle volume in any muscles regardless of rowing experience or sex. The current study revealed that well-trained rowers have sex-related quadriceps femoris muscularity but no significant correlations between percent muscle volume in any muscles and Q-angle. Our findings suggest that Q-angle is not a major determinant of the quadriceps femoris muscularity in either well-trained or untrained individuals.

© 2017 IEEE. Humans utilize their torsos and arms while running to compensate for the angular momentum generated by the lower-body movement during the flight phase. To enable this capability in a humanoid robot, the robot should have human-like mass, a center of mass position, and inertial moment of each link. To mimic this characteristic, we developed an angular momentum control method using a humanoid upper body based on human motion. In this method, the angular momentum generated by the movement of the humanoid lower body is calculated, and the torso and arm motions are calculated to compensate for the angular momentum of the lower body. We additionally developed the humanoid upper-body mechanism that mimics the human link length and mass property by using carbon fiber reinforced plastic and a symmetric structure. As a result, the developed humanoid robot could generate almost the same angular momentum as that of human through human-like running motion. Furthermore, when suspended in midair, the humanoid robot produced the angular momentum compensation in the yaw direction.

The aim of the present study was to measure in vivo skeletal muscle elasticity in the transverse and longitudinal planes using shear wave elastography and then to compare the image stability, measurement values and measurement repeatability between these imaging planes. Thirty-one healthy males participated in this study. Tissue elasticity (shear wave velocity) of the medial gastrocnemius, rectus femoris, biceps brachii and rectus abdominis was measured in both the transverse and longitudinal planes using shear wave elastography. Image stability was evaluated by the standard deviation of the colour distribution in the shear wave elastography image. Measurement repeatability was assessed by the coefficient of variance obtained from three measurement values. Image stability of all tested muscles was significantly higher in the longitudinal plane (P&lt;0.001), but measurement repeatability did not differ significantly between the imaging planes (P&gt;0.05), except in the biceps brachii (P = 0.001). Measurement values of the medial gastrocnemius, rectus femoris and biceps brachii were significantly different between the imaging planes (P&lt;0.001). Image stability and measurement values of shear wave elastography images varied with imaging plane, which indicates that imaging plane should be considered when measuring skeletal muscle tissue elasticity by shear wave elastography.

We investigated localization of damage within the knee extensors (KEs) and plantar flexors (PFs) induced by downhill running (DR) by using transverse relaxation time (T-2)-weighted magnetic resonance imaging (MRI). Fourteen young adults performed 45-min DR (-15% slope) at their maximal tolerable velocity. At pre- and 24, 48, and 72 h post-exercise, T-2-MRI was scanned and T2 values for each muscle composing KEs and PFs at proximal, middle, and distal sites were calculated. Maximal isometric torque and rate of torque development (RTD: 0-30, 0-50, 0-100, 0-200 ms) were also measured. Maximal torque significantly decreased in KEs (14-17%) and PFs (6-8%) at 24-48 h post-exercise, with greater reductions for KEs. RTD in all phases, except for 0-200 ms in PFs, significantly decreased in KEs (11-42%) and PFs (13-23%) at least at one time point post-exercise. T2 significantly increased at several sites (3-5%) in both muscle groups at 24 and/or 48 h post-exercise. Among the T-2-increased sites, the peak effect size (Cohen's d) regarding T-2 change was pronounced at proximal (1.05) and middle (1.64) vastus intermedius compared to the other sites (0.72-0.77). These results suggest that DR induces damage in both KEs and PFs, and especially affects proximal-middle sites of the vastus intermedius.

Many studies have attempted to determine the associations between blood biomarkers and exercise-induced muscle damage. However, poor correlations between the changes in biomarker levels and the magnitude of muscle symptoms have been reported. Recent advances in proteomic tools offer a strategy for the comprehensive analysis of protein expression, which can be used to identify biomarkers. Here, we used a proteomic analysis to identify urinary proteins that appear in response to a calf-raise exercise, including repetitive eccentric muscle contractions, and found that a titin (also known as connectin) N-terminal fragment molecule appears in the urine after eccentric exercise. We measured the titin fragment in urine samples from nine individuals before and after eccentric exercise using a newly-established enzyme-linked immunosorbent assay and found that the titin fragment excretion rate increased 96 h after the exercise (5.1 to 77.6 pg/min, p &lt; 0.01). The changes in the titin fragment excretion rate were correlated strongly with blood markers of muscle damage and with muscle symptoms. These findings suggest that the urinary titin fragment is potentially a noninvasive biomarker of muscle damage.

Purpose
We hypothesized that body mass-to-waist ratio is strongly associated with the total-body skeletal muscle volume (SMV) in children. The purpose of the present study was to examine this hypothesis.
Methods
By using magnetic resonance imaging, total-body SMV (SMVMRI) was determined in 70 boys and 53 girls aged 6 to 12 years. Waist was measured at each of the level of umbilicus (Wumb) and the minimum circumference (Wmin), and the ratio of body mass to each of the two measured values was calculated (BM/Wumb and BM/Wmin, respectively). A single regression analysis was used to examine the relationships between SMVMRI and either BM/Wumb or BM/Wmin. On the basis of the obtained regression equations, SMVMRI was estimated and referred to as SMVBM/Wumb or SMVBM/Wmin.
Results
In both boys and girls, SMVMRI was highly correlated to BM/Wumb (r = 0.937 for boys and r = 0.939 for girls, P &lt; 0.0001) and BM/Wmin (r = 0.915 and 0.942, P &lt; 0.0001). R-2 and the standard error of estimate for SMVBM/Wumb were 0.878 and 706.2 cm(3), respectively, in boys and 0.882 and 825.3 cm(3), respectively, in girls, and those for SMVBM/Wmin were 0.837 and 814.0 cm(3), respectively, in boys and 0.888 and 804.1 cm(3), respectively, in girls. In both boys and girls, there were no significant differences between SMVMRI and either SMVBM/Wumb or SMVBM/Wmin, without systematic errors in Band-Altman plots. There was no significant effect of model on the absolute values of the residuals in both boys and girls.
Conclusion
The current results indicate that body mass-to-waist ratio can be a convenient outcome measure for assessing the total-body skeletal muscle volume in children.

This study examined the validity of segmental bioelectrical impedance (BI) analysis for predicting the fat-free masses (FFMs) of whole-body and body segments in children including overweight individuals. The FFM and impedance (Z) values of arms, trunk, legs, and whole body were determined using a dual-energy X-ray absorptiometry and segmental BI analyses, respectively, in 149 boys and girls aged 6 to 12 years, who were divided into model-development (n = 74), cross-validation (n = 35), and overweight (n = 40) groups. Simple regression analysis was applied to (length)(2)/Z (BI index) for each of the whole-body and 3 segments to develop the prediction equations of the measured FFM of the related body part. In the model-development group, the BI index of each of the 3 segments and whole body was significantly correlated to the measured FFM (R-2 = 0.867-0.932, standard error of estimation = 0.18-1.44 kg (5.9%-8.7%)). There was no significant difference between the measured and predicted FFM values without systematic error. The application of each equation derived in the model-development group to the crossvalidation and overweight groups did not produce significant differences between the measured and predicted FFM values and systematic errors, with an exception that the arm FFM in the overweight group was overestimated. Segmental bioelectrical impedance analysis is useful for predicting the FFM of each of whole-body and body segments in children including overweight individuals, although the application for estimating arm FFM in overweight individuals requires a certain modification.

<p>【目的】下腿後面への器具を用いた軟組織モビライゼーション（IASTM）が足関節柔軟性および筋スティフネスに与える影響を検証した。【方法】健常な成人14名（男性11名・女性３名、24.3±3.5歳）にIASTM条件と安静（CON）条件をそれぞれ別日に実施した。IASTMは下腿後面の軟部組織（腓腹筋内側頭・外側頭、ヒラメ筋、後脛骨筋などの骨格筋、筋膜、アキレス腱などの腱組織の皮膚上からの機械的刺激）を対象に５分間実施した。IASTMとCONの前後で、足関節受動背屈可動域、足関節スティフネス、腓腹筋内側頭およびヒラメ筋の筋腹部分のスティフネス（超音波エラストグラフィ）を測定した。【結果】足関節受動背屈可動域はIASTM後に有意に増加（p＜0.05）、足関節スティフネスはIASTM後に有意に低下した（p＜0.05）。腓腹筋内側頭およびヒラメ筋の筋スティフネスは変化しなかった。CON後ではすべての測定項目が変化しなかった。【結論】IASTMは下腿三頭筋の筋腹以外の軟組織のスティフネス低下を通じて足関節可動性を向上させる。IASTMは足部柔軟性確保のコンディショニング手法として有効である。</p>

The purpose of the present study was to elucidate how plyometric training improves stretchshortening cycle (SSC) exercise performance in terms of muscle strength, tendon stiffness, and muscletendon behavior during SSC exercise. Eleven men were assigned to a training group and ten to a control group. Subjects in the training group performed depth jumps (DJ) using only the ankle joint for 12 weeks. Before and after the period, we observed reaction forces at foot, muscletendon behavior of the gastrocnemius, and electromyographic activities of the triceps surae and tibialis anterior during DJ. Maximal static plantar flexion strength and Achilles tendon stiffness were also determined. In the training group, maximal strength remained unchanged while tendon stiffness increased. The force impulse of DJ increased, with a shorter contact time and larger reaction force over the latter half of braking and initial half of propulsion phases. In the latter half of braking phase, the average electromyographic activity (mEMG) increased in the triceps surae and decreased in tibialis anterior, while fascicle behavior of the gastrocnemius remained unchanged. In the initial half of propulsion, mEMG of triceps surae and shortening velocity of gastrocnemius fascicle decreased, while shortening velocity of the tendon increased. These results suggest that the following mechanisms play an important role in improving SSC exercise performance through plyometric training: (1) optimization of muscletendon behavior of the agonists, associated with alteration in the neuromuscular activity during SSC exercise and increase in tendon stiffness and (2) decrease in the neuromuscular activity of antagonists during a counter movement.

BACKGROUND: This study examined the validity of muscle thickness (MT)-based prediction equation for the muscle volume of the quadriceps femoris (QFMV) by evaluating the applicability of a prediction equation previously derived from young men and by developing a new prediction equation in middle-aged and older individuals. METHODS: The MT at the midpoint of the thigh anterior and QFMV were determined using ultrasonography and magnetic resonance imaging in 30 men and 30 women aged 51 to 77 years. First, we examined the validity of the MT-based prediction equation previously developed for young men to estimate the QFMV of middle-aged and older individuals. Second, we allocated the subjects to validation or cross-validation group and developed a prediction equation for estimating the QFMV using a stepwise multiple regression analysis. RESULTS: The published equation generated a small but a significant difference between the measured and estimated QFMV, with a systematic error depending on the size of QFMV. A multiple regression analysis for the validation group produced the following equation: QFMV (cm3) = (sex × 267.7) + (MT × 249.3) + (thigh length × 41.1) - 1663.7 (sex: man = 1, woman = 0). R 2 and SEE of the regression equation were 0.888 and 124.4 cm3 (12.0 %), respectively. The developed equation was validated and cross-validated. CONCLUSION: For middle-aged and older individuals, the prediction equation previously derived from young men is not applicable, and the newly developed prediction equation with sex, MT, and thigh length as independent variables is applicable for estimating QFMV.

This study examined the influence of regular training in competitive cycling on individual muscle volume of the thigh and psoas major cross-sectionally and longitudinally. T1-weighted magnetic resonance (MR) images of the trunk and right thigh were obtained from eight experienced varsity male cyclists (experience: &gt;4 years) and 10 untrained men (experiment 1), and from 12 (10 males, two females) varsity cyclists before and after competitive cycling training for 6 months (experiment 2). From the MR images, the volumes of each of the quadriceps femoris and hamstrings, total adductors, gracilis, sartorius, and psoas major were determined. The volumes of the monoarticular thigh muscles, semitendinosus, and psoas major muscles were significantly greater in the experienced cyclists than in the untrained men (experiment 1), and increased significantly after the competitive training for 6 months (experiment 2). In contrast, the volumes of the other biarticular thigh muscles were similar among the experienced cyclists and untrained men (experiment 1), and did not change by competitive cycling training (experiment 2). The results indicate that competitive cycling training induces muscle-specific hypertrophy of the synergistic muscles, especially between the monoarticular and biarticular muscles, leading to quantitative profiles of the musculature in experienced cyclists.

Background: Although the sit-to-stand (STS) test score has been shown to relate to the strength and size of the quadriceps femoris (QF) for elderly population, it is unknown whether this relationship is influenced by a posture (i.e., the trunk being allowed to stoop or not) during the STS test. The present study investigated the relationship between STS test score and QF anatomical cross-sectional area (ACSA) in the middle-aged and elderly population with regard to the difference in the posture during STS test, and aimed to develop an accurate predicting equation of the QF ACSA from the STS test score.
Methods: 105 males (40-81 years) and 113 females (41-79 years) participated in the present study, then the subjects were divided at random as validation and cross-validation groups. Mid-thigh QF ACSA was determined by magnetic resonance imaging. Subjects performed a 10-repeated STS as fast as possible in two conditions: (1) with the trunk being allowed to stoop during the sitting phases, and (2) kept upright throughout the test. A power index of the STS test score was calculated based on an equation obtained in a previous study using the time taken for each test condition, the thigh and shank lengths, and body mass. In the validation group (n = 109), a stepwise multiple linear regression analysis was performed to create a predictive model of the ACSA with sex, age, the STS time, and power for both conditions as independent variables. The formulated predictive equation was examined in the cross-validation group (n = 109).
Results: In the validation group, a stepwise regression analysis revealed that STS power with upright trunk condition, sex, and age but not with the stooping condition, were selected as variables to predict QF ACSA (R-2 = 0.64, P &lt; 0.001). There was no systematic error for the relationship between predicted and measured values in the cross-validation group.
Conclusions: These results indicate that STS test score with upright trunk condition is one of the indices of QF muscle size of the middle-aged and elderly population. The estimated predicting equation should be useful in clinical and practical settings for the health promotion.

This study aimed to examine whether muscle activation of the quadriceps femoris differs between single- and multi-joint exercises, and to explore the factors resulting in muscle and exercise specificity in activation.
Eleven adults developed isometric hip extension torque gradually while maintaining submaximal isometric knee extension torque (Experiment 1). In Experiment 2, 15 men performed knee extension and leg press separately at intensities of 20, 40, 60 and 80 % of their one repetition maximum (1RM) load, and 14 men conducted leg press at intensities of 40 and 80 % of 1RM until exhaustion (Experiment 3). Muscle activation during exercises was measured using surface electromyography from the rectus femoris, vastus lateralis and medialis.
The addition of isometric hip extension torque significantly decreased rectus femoris activation (Experiment 1). In Experiment 2, the rectus femoris activation was significantly higher during knee extension than during leg press, whereas no differences were observed in the vasti. The rectus femoris activation was not significantly different between leg press at 80 % and knee extension at 20 % of 1RM. The results of Experiment 3 showed significant increases in vasti activation at both intensities, whereas rectus femoris activation did not change at 80 % of 1RM.
The results revealed that even at high intensity, the rectus femoris activation during multi-joint exercise is low and does not increase with fatigue, unlike the vasti, and that the inter-muscle and inter-exercise differences in activation depend on whether hip extension torque is exerted in the exercise.

Human steady running is modeled using a spring-loaded inverted pendulum (SLIP). However, human pushes off the ground actively when starting to run. In this study, we describe a knee joint mechanism for coping with both of an active pushing-off and joint stiffness needed to continue running. To achieve this, knee is equipped with a mechanism comprising a worm gear that improves torque transmission efficiency in order to achieve active movement and two laminated leaf springs for mimicking joint stiffness. We evaluated the performance of the laminated leaf spring and performed an experiment in which the developed running robot started to run. Using the proposed mechanisms, this robot could accomplish hopping with an active pushing-off motion and continued to run using its joint elasticity.

Purpose: To assess the effect of exercise-induced muscle damage on muscle hardness and evaluate the relationship between muscle hardness and muscle damage indicators.
Methods: Seven men (mean 25.3 years; 172.7 cm; 66.8 kg) performed the single-leg ankle plantar flexion exercise involving both concentric and eccentric contractions (10 sets of 40 repetitions). The hardness of the medial gastrocnemius (MG) was evaluated using ultrasound real-time tissue elastography before, from day 1 to 4, and day 7 after exercise. The strain ratio between the MG and a reference material was calculated. Simultaneously, we evaluated the magnetic resonance T2 value (an index of edema) of the triceps surae, the ankle dorsiflexion range of motion (ROM), and calf muscle soreness. Serum creatine kinase activity was assessed before, 2 and 4 h, and from day 1 to 4 after exercise.
Results: The MG showed lower strain ratio, indicating increased muscle hardness, on day 4 post-exercise (P &lt; 0.01) and higher T2 values on days 1-7 post-exercise (P &lt; 0.01) relative to each pre-exercise value. The ankle dorsiflexion ROM was lower on days 2-4 post-exercise (P &lt; 0.01). The serum creatine kinase markedly increased on days 3 and 4 post-exercise (not significant). The degree of muscle soreness among the post-exercise time points was similar. The decreased strain ratio did not correlate with the increased T2, the decreased joint ROM or muscle soreness.
Conclusion: Muscle hardness increased after strenuous resistance exercise, but the change was not related with muscle edema, decreased joint ROM, or muscle soreness resulting from muscle damage.

The aims of this study were to determine contraction-induced changes in the elbow flexor cross-sectional area (CSA) and to examine whether the maximal CSA during a high-intensity contraction is more closely related to the strength than that at rest in the elbow flexors. Fourteen young male subjects participated in this study. The elbow flexor CSAs were measured at sites from 1 cm proximal to 6 cm distal to the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) (every 1 cm; 8 sampling sites) using magnetic resonance imaging, at rest and during 10, 20, 40, 60, and 80% of maximal voluntary contraction (MVC) of isometric elbow flexion. The elbow flexor CSA changed greatly during low-intensity contractions, and this contraction-induced change was small over 60% MVC. Compared with at rest, greater CSA around the muscle belly and smaller CSA in the distal portion of the elbow flexors were found in contracted conditions. The MVC strength was significantly correlated with the maximal CSAs at rest and each contraction level, but stepwise multiple regression analysis selected only that during 80% MVC as a significant contributor for estimating the MVC strength. These results suggest that, in the elbow flexors, the contraction-induced change in the CSA reaches its peak under high contractile level and that the maximal CSA during 80% MVC is more closely related to the MVC strength than that at rest.

Although the moment arm of the triceps brachii muscle has been shown to be associated with the muscle's anatomical cross-sectional area, whether training-induced muscle hypertrophy alters the moment arm of the muscle remains unexplored. Therefore, the current study aimed to examine this. Eleven men underwent a 12-week resistance training program for the triceps brachii muscle. The maximum muscle anatomical cross-sectional area (ACSA(max)), the moment arm of the triceps brachii muscle, and the anterior-posterior dimension of the olecranon were measured using a magnetic resonance imaging system before and after intervention. The ACSA(max) (33.6 +/- 11.9%, P &lt; .001) and moment arm (5.5 +/- 4.0%, P = .001) significantly increased after training, whereas the anterior-posterior dimension of the olecranon did not change (P&gt;.05). The change in moment arm was smaller than that expected from the relationship between the ACSAmax and the moment arm before the intervention. The present results indicate that training-induced triceps brachii muscle hypertrophy could increase the muscle moment arm, but its impact can be small or negligible.

Most sporting compression stockings possess a graduated pressure profile. However, it remains unclear whether the graduated pressure profile is an essential feature for reducing the development of muscle fatigue. This study sought to examine the effect of the pressure profile of compression stockings on the degree of muscle fatigue of lower leg muscles induced by submaximal running exercise. 15 male subjects performed 30-min treadmill running in 1 control and 4 compression stocking conditions with the following profiles; 1) graduated low pressure, 2) graduated high pressure, 3) uniform pressure distribution, and 4) localized pressure just over the gastrocnemius muscle belly. Before and immediately after the exercise, T2-weighted magnetic resonance images of the right lower leg were obtained without testing garments. T2 values of the triceps surae and tibialis anterior were calculated from the images. T2 was significantly increased after the running in all conditions. The magnitude of T2 increase was significantly greater in the control than in other 3 conditions except for the one with graduated low pressure, whereas there were no significant differences among the latter 3 conditions. The findings suggest that a graduated pressure profile is not an essential feature of compression stockings for reducing the development of muscle fatigue during submaximal running exercise.

Inability to control lower extremity segments in the frontal and transverse planes resulting in large knee abduction angle and increased internal knee abduction impulse has been associated with patellofemoral pain (PFP). However, the influence of hip rotation angles on frontal plane knee joint kinematics and kinetics remains unclear. The purpose of this study was to explore how hip rotation angles are related to frontal plane knee joint kinematics and kinetics during running. Seventy runners participated in this study. Three-dimensional marker positions and ground reaction forces were recorded with an 8-camera motion analysis system and a force plate while subjects ran along a 25-m runway at a speed of 4 m/s. Knee abduction, hip rotation and toe-out angles, frontal plane lever arm at the knee, internal knee abduction moment and impulse, ground reaction forces and the medio-lateral distance from the ankle joint center to the center of pressure (AJC-CoP) were quantified. The findings of this study indicate that greater hip external rotation angles were associated with greater toe-out angles, longer AJC-CoP distances, smaller internal knee abduction impulses with shorter frontal plane lever arms and greater knee abduction angles. Thus, there appears to exist a conflict between kinematic and kinetic risk factors of PFP, and hip external rotation angle may be a key factor to control frontal plane knee joint kinematics and kinetics. These results may help provide an appropriate manipulation and/or intervention on running style to reduce the risk of PFP. (C) 2014 Elsevier B.V. All rights reserved.

This brief review summarizes available evidence on the quantitative profiles of the quadriceps femoris in sports athletes. It is generally believed that sports athletes show event-related morphological profiles in muscle size that are specific to their competitive and training activities. Many previous analyses of cross-sectional data have indicated that athletes have greater size of the quadriceps femoris as comparedto untrained controls. However, little is known about which events have athletes with the greatest degree of quadriceps femoris. In addition, longitudinal studies on the adaptation of the quadriceps are few, and there is a paucity of quantitative evidence onadaptations of the quadriceps femoris induced by regular training for competitive activities. Only a limited number of studies have been carried out to examine the association between quadriceps femoris size and sport performance, e.g., sprinters, weightlifters and cyclists, with the conclusions controversial and inconsistent across studies. Furthermore, little is known regarding inter-muscle and/or intra-muscle differences inthe hypertrophic response, either in cross-sectional or longitudinal studies. There ishowever strong evidence that resistance training-induced changes in muscle size do notoccur evenly among the four muscles of the quadriceps femoris, nor along or across thesame muscle. Further studies will be needed if we are to develop an understanding of the mechanisms leading to the many differences seen in the quadriceps femoris, both within and across athletes.

Analysis of human running has revealed that the motion of the human leg can be modeled by a compression spring because the leg's joints behave like a torsion spring in the stance phase. Moreover, the knee bends rapidly to avoid contact of the foot with the ground in the swing phase. In this paper, we describe the development of a knee joint mechanism that mimics the elastic characteristics of the stance leg and rapid bending knee of the idling leg of a running human. The knee was equipped with a mechanism comprising two leaf springs and a worm gear for adjusting the joint stiffness and high-speed bending knee. Using this mechanism, we were able to achieve joint stiffness within the range of human knee joints that could be adjusted by varying the effective length of one of the leaf springs. In addition, the mechanism was able to bend rapidly by changing the angle between the two leaf springs. The equation proposed for calculating the joint stiffness considers the difference between the position of the fixed point of the leaf spring and the position of the rotational center of the joint. We evaluated the performance of the adjustable joint stiffness and the effectiveness of the proposed equation for joint stiffness and high-speed knee bending. We were able to make a bipedal robot hop using pelvic oscillation for storing energy produced by the resonance to leg elasticity and confirmed the mechanism could produce large torque 210 Nm.

Human running motion can be modeled using a spring-loaded inverted pendulum (SLIP), where the linear-spring-like motion of the standing leg is produced by the joint stiffness of the knee and ankle. To use running speed control in the SLIP model, we should only decide the landing placement of the leg. However, for using running speed control with a multi-joint leg, we should also decide the joint angle and joint stiffness of the standing leg because these affect the direction of the ground reaction force. In this study, we develop a running control method for a human-like multi-joint leg. To achieve a running motion, we developed a running control method including pelvis oscillation control for attaining jumping power with the joint stiffness of the leg and running speed control by changing the landing placement of the leg. For using running speed control, we estimated the ground reaction force using the equation of motion and detected the joint angles of the leg for directing the ground reaction force toward the center of mass. To evaluate the proposed control methods, we compared the estimated ground reaction force with the force measured by the real robot. Moreover, we performed a running experiment with the developed running robot. By using ground reaction force estimation, this robot could accomplish the running motion with pelvic oscillation for attaining jumping power and running speed control.

Purpose: Existing studies have failed to provide evidence of a positive effect on exercise performance by wearing compression short tights covering only both thighs. This could be due to an inadequate pressure intensity that otherwise has a significant effect if applied on the crucial point in the thigh. This study aimed to examine the effect of pressure intensity of elastic compression short-tights on the metabolic state of thigh muscles during submaximal running. Methods: Two groups of 11 male subjects performed treadmill running at 12 km.h(-1) in three conditions in each of experiment 1 (short-tights with a compression intensity at the thigh of 8 mm Hg (LOW) and 15 mm Hg (MID) and noncompression shorts as control (CON1)) and experiment 2 (short-tights with 20 mm Hg (MID-HIGH) and 25 mm Hg (HIGH) and CON2). Before and immediately after the running exercises, T2-weighted magnetic resonance images of the right thigh were obtained without testing garments. From the images, skeletal muscle proton transverse relaxation time (T2) of each muscle in the thigh was calculated. Results: T2 was significantly increased after the treadmill running in all conditions in the hamstring and adductor muscles. In experiment 1, after the running, T2 elevation was significantly smaller in MID than that in CON1 for the biceps femoris, semimembranosus, adductor longus, and adductor magnus muscles. In experiment 2, after the running, T2 elevation was significantly lower in MID-HIGH than that in CON2 and HIGH for the biceps femoris, semimembranosus, and adductor longus. Conclusions: The findings suggest that wearing compression short tights with a pressure intensity of 15-20 mm Hg at the thigh can reduce development of fatigue of exercising muscles during submaximal running exercise in healthy adult males.

The present study aimed to re-examine the influence of the isometric plantarflexors contraction on the Achilles tendon moment arm (ATMA) and the factors influencing the ATMA in three-dimensions. A series of coronal magnetic resonance images of the right ankle were recorded at foot positions of 10 degrees of dorsiflexion, neutral position, and 10 degrees of plantarflexion for the rest condition and the plantarflexors contraction condition at 30% maximal voluntary effort The shortest distance between the talocrural joint axis and the line of action of the Achilles tendon force projected to the orthogonal plane of the talocrural joint axis was determined as the ATMA. The ATMA determined in the contraction condition was significantly greater by 8 mm than that determined in the rest condition. The talocrural joint axis was displaced anteriorly by 3 mm and distally by 2 mm due to the muscle contraction. As the same time, the line of action of the Achilles tendon force was displaced posteriorly by 5 mm and medially by 2 mm. These linear displacements of the talocrural joint axis and the line of action of the Achilles tendon force accounted for the difference in the ATMAs between the two conditions by 35.9 and 62.4%, respectively. These angular displacements accounted for the total of 0.4% increase in the ATMA. These results confirm the previous findings reported in two-dimensional studies and found that the linear displacement of the line of action of the Achilles tendon force is the primary source of the contraction-induced increase in the ATIVIA. (C) 2014 Elsevier Ltd. All rights reserved.

Jump performance can be enhanced after performing squat exercises, and this is thought to be because of the phenomenon of postactivation potentiation (PAP). However, the influence of the intensity of squat exercises on jump performance enhancement and its association to PAP have not been elucidated. Thus, we examined the influence of the intensity of squat exercises on the subsequent jump performance and the magnitude of PAP. Eight weightlifters (age, 19.8 +/- 1.3 years; height, 1.67 +/- 0.07 m; body mass, 77.1 +/- 14.8 kg) were recruited as subjects. The intensity of squat exercises was set in 2 conditions: heavy condition (HC) (45% 1 repetition maximum [1RM] x 5 repetitions [reps], 60% 1RM x 5 reps, 75% 1RM x 3 reps, and 90% 1RM x 3 reps) and moderate condition (MC) (45% 1RM x 5 reps, 60% 1RM x 5 reps, and 75% 1RM x 3 reps). Before and after the squat exercises, the subjects performed countermovement jumps 3 times. In addition, a twitch contraction was concurrently elicited before and after the squat exercises. In both conditions, twitch torque and jump height recorded after the squat exercises increased significantly compared with those recorded beforehand. The extents of increase in both twitch torque and jump height were significantly larger in HC than in MC. We conclude therefore that a high-intensity squat exercise is better than a moderate-intensity squat exercise as a warm-up modality for enhancing subsequent jump performance.

Objective: This study aimed to examine the applicability of ultrasound muscle thickness (MT) measurements for predicting whole body fat-free mass (FFM) in elderly individuals. Design and setting: Crosssectional study of 77 healthy elderly individuals. Methods: MTs at nine sites of the body and FFM were determined using B-mode ultrasound and dual-energy x-ray absorptiometry (DXA), respectively, in 44 women and 33 men aged 52 to 78 yrs. Stepwise multiple regression analysis produced two equations for predicting DXA-based FFM with sex (dummy: woman = 0 and man = 1) and either MTs at the anterior and posterior of thigh and lower leg (Eq1) or the product of MT and limb length (MTxLL) at thigh anterior and posterior, lower leg posterior, and upper arm anterior (Eq2) as independent variables. Results: The R2 and SEE for each of the two equations were 0.929 and 2.5 kg for Eq1 and 0.955 and 2.0 kg for Eq2. The estimated FFM from each of Eq1 (44.4 +/- 8.9 kg) and Eq2 (44.4 +/- 9.0 kg) did not significantly differ from that of the DXA-based FFM (44.4 +/- 9.2 kg), without systematic error. However, the absolute value of the difference between the DXA-based and estimated FFM was significantly greater with Eq1 (2.0 +/- 1.5 kg) than with Eq2 (1.5 +/- 1.3 kg). Conclusion: The current results indicate that ultrasound MT measurement is useful to predict FFM in the elderly, and its accuracy is improved by using the product of MT and limb length as an independent variable.

The purpose of this study was to examine the morphological profiles of 4 constituents (vastus lateralis, vastus medialis, vastus intermedius and rectus femoris) of the quadriceps femoris in oarsmen through comparison with non-athletes. T1-weigheted magnetic resonance (MR) images of the thigh were obtained from 14 oarsmen and 19 non-athlete men. From the MR images, serial anatomical cross-sectional areas (ACSAs) and muscle volume of each muscle were determined. The muscle volume of the total quadriceps femoris, vastus lateralis, vastus medialis and vastus intermedius were significantly larger in the oarsmen than in the non-athlete men, whereas that of the rectus femoris was comparable for the 2 groups. The portion of the rectus femoris as a percentage of total quadriceps femoris volume was significantly higher in the non-athlete men than in the oarsmen, and vice versa for the vastus lateralis. The proximal-to-distal and middle-to-distal ACSA ratios in each muscle did not differ between the 2 groups. The present results indicate inferior muscular hypertrophy of the rectus femoris compared to the vasti in oarsmen, and that the vasti are equally hypertrophied along their lengths. This may be due to muscle-specific adaptation to the rowing exercise.

We aimed to examine whether the influence of conditioning contraction intensity on the extent of post-activation potentiation (PAP) is muscle dependent. Eleven healthy males performed both thumb adduction and plantar flexion as a conditioning contraction. The conditioning contraction intensities were set at 20%, 40%, 60%, 80%, or 100% of the maximal voluntary isometric contraction (MVC).
Before and after the conditioning contraction, twitch torque was measured for the respective joint to calculate the extent of PAP. In plantar flexion, the extent of PAP became significantly larger as the conditioning contraction intensity increased up to 80% MVC (p &lt; 0.05). In contrast, the extent of PAP in thumb adduction increased significantly only up to 60% MVC (p &lt; 0.05), but not at higher intensities.
These results indicate that the influence of the conditioning contraction intensity on the extent of PAP is muscle dependent. Our results suggest that a conditioning contraction with submaximal intensity can sufficiently evoke sizable PAP in the muscle where most of muscle fibers are recruited at submaximal intensities, thereby attenuating muscle fatigue induced by the conditioning contraction. (C) 2014 Elsevier Ltd. All rights reserved.

The knee is the most common site of running injuries, particularly prevalent in females. The purpose of this study was to clarify gender differences in the lower extremity kinematics during running, with a specific emphasis on the relationships between the distal and proximal factors and the knee joint kinematics. Eleven female and 11 male runners participated in this study. Three-dimensional marker positions were recorded with a motion analysis system while the subjects ran along a 25 m runway at a speed of 3.5 m/s. Kinematic variables were analyzed for the stance phase of the right leg. Female runners demonstrated significantly greater peak knee abduction (P&lt;0.05), hip adduction (P&lt;0.01) and internal rotation (P&lt;0.05), whereas male runners demonstrated significantly greater peak rearfoot eversion (P&lt;0.01). The knee abduction angles were positively correlated with hip adduction angles (r=0.49, P&lt;0.05) and negatively correlated with rearfoot eversion (r= -0.69, P&lt;0.001). There was no significant difference in normalised step width between genders (P&gt;0.05). Smaller rearfoot eversion and greater hip adduction related closely to the greater knee abduction as the distal and proximal factors, respectively. These relationships are thought to be the compensatory joint motions in the frontal plane, because there was no significant difference in the normalised step width between females and males. The current results suggest that if the step width is identical, the subjects with greater knee abduction had smaller rearfoot eversion to compensate for greater hip adduction, which were more apparent in females. This explains greater knee abduction found in female runners, which can be linked to a high risk of knee injury.

This investigation determined whether existing muscle damage markers and organ damage markers respond to an acute eccentric exercise protocol and are associated with affected muscle symptoms. Nine healthy-young men completed one-leg calf-raise exercise with their right leg on a force plate. They performed 10 sets of 40 repetitions of exercise at 0.5 Hz with a load corresponding to half of their body weight, with 3 mm rest between sets. The tenderness of medial gastrocnemius, lateral gastrocnemius and soleus, and the ankle active range of motion (ROM) were assessed before, immediately after, 24 h and 48 h, 72 h, 96 h and 168 h after exercise. Blood and urine were collected pre-exercise and 2 h, 4 h, 24 h, 48 h, 72 h and 96 h post-exercise. Serum was analyzed for creatine kinase (CK), aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and aldolase (ALD) activities. We also determined hearttype fatty acid-binding protein (H-FABP), intestinal-type fatty acid-binding protein (I-FABP) and liver-type fatty acid-binding protein (L-FABP), neutrophil gelatinase-associated lipocalin (NGAL), interleukin (IL)-17A, IL-23, nerve growth factor (NGF), soluble-Endothelial (sE)-selectin, s-Leukocyte (L)-selectin, 5Platelets (P)-selectin, and 8-isoprostane in plasma and urine. The tenderness of proximal and middle gastrocnemius increased significantly 72 h (p&lt;0.05, p&lt;0.01) after exercise. Ankle active ROM in dorsal flexion decreased significantly 48 h (p&lt; 0.05) and 72 h (p&lt;0.01) after exercise. CK and ALD activities significantly increased at 72 h (p&lt;0.05) and remained elevated at 96 h (p&lt; 0.01) postexercise compared to pre-exercise values. Also, ALD which showed relatively lower interindividual variability was significantly correlated with tenderness of middle gastrocnemius at 72 h. LDH activity significantly increased 96 h postexercise (p&lt; 0.01), whereas the increase in AST and ALT activities 96 h post-exercise was not significantly different from pre-exercise values. There were no significant changes in FABPs, NGAL, IL-17A, IL-23, NGF, selectins and 8-isoprostanes in plasma and urine. In conclusion, calf-raise exercise induced severe local muscle damage symptoms which were accompanied by increases in both serum CK and ALD activities, but we could not detect any changes in examined markers of organ damage, inflammation and oxidative stress. Further research is needed to determine other more sensitive biomarkers and the underlying mechanisms of exercise-induced muscle damage.

Purpose: This study aimed to ascertain whether training-induced muscle hypertrophy is accompanied by an increase in the aponeurosis width, and to infer its impact on the training-induced increase in the pennation angle.
Methods: Eleven young men completed a resistance training program of unilateral knee extensions for 12 weeks. Before and after training, anatomical cross-sectional area (ACSA) of the vastus lateralis and its distal aponeurosis width in the transverse plane were measured with magnetic resonance imaging. The pennation angle and fascicle length were also determined with ultrasonography at the midbelly of the muscle. The effect of change in aponeurosis width on the magnitude of training-induced increase in pennation angle was estimated by using a parallelepipedon model.
Results: After the training, there were significant increases in ACSA (10.7 ± 7.6 %), pennation angle (10.8 ± 7.3 %) and aponeurosis width (1.9 ± 3.1 %), whereas no significant change was found in the fascicle length. The model simulation shows that the increase in aponeurosis width by 1.9 % reduces the magnitude of increase in pennation angle by only 0.4°.
Conclusions: These results indicate that (1) the aponeurosis width of the vastus lateralis increases after 12 weeks of resistance training and (2) the increase in the aponeurosis width accompanying muscle hypertrophy by the amount of ~10 % does not substantially affect the increase in pennation angle.

Human running motion can be modeled by a spring loaded inverted pendulum (SLIP). However, this model, despite being widely used in robotics, does not include human-like pelvic motion. In this study, we show that the pelvis actually contributes to the increase in jumping force and absorption of landing impact, both of which findings can be used to improve running robots. On the basis of the analysis of human running motion, we propose a new model named SLIP 2 (spring loaded inverted pendulum using pelvis). This model is composed of a body mass, a pelvis, and leg springs; the model can control its springs during running by use of pelvic movement in the frontal plane. To achieve hopping and running motions, we developed pelvis oscillation control, running velocity control, and stabilization control using an upper body, as control methods. We also developed a new hopping robot using the SLIP 2 model. To evaluate the proposed model and control methods, we performed hopping and running simulations. The simulation results showed that the SLIP 2 model successfully achieves hopping and running motions. The hopping robot was also able to accomplish hopping motion. The simulation results also showed that the difference between the pelvic rotational phase and the phase of oscillation of the mass vertical displacement affects the jumping force. In particular, the results revealed that the human-like pelvic rotation contributes to the absorption of landing impact and to the increase in takeoff forces, which validates our observations in human motion analysis.

Analysis of human running has revealed that the motion of the human leg can be modeled by a compression spring because leg’s joints behave like a torsion spring. In addition, the pelvic movement in the frontal plane contributes to the increase in jumping force. We therefore assumed that human-like running, which requires higher output power than that of existing humanoid robots, could be realized based on these characteristics. Hence, we developed a model composed of a body mass, a pelvis and a rotational joint leg, and fabricated the leg by incorporating a stiffness adjustment mechanism that uses two leaf springs. In this way, we were able to achieve a human-like joint stiffness, which could be adjusted by varying the effective length of one of the leaf springs. We achieved hopping by resonance of the pelvic movement and joints’ elasticity.

In this paper, we describe the development of a leg with a rotational joint that mimics the elastic characteristics of the leg of a running human. The purpose of this development was to realize the dynamics of human running, the analysis of which has revealed that the motion of the leg can be modeled by a compression spring and that of the leg joint by a torsion spring. We, therefore, assumed that these elastic characteristics could be used to develop robots capable of human-like running, which requires higher output power than that of existing humanoid robots. Hence, we developed a model of a leg with a rotational joint and fabricated the leg by incorporating a mechanism comprising of two leaf springs for adjusting the joint stiffness. By this means, we were able to achieve human-like joint stiffness, which could be adjusted by varying the effective length of one of the leaf springs. We evaluated the performance of the adjustable stiffness of the joints, and were also able to achieve hopping by resonance of the rotational leg joint.

健康な成人男性8名(身長1.69±0.04m、体重62.8±6.5kg、25±2歳)を対象に、ヒト生体腱におけるつま先領域と線形領域を正確にモデル化し、境界点における腱伸張および腱張力の値を推定する方法を提案した。maximal voluntary contraction(MVC)は日間で有意差が認められず、変動係数(CV)は3.1±1.5%であった。境界点における腱伸張は日間で有意差が認められず、CVは3.9±3.2%であった。境界点における腱張力は日間で有意差が認められず、CVは7.7±3.7%であった。ΔX nの算出区間を変えた場合の境界点における腱伸張および腱張力の値はそれぞれ10.1±2.1mm(1日目)、10.2±2.2mm(2日目)、1348.7±437.5Nm(1日目)、1300.0±483.4Nm(2日目)であった。いずれの値も10%MVCごとに算出した場合と有意な差は認めなかった。

Purpose: Muscle hypertrophy in response to resistance training has been reported to occur nonuniformly along the length of the muscle. The purpose of the present study was to examine whether the regional difference in muscle hypertrophy induced by a training intervention corresponds to the regional difference in muscle activation in the training session. Methods: Twelve young men participated in a training intervention program for the elbow extensors with a multijoint resistance exercise for 12 wk (3 d.wk(-1)). Before and after the intervention, cross-sectional areas of the triceps brachii along its length were measured with magnetic resonance images. A series of transverse relaxation time (T2)-weighted magnetic resonance images was recorded before and immediately after the first session of training intervention. The T2 was calculated for each pixel within the triceps brachii. In the images recorded after the session, the number of pixels with a T2 greater than the threshold (mean + 1 SD of T2 before the session) was expressed as the ratio to the whole number of pixels within the muscle and used as an index of muscle activation (percent activated area). Results: The percent activated area of the triceps brachii in the first session was significantly higher in the middle regions than that in the most proximal region. Similarly, the relative change in cross-sectional area induced by the training intervention was also significantly greater in the middle regions than the most proximal region. Conclusion: The results suggest that nonuniform muscle hypertrophy after training intervention is due to the region-specific muscle activation during the training session.

Purpose: This study aimed to clarify whether resistance training-induced changes in muscle architecture are homogeneous among the quadriceps and over different regions within each muscle. Methods: Eleven recreationally active men (27 ± 2 years) completed a 12-week resistance training program for knee extensors. Before and after the intervention, muscle thicknesses, fascicle lengths, and pennation angles of the four muscles (vastus lateralis, vastus medialis, vastus intermedius, rectus femoris) in several regions (2-4 regions per each muscle) were measured using ultrasonography. Anatomical cross-sectional areas (ACSAs) at the same positions as the ultrasound measurements were determined from magnetic resonance images. Results: Relative increases in the ACSA, muscle thickness, and pennation angle of the rectus femoris were significantly greater than those of the vasti. Relative increases in the ACSAs of the vastus lateralis and rectus femoris were significantly greater in the distal than in the proximal region, and those in the muscle thickness and pennation angle of the vastus intermedius were significantly greater in the medial than in the lateral region. Fascicle lengths did not change in any muscles. The interrelations between muscle thickness and pennation angle remained unchanged after the intervention, with a significant association between the relative changes of the two variables. Conclusion: The current results indicate that (1) hypertrophy of the quadriceps femoris is associated with a proportional increase in pennation angle but not necessarily in fascicle length, and (2) training-induced changes in muscle size and pennation do not evenly occur among the quadriceps, along or across a muscle. © 2013 Springer-Verlag Berlin Heidelberg.

BACKGROUND: The skeletal muscle mass of the lower limb plays a role in its mobility during daily life. From the perspective of physical resources, leg muscle mass dominantly decreases after the end of the fifth decade. Therefore, an accurate estimate of the muscle mass is important for the middle-aged and older population. The present study aimed to clarify the validity of ultrasound muscle thickness (MT) measurements for predicting leg skeletal muscle mass (SM) in the healthy Japanese middle-aged and older population. FINDINGS: MTs at four sites of the lower limb and the bone-free lean tissue mass (LTM) of the right leg were determined using brightness-mode ultrasonography and dual-energy X-ray absorptiometry (DXA), respectively, in 44 women and 33 men, 52- to 78-years old. LTM was used as a representative variable of leg skeletal muscle mass. In the model-development group (30 women and 22 men), regression analysis produced an equation with R2 and standard error of the estimate (SEE) of 0.958 and 0.3 kg, respectively: LTM (kg) = 0.01464 × (MTSUM×L) (cm2) - 2.767, where MTSUM is the sum of the product of MTs at four sites, and L is length of segment where MT is determined. The estimated LTM (7.0 ± 1.7 kg) did not significantly differ from the measured LTM (7.0 ± 1.7 kg), without a significant systematic error on a Bland-Altman plot. The application of this equation for the cross-validation group (14 women and 11 men) did not yield a significant difference between the measured (7.2 ± 1.6 kg) or estimated (7.2 ± 1.6 kg) LTM and systematic error. CONCLUSION: The developed prediction equation may be useful for estimating the lean tissue mass of the lower extremity for the healthy Japanese middle-aged and older population.

The purpose of this study was to examine the relationship between muscle architecture of the triceps brachii (TB) and joint performance during concentric elbow extensions. Twenty-two men performed maximal isometric and concentric elbow extensions against various loads. Joint torque and angular velocity during concentric contractions were measured, and joint power was calculated. Muscle length, cross-sectional areas, and volume of TB were measured from magnetic resonance images. Pennation angle (PA) of TB at rest was determined by ultrasonography. The PA was significantly correlated with the maximal isometric torque (r = .471), but not to the torque normalized by muscle volume (r = .312). A significant correlation was found between PA and the angular velocity at 0 kg load (r = .563), even when the angular velocity was normalized by the muscle length (r = .536). The PA was significantly correlated with the maximal joint power (r = .519), but not with the power normalized by muscle volume (r = .393). These results suggest that PA has a positive influence on the muscle shortening velocity during an unloaded movement, but does not have a significant influence on the maximum power generation in untrained men.

The architectural feature of the rectus femoris (RF) has been scarcely investigated despite its substantial contribution to knee extension torque and large plasticity in the muscularity. This study aimed to examine the reproducibility and validity of ultrasound measurements of RF architecture and interrelationships among the architectural parameters. After confirming the measurement accuracy of an examiner (measurement errors &lt;1%), in vivo and cadaveric measurements of fascicle lengths and pennation angles of RF were performed. Day-to-day reproducibility of measurements was investigated in vivo including muscle thickness measurement. Validity of measurements was investigated by comparing the values between direct and ultrasound measurements for the cadaver. The intraclass correlation coefficients were 0 center dot 984, 0 center dot 960 and 0 center dot 932, and root mean square difference between measured values on 2days was 0 center dot 8mm, 3 center dot 1mm and 1 center dot 4 degrees for muscle thickness, fascicle length and pennation angle, respectively. The validity of measurements was similar or better than those of previous reports on other muscles. We also confirmed a positive correlation between the muscle thickness and the pennation angle as has been shown in other muscles. The current results warrant the use of B-mode ultrasonography for examining the architectural characteristics of RF in vivo.

Purpose: One bout of 5-6 s of maximal voluntary isometric contraction (MVC) is known to enhance subsequent dynamic joint performance such as dynamic joint torque and power with maximal voluntary effort. On the other hand, such a muscle contraction can also induce muscle fatigue. It is then possible that individual differences in fatigue resistance is a factor that affects the balance between potentiation and fatigue. Here, we examined the effect of chronic heavy-resistance training on the extent and time course of the potentiation of maximal voluntary dynamic torque. Methods: Before and after a 12-wk intervention, maximal voluntary concentric knee extension torque at 210 degrees.s(-1) was measured in the following sequence: before and immediately after a 5-s MVC of knee extension and 1, 3, and 5 min thereafter. The training group performed heavy-resistance training exercise of knee extension consisting of five sets of eight repetitions with 80% of one-repetition maximum, three sessions a week during the intervention period. Results: Before the resistance training intervention, maximal voluntary concentric torque was significantly enhanced only at 1 and 3 min post-MVC. After the 12-wk resistance training, the maximal voluntary concentric torque was potentiated also immediately after the conditioning MVC and was further increased at 1-min point. Conclusion: These findings indicate that the contraction-induced potentiation of maximal voluntary dynamic torque is pronounced in strength-trained individuals.

We have developed a flapping robot with active feathering wings by using a "scissors swing motor (SSM)". In the present study, we investigate how the feathering motion, which changes the angle of attack of the wing, affects the lift by means of motion capture experiment. Infrared reflective makers were placed on the wing frames, and their 3D-coordinates were tracked. The weight change of the robot was monitored simultaneously with a load cell, and we measured the lift force produced by flapping motion. The results show that deformation of wing surface during the flapping motion deteriorates the lift, and the feathering motion effectively suppresses the deformation of the wing.

To better understand the cascade from neural activation up to force production within in vivo contracting muscle-tendon units, we estimated activation of contractile elements from experimentally measured human fascicle length change and force using a Hill-type muscle model. The experiment was conducted with respect to twitch contractions of the tibialis anterior muscle at three joint angles. As muscle contractile element force is a function of its length and velocity, the activation of contractile elements was calculated using a Hill-type muscle model and measured data. The results were able to reproduce the continuous rising activation of contractile elements after termination of electromyographic activity, the earlier shift of peak activation in time compared to twitch force, and the differences in time-course activation at three different joint angles. These findings are consistent with the predicted change in the activation of contractile elements from previous reports. Also, the results suggest that the time-course of the activation of contractile elements was greatly influenced by the change in force generating capacities related to both length and velocity, even in fixed end contractions, which could result from muscle-tendon interaction. © 2013 Taylor &amp
Francis.

Not only twitch torque but also the maximal voluntary concentric torque increases after a high-intensity contraction (conditioning contraction). The purpose of this study was to test the hypothesis that the increase in the maximal voluntary concentric torque induced by a conditioning contraction is prominent when tested at fast angular velocities conditions. Twelve healthy male participants performed the maximal voluntary isometric plantar flexion for six seconds as a conditioning contraction. Before and after the conditioning contraction, peak torques during the maximal voluntary concentric plantar flexions were measured at 30°/s (slow) and 180°/s (fast), each of which was carried out in a separate condition. Isometric twitch torque was also recorded before and after the conditioning contraction in each of the two velocity conditions to confirm the extent of the positive effect of the conditioning contraction. The extent of increase in isometric twitch torque was similar between the two velocity conditions, whereas the maximal voluntary concentric torque increased significantly only in the fast velocity condition (p = 0.003). These results support the hypothesis and indicate that the maximal voluntary concentric torque can be potentiated by the conditioning contraction if the joint angular velocity during the maximal voluntary concentric contraction is sufficiently high. © 2013 Fukutani et al.

MIYAMOTO, N., H. KANEHISA, and Y. KAWAKAMI. Potentiation of Maximal Voluntary Concentric Torque in Human Quadriceps Femoris. Med. Sci. Sports Exerc., Vol. 44, No. 9, pp. 1738-1746, 2012. Purpose: Previous studies have shown that one bout of 6-s maximal voluntary contraction (MVC) can enhance subsequent dynamic joint performance with maximal voluntary effort. However, the conditioning contraction also induces central fatigue, which attenuates the enhancement of the subsequent voluntary joint performance. Here, as a modality for minimizing the fatigue while enhancing joint performance, we examined the effects of one bout of a short-duration isometric MVC and neuromuscular electrical stimulation (NMES). Methods: In the first experiment, the optimal duration of NMES for inducing twitch potentiation of the quadriceps femoris muscle was determined, which was found to be 5 s. Then in the second experiment, 13 subjects performed maximal voluntary isokinetic concentric knee extensions at 210 degrees s(-1) in the following sequence: before and immediately after each of the 3-, 5-, and 10-s MVCs and 5-s NMES of knee extension and 1, 3, and 5 min thereafter. Results: When the isometric MVC was used as a conditioning contraction, the maximal voluntary concentric torque was significantly enhanced at 1 and 3 mm after MVC only in the 5-s MVC trial (106.6% +/- 2.3% and 107.2% +/- 2.6% of the initial value, respectively) but not in the 3- and 10-s MVC trials. In the 5-s NMES trial, the voluntary concentric torque was significantly increased immediately after the conditioning contraction (105.1% +/- 2.2%) as well as 1 and 3 min thereafter (107.5% +/- 3.3% and 107.8% +/- 2.7%, respectively). Conclusions: These results suggest that conditioning contraction of around 5 s, performed with isometric MVC or NMES, can be a modality to enhance dynamic voluntary joint performance, with the latter having a more immediate effect.

Purpose: The purpose of the present study was to examine a hypothesis that the musculotendinous behavior during a propelling action with a countermovement can be altered by a single practice session through modulation of neuromuscular activities. Methods: Eight males performed unilateral maximal plantarflexion with (CMJ) and without (noCMJ) countermovement before and after a practice consisting of six sets of three repetitions of unilateral CMJ exercises. Measurements included EMG activities of the triceps surae and tibialis anterior muscles and the fascicle behavior of the gastrocnemius by ultrasonography, and impulse was calculated from the force-time data. The change in tendon length was also estimated. Results: The impulse in CMJ increased after the practice, but that in noCMJ did not. After the practice, the magnitude of fascicle lengthening and shortening in CMJ decreased, which was accompanied by an increase in tendon shortening without change in the ankle joint range of motion. The time lag from the onset of reaction force to that of EMG activities of the triceps surae muscles was shortened after the practice. Conclusions: The results support the hypothesis and indicate that, as a neural modulation through a single practice, the muscle-tendon unit behavior during CMJ can be optimized to improve the performance. © 2012 by the American College of Sports Medicine.

This study aimed to clarify the influence of the intensity of a conditioning contraction on subsequent isometric twitch and maximal voluntary concentric torques. Subjects (n = 12 men) performed voluntary isometric plantar flexion for six seconds as a conditioning contraction, at intensities of 40%, 60%, 80% and 100% of a maximal voluntary isometric contraction (MVIC). Before and immediately after the conditioning contraction, isometric twitch and maximal voluntary concentric (180 degrees/s) plantar flexion torques were determined. Surface electromyograms were recorded from the triceps surae muscles and M-wave amplitudes and root-mean-square values of the electromyographic signals (RMSEMG) were calculated. The isometric twitch torque increased significantly after conditioning contraction at all intensities (P &lt; 0.05), whereas maximal voluntary concentric torque increased significantly only at 80% and 100% MVIC conditions (P &lt; 0.05). It is concluded that during a six second conditioning contraction, the effect of the intensity of a conditioning contraction on subsequent torque development is different between an isometric twitch and maximal voluntary concentric contractions, with the latter being less affected. (c) 2012 Elsevier Ltd. All rights reserved.

Asians seem to have less skeletal muscle mass (SMM) than other ethnic groups, but it is not clear whether relative SMM, i.e., SMM / height square or SMM to fat-free mass (FFM) ratio, differs among different ethnic groups at the same level of body mass index (BMI).
To compare the SMM to fat-free mass (FFM) ratio as well as anthropometric variables and body composition among 3 ethnic groups.
Three hundred thirty-nine Japanese, 343 Brazilian, and 183 German men and women were recruited for this cross-sectional study.
Muscle thickness (MTH) and subcutaneous fat thickness (FTH) were measured by ultrasound at nine sites on the anterior and posterior aspects of the body. FTH was used to estimate the body density, from which fat mass and fat-free mass (FFM) was calculated by using Brozek equation. Total SMM was estimated from ultrasound-derived prediction equations.
Percentage body fat was similar among the ethnic groups in men, while Brazilians were higher than Japanese in women. In German men and women, absolute SMM and FFM were higher than in their Japanese and Brazilians counterparts. SMM index and SMM:FFM ratios were similar among the ethnic groups in women, excluding SMM:FFM ratio in Brazilian. In men, however, these relative values (SMM index and SMM:FFM ratio) were still higher in Germans. After adjusting for age and BMI, the SMM index and SMM:FFM ratios were lower in Brazilian men and women compared with the other two ethnic groups, while the SMM index and SMM:FFM ratios were similar in Japanese and German men and women, excluding SMM:FFM ratio in women.
Our results suggest that relative SMM is not lower in Asian populations compared with European populations after adjusted by age and BMI.

The present study investigated the effect of movement frequencies on the behavior of fascicles and tendons of synergistic muscles. Seven male subjects performed ankle bending (calf-raise) exercises at four movement frequencies (1.33, 1.67, 1.84, and 2.00 Hz), performed with an identical range of ankle joint motion. The fascicle and tendon behavior of medial gastrocnemius (MG) and soleus (SOL) was measured by ultrasonography while kinematic and kinetic parameters of the ankle were recorded. The torque of ankle joint was larger at higher exercise frequencies. The length change of muscle decreased and that of tendon increased at higher frequencies both for MG and for SOL, with no significant inter-muscle differences in the relative changes of muscle or tendon lengths to that of MTU. Changes of pennation angles and electromyographic activities as a function of movement frequency were also comparable for MG and SOL. These results suggest that under a stretch-shortening cycle action, the muscle-tendon interaction is altered by the movement frequency toward greater use of tendon elastic energy to provide greater MTU power at a higher frequency. Results also suggest that the movement frequency dependence of fascicle and tendon behavior is comparable between MG and SOL.

The motor nerve of the bi-articular rectus femoris muscle is generally split from the femoral nerve trunk into two sub-branches just before it reaches the distal and proximal regions of the muscle. In this study, we examined whether the regional difference in muscle activities exists within the human rectus femoris muscle during maximal voluntary isometric contractions of knee extension and hip flexion. Surface electromyographic signals were recorded from the distal, middle, and proximal regions. In addition, twitch responses were evoked by stimulating the femoral nerve with supramaximal intensity. The root mean square value of electromyographic amplitude during each voluntary task was normalized to the maximal compound muscle action potential amplitude (M-wave) for each region. The electromyographic amplitudes were significantly smaller during hip flexion than during knee extension task for all regions. There was no significant difference in the normalized electromyographic amplitude during knee extension among regions within the rectus femoris muscle, whereas those were significantly smaller in the distal than in the middle and proximal regions during hip flexion task. These results indicate that the bi-articular rectus femoris muscle is differentially controlled along the longitudinal direction and that in particular the distal region of the muscle cannot be fully activated during hip flexion.

The purpose of this study was to determine in vivo moment arm lengths (MAs) of three elbow flexors at rest and during low- and relatively high-intensity contractions, and to examine the contraction intensity dependence of MAs at different joint positions. At 50 degrees,80 degrees and 110 degrees of elbow flexion, MAs of the biceps brachii, brachialis and brachioradialis were measured in 10 young men using sagittal images of the right arm obtained by magnetic resonance imaging, at rest and during 20% and 60% of isometric maximal voluntary elbow flexion. In most conditions, MAs increased with isometric contractions, which is presumably due to the contraction-induced thickening of the muscles. This phenomenon was especially evident in the flexed elbow positions. The influence of the contraction intensities on the increases in MAs varied across the muscles. These results suggest that in vivo measurements of each elbow flexor MA during contractions are essential to properly examine the effects on the interrelationships between elbow flexion torque and individual muscle forces.

Introduction: In this study we aimed to compare the extent of twitch potentiation (TP) after voluntary contraction and percutaneous electrical stimulation of muscles (neuromuscular electrical stimulation: NMES) with various stimulation frequencies at equivalent target levels. Methods: Isometric knee extensions of 10 s were performed at a 40% maximal voluntary contraction level by voluntary or NMES conditioning contractions at 20, 40, and 80 HZ of the quadriceps femoris muscle. Twitch responses were elicited by stimulating the femoral nerve transcutaneously at supramaximal intensity. Results: NMES at 80 HZ induced significantly less TP (128.7 +/- 17.1%) than voluntary contraction (156.2 +/- 23.1%), whereas no statistical difference was found in TP among voluntary and 20- and 40-HZ NMES conditioning contractions (170.8 +/- 21.1% and 162.7 +/- 16.9% for 20- and 40-HZ NMES, respectively). Conclusion: Stimulation frequency of NMES determines whether NMES can induce TP comparable to that after voluntary contraction. Muscle Nerve 45: 110115, 2012

Purpose: To compare the effect of habitual recreational sports and exercise activity on age-related, site-specific muscle loss in young and old women in Japan.
Methods: Participants included 152 young (aged 20-35 years) and 157 old (aged 60-85 years) women who were classified into 4 subgroups on the basis of their habitual (more than once a week) sports and exercise activity: young active (n = 86), young inactive (n = 66), old active (n = 43), and old inactive (n = 114). Muscle thickness (MTH) and fat thickness (FTH) were measured by ultrasonography at 8 sites, with MTH expressed in terms relative to limb length (MTH/L) or height (MTH/Ht). Percent fat was estimated from FTH, and fat-free mass was calculated.
Results: Fat-free mass was similar between younger and older women and between active and inactive women. MTH/L in the quadriceps (P &lt; .001), abdomen (P &lt; .001), and triceps surae (P &lt; .05) was lower in the older women than in the younger women. In contrast, MTH/L in the hamstrings, subscapula, and biceps was higher (P &lt; .01) in the older women than in the younger women. Compared with the MTH of the young inactive women, the MTH of the young active women was greater (P &lt; .05) in 5 sites. Similarly, MTH/L in the quadriceps and triceps was higher (P &lt; .05) in the old active women than in the old inactive women. However, quadriceps MTH/L and abdomen MTH/Ht were still lower (P &lt; .001) in the old active women than in the young inactive women.
Conclusion: Age-related muscle loss remains site-specific in both active and inactive young and old women, even when habitual physical activity has an effect on muscle size.

PURPOSE: The present study aimed to develop an ultrasonographic method for estimating the cross-sectional area of the psoas major muscle. METHODS: The muscle cross-sectional area (CSA(MRI)) and thickness (MT(MRI)) of the psoas major muscle at L4-L5 on the right and left sides of the body were measured using magnetic resonance imaging in 11 healthy sedentary men age 21 to 25 yr. Ultrasonographic images were obtained at the corresponding sites where CSA(MRI) and MT(MRI) measurements were performed. From the ultrasonographic images, the thickness of the psoas major muscle (MT(US)) was analyzed on both sides of the body. RESULTS: The interclass correlation coefficient of MT(US) measurements performed on two separated days was 0.951 for the right side and 0.971 for the left side. CSA(MRI) was significantly correlated to MT(MRI) (r = 0.934 for the right side and r = 0.910 for the left side). There was no significant difference between MT(MRI) (4.68 ± 0.39 cm for the right side and 4.73 ± 0.39 cm for the left side) and MT(US) (4.67 ± 0.40 cm for the right side and 4.72 ± 0.43 cm for the left side). The MT(US) was significantly correlated to MT(MRI) (r = 0.979 for the right side and r = 0.980 for the left side) and CSA(MRI) (r = 0.947 for the right side and r = 0.916 for the left side). CONCLUSION: The current results indicate that the psoas major muscle thickness determined by the ultrasonographic method is useful for estimating the cross-sectional area of the psoas major muscle.

In this study, we examined applicability of existing equations to predicting the body surface area (BSA) of children, and newly developed prediction equations for the BSA of children. BSA of 87 children of both genders (7 ∼ 12 yr) was determined by the three-dimensional photonic image scanning (3DPS), which was used as reference. BSA predicted using existing equations yielded overestimation or underestimation and/or a systematic error with respect to the reference. BSA prediction equations for boys and girls were developed using height and body mass as independent variables for the validation group and cross-validated for another group. The standard errors of estimation of the prediction equations were 105 cm 2 (0.9 %) for boys and 158 cm 2 (1.4 %) for girls. In the cross-validation group, there was no significant difference between the predicted and measured values without systematic errors. These findings indicate that existing equations cannot accurately predict BSA of children, and that the newly developed prediction equations are capable of predicting BSA of children with adequate accuracy.

The present study examined spatial changes in the muscle activation pattern with different contraction intensity using magnetic resonance imaging (MRI). Transverse relaxation time (T2)-weighted MRI was used to acquire 22 axial slices, which covered the entire medial gastrocnemius muscle, before and immediately after seven sets of 10 plantarflexions with loads that were approximately 20 and 60% of their one-repetition maximum, respectively. Reconstructions of the activated regions from MR images revealed the following: (1) the muscle activation determined by MRI correlated significantly (P &lt; 0.05) with the results of electromyography; (2) the activated area distribution increased with increasing force levels; and (3) differential activation between 20 and 60% load was distributed in a spatially non-uniform manner within the muscle, and some regions indicated reduced activity. These results indicate that at submaximal contraction intensity, activation does not necessarily increase in the whole muscle with increase in contraction intensity.

The purpose of this study was to compare the age-related muscle loss in both the appendicular and trunk regions in 207 Japanese and 111 German men aged 20-62 years. Ultrasound-measured muscle thickness (MTH) was taken at eight sites from the anterior and posterior aspects of the body, and the MTH was expressed in terms relative to limb length (MTH/L) or standing height (MTH/Ht). In both the Japanese and Germans, age was correlated with quadriceps MTH (Japanese, r = -0.347; Germans, r = -0.292; both P&lt;0.01) and abdomen MTH (Japanese, r = -0.300, P&lt;0.01; Germans, r = -0.232; P&lt;0.05). On the other hand, hamstring MTH was correlated with age in the Japanese (r = -0.188, P&lt;0.01), but not in the Germans (r = 0.100). There were no significant correlations between age and other limb (i.e. triceps surae MTH/L, Japanese, r = 0.04; Germans, r = 0.05) and trunk sites (subscapula MTH/Ht, Japanese, r = -0.09; Germans, r = -0.02). In conclusion, age-related skeletal muscle loss was strongly observed in the quadriceps and abdominal sites in both the Japanese and German men, although the rate of regular physical activity was different between the two groups.

Findings from animal experiments are sometimes contradictory to the idea that the tendon structure is a simple elastic spring in series with muscle fibers, and suggest influence of muscle contraction on the tendon mechanical properties. The purpose of the present study was to investigate the influence of muscle contraction levels on the force-length relationship of the human Achilles tendon during lengthening of the triceps surae muscle-tendon unit. For seven subjects, ankle dorsiflexion was performed without (passive condition) and with contraction of plantar flexor muscles (eccentric conditions, at 3 contraction levels) on an isokinetic dynamometer. Deformation of the Achilles tendon during each trial was measured using ultrasonography. The Achilles tendon force corresponding to the tendon elongation of 10 mm in the passive condition was significantly smaller than those in the eccentric conditions (p &lt; 0.05 or p &lt; 0.01). Within the eccentric conditions, the Achilles tendon force corresponding to the tendon elongation of 10 mm was significantly greater in the maximal contraction level than those in submaximal eccentric conditions (p &lt; 0.05 or p &lt; 0.01). In addition, the tendon stiffness was greater in higher contraction levels (p &lt; 0.05 or p &lt; 0.01). Present results suggest that the human tendon structure is not a simple elastic spring in series with muscle fibers. (c) 2011 Elsevier Ltd. All rights reserved.

The purpose of this study was to highlight the issues related to thickness-based muscle size evaluation that is commonly done in :field studies. The cross-sectional area, thickness (the vertical distance from the upper end of the elbow flexors to that of the humerus) and width (the horizontal distance from the left to the right end of the elbow flexors) of the elbow flexors at levels from the reference site (60% of the upper arm length from the acromial process of the scapula to the lateral epicondyle of the humerus) to 5 cm distal to it were determined in 11 young men using magnetic resonance imaging, both at rest and during isometric elbow flexion at 30% of maximal voluntary contraction. During 30% of maximal voluntary contraction, the thickness increased but the width decreased at each measurement site compared with those at rest. This was possibly due to difference in muscle slackness between both conditions. The correlation coefficients between the thickness and cross-sectional area for the elbow flexors were significantly lower at rest (r=0.551-0.856) than during 30% of maximal voluntary contraction (r=0.711-0.922). The present findings indicate that the thickness-based muscle size measurement at rest includes errors owing to the slackness of the resting muscles. J Physiol Anthropol 30(4): 169-174, 2011 http://www.jstage.jst.go.jp/browse/jpa2 [DOI: 10.2114/jpa2.30.169]

The purpose of the present study was to examine the effects of wearing a graduated elastic compression (EC) stocking, with different pressure profiles during a fatiguing calf-raise exercise session, on the torque generating capacity after exercise. Fourteen subjects performed 15 sets of 10 repetitions of calf-raise exercise, wearing one of three stockings of different compression pressure profiles: two kinds of EC stockings (one (EC30) with 30 mm Hg at the ankle, 21-25 mm Hg at the calf, and 10 mm Hg below the knee, and the other (EC18) with 18, 12-14, and 7 mm Hg at the same regions, respectively) and a non-EC sport stocking as a control (CON). Before and after the exercise, torque and electromyographic (EMG) signals of medial gastrocnemius and soleus muscles were recorded during an evoked triplet contraction and the maximal voluntary contraction (MVC). All stockings had no effect on the decline of the MVC torque whereas the reduction of the evoke triplet torque in EC30 stocking condition was significantly smaller compared with that in CON (-6.4 +/- 8.5% for EC30 and -16.5 +/- 9.0% for CON, P &lt; 0.05). The reduction of the mean power frequency of EMG during MVC in the EC30 condition was significantly smaller than that in CON (-4.4 +/- 10.9 Hz for EC30 and -18.7 +/- 7.9 Hz for CON, P &lt; 0.05). These results suggest that the EC stocking with adequate pressure at the calf region relieves muscle fatigue of the triceps surae induced by calf-raise exercise. (C) 2010 Elsevier Ltd. All rights reserved.

The purpose of this study was to compare the extent of twitch potentiation (TP) after stimulated or voluntary contractions at identical intensities for the human knee extensor muscles. Isometric knee extensions of 10 s. were performed at 20%, 40%, and 60% of maximal voluntary contraction (MVC) torque level, through percutaneous electrical stimulation of the quadriceps at 80 Hz or voluntary contraction. Twitch responses were evoked by stimulating the femoral nerve percutaneously with supramaximal intensity. The extent of TP after the stimulated contraction was greater than that after the voluntary contraction at the 20% MVC torque level, whereas a stimulated contraction induced a smaller extent of TP than did a voluntary contraction at contraction intensities higher than 40% MVC. We suggest that this contraction intensity dependence of differences in TP after stimulated and voluntary isometric conditioning contractions is responsible for differences in the recruitment pattern of motor units during the conditioning contractions. Muscle Nerve 43: 360-366, 2011

We investigated the relationship between age and muscle size in both the appendicular and trunk regions of 1507 Japanese men and women aged 20 to 95 years. Seven hundred twenty-two men (young [aged 20-39 years], n = 211; middle-aged [aged 40-59 years], n = 347; and old [aged 6095 years], n = 164) and 785 women (young, n = 207; middle-aged, n = 341; and old, n = 237) were recruited for this cross-sectional study. Muscle thickness (MTH) and subcutaneous fat thickness (FTH) were measured by ultrasound at 8 sites on the anterior and posterior aspects of the body. MTH was expressed in terms relative to limb length (MTH/L) or height (MTH/Ht). Percent body fat was estimated from FTH, and fat-free mass (FFM) was calculated. In men, a graded decrease in FFM was found in all age groups. In women, FFM was similar in the young and middle-aged groups, but was lower in the oldest group. Age was significantly and inversely correlated with FFM in men (r = -0.358, p &lt; 0.01), but not in women (r = -0.08). On the other hand, age was strongly and inversely correlated with quadriceps MTH/L (men, r = -0.529; women, r = -0.489; both p &lt; 0.001) and abdomen MTH/Ht (men, r = -0.464; women, r = -0.446; both p &lt; 0.001) in both men and women, while there were only weak correlations between age and other lower limb and trunk sites. Our results indicated that sarcopenia is observed as a site-specific loss of skeletal muscle mass, especially for the quadriceps and abdominal muscles, in Japanese men and women aged 20 to 95 years.

In the present study, we examined the relationships between muscle volume and joint torque for the elbow flexors and extensors in young and elderly individuals, with the aim of evaluating age effects on these relationships. The participants were 45 young (27 men and 18 women aged 20-37 years) and 51 elderly (19 men and 32 women aged 60-77 years) individuals. The joint torques developed during isometric maximal voluntary elbow flexion and extension were measured using a torque meter. The muscle volumes of the elbow flexors and extensors were determined by magnetic resonance imaging. For the elbow flexors, joint torque was significantly correlated with muscle volume in both young and elderly individuals (r=0.564-0.872). There were also significant correlations between muscle volume and joint torque for the elbow extensors in elderly men and women as well as in young men and women (r=0.715-0.826). None of the y-intercepts of the regression lines between muscle volume and joint torque were significantly different from zero. Furthermore, no significant age or gender effects on the joint torque per muscle volume of the elbow flexors and extensors were observed. The present results suggest that muscle volume is a main determinant of joint torque regardless of age and gender, for both muscle groups.

Miyamoto, N, Kanehisa, H, Fukunaga, T, and Kawakami, Y. Effect of postactivation potentiation on the maximal voluntary isokinetic concentric torque in humans. J Strength Cond Res 25(1): 186-192, 2011-The purpose of this study was to examine whether postactivation potentiation (PAP) influences dynamic torque development in humans. Nine recreationally active men performed sets of 3 maximal isokinetic concentric plantar flexions at 180 degrees/second in the following sequence: before and immediately (5 seconds) after a 10-second maximal voluntary contraction (MVC) and then every 1 minute until the 5-minute point, followed by 1 more stimulation at the 10-minute point. Twitch responses were recorded before every set of 3 concentric contractions to examine whether the PAP exists. The twitch and concentric torques were potentiated at 0 through 5 minutes and 1 through 3 minutes post-MVC, respectively (p &lt; 0.05), whereas there was no significant difference in concentric torque in the control (without MVC) condition (p &gt; 0.05). For electromyographic signals during concentric contractions, muscle activity of the medial gastrocnemius was significantly depressed only immediately after the conditioning MVC (p &lt; 0.05). These results indicate that a brief maximal voluntary isometric contraction enhances voluntary dynamic performance through PAP, within proper recovery interval. From a practical point of view, in sports activities we suggest undertaking PAP through high-intensity contractions 1 to 3 minutes before voluntary ballistic or plyometric actions for improved performance.

The purpose of this study was to test the hypothesis that the musculotendon moment arm length is affected by the muscle anatomical cross-sectional area. The moment arm length of the triceps brachii (TB) muscle at 30 degrees, 50 degrees, 70,degrees 90 degrees, 110 degrees elbow flexion positions was measured in sagittal magnetic resonance images (MRI) of 18 subjects as the perpendicular distance between the center of the pulley of the humerus to the line through the center of the TB tendon. The moment arm increased as the elbow flexion angle decreased, from 1.74 +/- 0.13 cm at 110 degrees to 2.39 +/- 0.14 cm at 30 degrees. The maximal anatomical cross-sectional area of the TB muscle was significantly correlated with the moment arms at all joint positions (r=0.545-0.803, p &lt; 0.05). Furthermore, the circumference of the upper arm was also significantly correlated with the moment arms at all joint positions, except for 70 (r=0.504-0.702, p &lt; 0.05). These results indicate that the moment arm length of the TB muscle is affected by the muscle anatomical cross-sectional area. (C) 2010 Elsevier Ltd. All rights reserved.

Exposure to unaccustomed eccentric exercise causes muscle damage. Popping sarcomere theory [1] has been proposed and assumed that eccentric contraction-induced muscle damage predominantly occurs at muscle length on the descending limb of the force-length relationship. This study investigated changes in the mechanical properties following maximum effort eccentric exercise at systematically different muscle lengths for the human ankle dorsiflexors. The results of this study showed that the eccentric exercise of the ankle dorsiflexors decreased the peak torque, shifted the optimal joint angle towards longer muscle length without changes in the level of muscle activation. However, no difference in the shift of the optimal ankle joint angle was observed between the groups that performed eccentric exercise at long muscle length (ECC_L) and at short muscle length (ECC_S). In conclusion, the muscle length at which the eccentric exercise was performed did not produce differential effects on the neuro-mechanical properties of in-vivo human ankle dorsiflexors, and thus the popping sarcomere theory might not be the sole mechanism to account for the eccentric contraction-induced optimal muscle length change.

The present study examined the age-related changes in muscle thickness (MT) and volume (MV) of elbow flexors and developed a prediction equation of the MV based on the MT applicable to men and women with a wide range of age. The MT and MV were determined from a single ultrasonographic image and multiple magnetic resonance imaging scans, respectively, in 72 men and 75 women aged 19-77 year. As a result of examining the age-MT and age-MV relationships by calculation of partial correlation coefficients with the control variable of gender, MV was decreased with aging whereas the corresponding decline in MT was not significant. The subjects were randomly separated into either a validation (38 men and 42 women) or a cross-validation (34 men and 33 women) group, and a multiple regression equation to estimate MV using not only MT but also upper arm length (L), age and gender as independent variables [MV (cm(3)) = 60.8 x MT (cm) + 6.48 x L (cm) - 0.709 x age (year) + 51.4 x gender (0 women, 1 men) - 187.4] was validated and cross-validated. Thus, the prediction equation for MV of elbow flexors newly developed was shown to be applicable to men and women with a wide range of age.

The purpose of this study was to determine the interindividual variability of the upper and lower limb muscle size in young men. Subjects were 655 Japanese men aged 18-39 years. They were sedentary and mildly to highly active individuals, including college athletes of various sports. Muscle thicknesses at each of the anterior and posterior portions of the upper arm, thigh, and lower leg were measured using B-mode ultrasonography. Interindividual variability of muscle thickness was evaluated by coefficients of variation (CVs). The CVs of muscle thicknesses were found to be in the order of upper arm posterior (17.7%), thigh anterior (14.8%), thigh posterior (12.6%), upper arm anterior (12.2%), lower leg anterior (9.8%), and lower leg posterior (9.4%). The CVs were significantly different between each pair of measurement sites except for those of upper arm anterior-thigh posterior and lower leg anterior-posterior. These differences remain significant even when the muscle thicknesses were normalized to the segment length. The observed differences in the size variability can be interpreted as muscle-related differences in hypertrophic responsiveness to resistance training. The muscle-dependent size variability may be related to the differences in the fiber-type composition and/or muscle usage in daily life among examined muscle groups. © 2009 Wiley-Liss, Inc.

The purpose of this study was to investigate changes in ankle joint stiffness and the associated changes in the gastrocnemius muscle and tendon due to static stretching. Seven healthy male participants lay supine with the hip and knee joints fully extended. The right ankle joint was rotated into dorsiflexion from a 30 degrees plantar flexed position and the torque measured by a dynamometer. The ankle joint was maintained in a dorsiflexed position for 20 min (static stretching of the calf muscles). We performed surface electromyography of the medial and lateral gastrocnemii, the soleus, and the tibialis anterior of the right leg to confirm no muscle activity throughout static stretching and the passive test (passive dorsiflexion). During static stretching, the ankle joint angle and elongation of the gastrocnemius were recorded by goniometry and ultrasonography, respectively. Tendon elongation of the gastrocnemius was calculated based on the changes in the ankle joint angle and muscle elongation. In addition, the relationships between passive torques and ankle joint angles, and elongation of muscle and tendon, were examined before and after static stretching. The ankle dorsiflexion angle and tendon elongation increased significantly by 10 min after the onset of static stretching, while there was no further increase in muscle length. In addition, ankle dorsiflexion angle and tendon elongation at an identical passive torque (30 N center dot m) increased significantly (from 24 +/- 7 degrees to 33 +/- 5 degrees and from 17 +/- 2 mm to 22 +/- 1 mm, respectively) after static stretching. However, muscle elongation was unchanged. In conclusion, the current results suggest that an increase in the ankle joint dorsiflexion angle due to static stretching is attributable to a change in tendon not muscle stiffness.

OBJECTIVE: the present study examined which of muscle volume (MV) and cross-sectional area (CSA) is appropriate for evaluating the relation with elbow flexor muscle strength in young and elderly individuals. METHODS: the subjects were 52 young (20-34 year; 30 men and 22 women) and 51 elderly individuals (60-77 year, 19 men and 32 women). The MV and maximal anatomical CSA (ACSA) of elbow flexors were determined by magnetic resonance imaging. The torque developed during maximal voluntary contraction of isometric elbow joint flexion was converted to force by dividing it by the forearm length of each subject. RESULTS: torque was significantly correlated with MV in young and elderly individuals (r = 0.564-0.926). Similarly, force was also significantly correlated with ACSA in each of them (r = 0.637-0.906). However, the y-intercepts of the regression lines for the ACSA-force relationship in young men and women were significantly higher than zero. There was no age effect on torque per MV, whereas force per ACSA was significantly higher in young adults than in elderly individuals. CONCLUSION: for elbow flexors, MV compared to ACSA is appropriate for evaluating the size-strength relationship and the existence of age-related difference in muscle strength per size.

The present study examined how muscle cross-sectional area (CSA) indices determined at rest and during maximal voluntary contraction (MVC) are related to muscle strength in middle-aged and elderly individuals (22 men and 36 women, 51-77 years). The muscle thickness (MT) of elbow flexors and circumference (C) at the level 60% distal to the upper arm was measured by ultrasonography and a measuring tape, respectively, both at rest and during isometric MVC of elbow flexion. The muscle strength (F) of elbow flexors was calculated by dividing the torque developed during MVC by the forearm length of each subject. The product of MT and C (MTxC) and the square of MT (MT) were defined as the muscle CSA indices. The F was significantly correlated with MTxC during MVC (r = 0.905, p < or = 0.001) and at rest (r = 0.778, p < or = 0.001), with the former relationship significantly stronger than the latter (p < or = 0.001). Similarly, F was significantly correlated with MT both during MVC (r = 0.896, p < or = 0.001) and at rest (r = 0.780, p < or = 0.001), and there was also a significant difference between the correlation coefficients (p < or = 0.01). These findings show that, in middle-aged and elderly individuals, muscle strength is more closely related to muscle CSA indices during MVC than at rest. It is concluded that the present muscle CSA indices taken during MVC enable easy and practical evaluation of the muscle strength per size of elbow flexors in middle-aged and elderly individuals.

To investigate the relationship between fascicle behavior and joint torque, the fascicle behavior of the triceps surae during isometric and eccentric (30 and 60 deg/s) plantar flexion by maximal voluntary and submaximal electrical activation (MVA and SEA) was measured by real-time ultrasonography. Eccentric torque at 30 and 60 deg/s was significantly higher than isometric torque under SEA, but not under VIVA. However, fascicle length did not significantly differ between isometric and eccentric trials under either condition. Therefore, the difference in developed torque by VIVA and SEA cannot be explained by fascicle behavior. Under both MVA and SEA conditions, eccentric torque at 30 and 60 deg/s was equivalent. Similarly, fascicle lengthening velocities at 30 and 60deg/s did not show any significant difference. Such fascicle behavior can be attributed to the influence of tendinous tissue and pennation angle, and lead to a lack of increase in eccentric torque with increasing angular velocity.

This study compared the postactivation potentiation of the medial gastrocnemius (MG) and soleus muscles by using mechanomyography (MMG). Twitch responses were evoked by stimulating the posterior tibial nerve with supramaximal intensity before and after a 10-s maximal voluntary plantar flexion, and potentiation of each muscle was evaluated by peak-to-peak amplitude of the MMG signal. The MG showed greater potentiation than the soleus, reflecting the reported fiber type composition of these muscles. This result points to the possibility that one can delineate contrasting responses of synergist muscles to postactivation potentiation by this method.

The present study examined whether a sit-to-stand score can be related to the force-generating capacity of knee extensor muscles. Fifty-seven subjects (28 men, 63.0+/-7.8 yrs, and 29 women, 64.2+/-7.5 yrs, means+/-SDs) performed a 10-repeated sit-to-stand test as fast as possible, on a steel molded chair. The time taken (T(sit-stand)) was measured with a manual stopwatch. The leg length (L), defined as the distance from the great trochanter of the femur to the malleolus lateralis, was measured using a tape. A power index of the test (P(sit-stand)) was calculated by using the following equation: P(sit-stand)=(L-0.4) x body mass x g x 10/T(sit-stand). The cross-sectional area of the quadriceps femoris muscle (CSA(KE)) and the maximal voluntary isometric knee extension force (F(KE)) were measured using MRI and a static myometer, respectively. There was no significant correlation between T(sit-stand) and each of CSA(KE) and F(KE). On the other hand, the P(sit-stand) was highly correlated with CSA(KE) and F(KE), even after the influence of body mass and L was statistically eliminated. These results indicate that P(sit-stand), derived from three variables of body mass, leg length, and time taken for a sit-to-stand test, can be a useful index to assess the force-generating capacity of the knee extensor muscles of elderly individuals.

筋疲労を伴う動的運動中の協働筋の筋腱動態について成人男性8名(平均22.7±1.4歳)を被験者として、関節トルクやパワーの変化と筋腱動態の変化の関係と協働筋間で比較検討した。被験者に疲労課題として2秒に1回のテンポによるカーフレーズ運動を200回(20回×10セット)行い、運動中の腓腹筋内側頭(MG)とヒラメ筋(SOL)の筋束をBモード超音波法により撮像した。その結果、疲労課題後に等尺性足関節底屈トルクは有意に低下し、運動中の足関節トルクとパワーは変化しなかった。同一の足関節角度における筋束長は最初のセットに比べ最後のセットで有意に長くなり、筋束の伸張・短縮速度が有意に低下した。筋腱複合体長変化に対する筋長変化と腱長変化の割合は、最後のセットにおいてMG・SOL共に高くなる傾向がみられた。以上より、疲労課題実施中の筋腱動態と筋腱相互作用を通じて関節で発揮されるトルクやパワーが維持される機序が働いていることが推察され、MG・SOLは筋腱動態を変えることで関節トルクとパワーを維持していることが示唆された。

STUDY DESIGN: Experimental laboratory study.
OBJECTIVES: We tested the hypothesis that the muscle fibers and the connective tendinous structures, combined in series, provide the resistance to passive joint movement at the ankle. We also determined the relative association between passive joint torque and each of these 2 elements.
BACKGROUND: The reason for individual variation in joint flexibility or tightness is not clearly understood, but the influence of musculotendinous stiffness has been inferred.
METHODS AND MEASURES: Each of the subjects (6 women and 6 men) was seated with the right knee extended and right ankle positioned at a 30 degrees, 20 degrees, 10 degrees, 0 degrees, -10 degrees, -20 degrees, and -30 degrees (0, neutral position, positive values reflecting plantar flexion) angle while passive plantar flexion torque was measured. The distal muscle-tendon junction of the medial gastrocnemius was visualized by ultrasonography, and its positional change was defined as muscle belly length change, The whole muscle-tendon unit length change was estimated from joint angle changes, from which Achilles tendon length change was estimated.
RESULTS: Both the muscle belly and tendon were significantly elongated as the ankle was dorsiflexed (at 0 degrees the mean +/- SD muscle belly elongation was 10.3% +/- 1.8%, and the tendon elongation was 2.8% +/- 1.2%, of the initial length of their respective structures measured at 30 degrees of ankle plantar flexion), from which stiffness indices were determined both for muscle belly and tendon. The passive torque at 0 degrees, -10 degrees, -20 degrees, and -30 degrees was significantly correlated with the stiffness indices of the Achilles tendon (at 0 degrees, r(2) = 0.70 and 0.62 for overall and specific stiffness, respectively; P&lt;.05). A tendon stiffness index, separately obtained from tendon lengthening during maximal isometric contraction, was also correlated with passive ankle plantar flexion torque at 0 degrees, -10 degrees -20 degrees, and -30 degrees (at 0 degrees, r(2) = 0.76, P&lt;.05), The specific stiffness index of the muscle belly was correlated (r(2) = 0.47, P&lt;.05) with the passive ankle plantar flexion torque at 0 degrees, but its overall stiffness index was not (r(2) = 0.32, P&gt;.05).
CONCLUSION: Results suggest that extensibility of the muscle-tendon unit of the Achilles tendon for the most part is related to passive ankle plantar flexion joint torque.

Ultrasonography was used to directly measure in vivo fascicle behavior of the medial gastrocnemius (MG) and soleus (SOL) muscles while the subjects (n = 6 men) performed maximal voluntary concentric and eccentric plantar flexions at 60, 120, 180 and 240 deg/s. Fascicle shortening and lengthening velocities of MG, obtained from fascicle length changes over time, were significantly higher than those of SOL at +/- 120, +/- 180 and +240 deg/s, possibly reflecting physiological and mechanical differences between these muscles. On the other hand, the effective fascicle shortening and lengthening velocities, defined as the velocities in the longitudinal direction of muscle belly, were not significantly different between MG and SOL. This could be due to difference in fascicle architecture and/or the existence of mechanical linkages between these muscles. Moreover, when the contribution of tendinous tissues to muscle-tendon complex length change was determined from fascicle length, pennation angle, moment arm and joint angle, it accounted for approximately 50% in both concentric and eccentric trials, but showed considerable intra-subject variations. This result quantifiably demonstrates the importance of tendinous tissues in isokinetically controlled joint movements. (C) 2006 Elsevier Ltd. All rights reserved.

The impact force which runners receive passively during running reaches approximately 1.5〜5.0 times the body weight. The joint movements of lower extremity have strategy which absorbs the impact force. In addition, shoes have an important role of absorbing the impact force. This study investigated the relationship between the impact force and joint movements wearing different shoes. Eight subjects ran at 3.5m/s wearing 3-types of shoes with different shock-absorbing capacities. Shoes with thicker outer-sole were defined as shoes with higher shock-absorbing. GRF, joint angle, joint angular velocity, sole angle which is angle between foot and ground at touch down, and time of maximum joint angular velocity were sampled and computed. Time of GRF first peak and loading rate were longer and smaller significantly and knee joint angle at touchdown tended to be smaller when runners wore shoes with higher shock-absorbing. It was suggested that shoes with higher shock-absorbing attenuated the impact to the body and influenced running motion.

The present study aimed to examine the effect of pennation angle on the force per cross-sectional area for elbow extensor muscles in strength-trained athletes. A total of 52 male bodybuilders (n = 32) and Olympic weightlifters (n = 20) did maximal isometric elbow extension on an isokinetic dynamometer. Muscle cross-sectional area (CSA) and muscle-fiber pennation angle (PA) of the triceps brachii muscles were measured by ultrasonography. Bodybuilders had significantly greater isometric elbow extension force (F), CSA and PA than weightlifters. The ratio of force to CSA (F/CSA) of bodybuilders was significantly lower than that of weightlifters. A significant positive correlation was observed between CSA and PA in both groups (r = 0.832, P &lt; 0.001, and r = 0.682, P &lt; 0.001, for bodybuilders and weightlifters, respectively). The F/CSA was negatively correlated to PA both for bodybuilders (r = -0.408, P &lt; 0.05) and weightlifters (r = -0.465, P &lt; 0.05). Thus present study indicates that the larger pennation angle is associated with the lower force relative to muscle CSA in strength-trained athletes.

The present study aimed i) to establish an index of muscle cross-sectional area (CSA) based on muscle thickness and circumference through a comparison with muscle CSA determined by magnetic resonance imaging (MRI), and ii) to examine the relationships between muscle strength and the index determined at rest and during the maximal isometric contraction. The muscle CSA of elbow flexors at 60% of the upper arm length (CSA(60)) and the maximal CSA of elbow flexors (CSA(max)) were measured using MRI in 26 men and 8 women. The muscle thickness (MT) of elbow flexors and the circumference (C) of upper arm at 60% of the upper arm length were measured using ultrasonography and anthropometry, respectively, in 29 men and 9 women. The measurements of MT and C were performed in the resting (MTr and C-r) and contracted condition (MTm and C-m), where the subjects performed maximal voluntary contraction (MVC) of isometric elbow joint flexion. The torque developed during MVC was converted into the muscle force (F) of elbow flexors. The MTr X C-r was significantly correlated both with CSA(60) and CSA(max) (P &lt; 0.001). The F was significantly correlated with MTm X C-m (r = 0.847, P &lt; 0.001) and MTr X C-r (r = 0.839, P &lt; 0.001). However, stepwise multiple regression analysis selected only MTm X C-m as a significant contributor for estimating F. The present study indicates that MT X C reflects muscle CSA, and can be an index for assessing muscle CSA. In addition, the findings obtained here showed a possibility that MT X C during MVC is more closely related to F than that at rest.

The present study investigated the differences between the human medial gastrocnemius (MG) and soleus (SOL) muscles in length changes of muscle fascicles and tendinous tissues during twitch contraction induced by an electrical nerve stimulus. Also, the time-course characteristics of twitch torque were related with changes in the length of muscle fascicles and tendinous tissues. No significant difference was observed between MG and SOL in contraction and half relaxation times of the changes in lengths and velocities of both muscle fascicles and tendinous tissues. The time-course of changes in twitch torque was nearly identical to that of the length of muscle fascicles and tendinous tissues. It was suggested that the behavior of MG and SOL during twitch contraction is practically similar in spite of their known physiological and architectural differences, and that the time-course of twitch torque is greatly influenced by the changes in the length of muscle fascicles and tendinous tissues. (c) 2006 Elsevier Ltd. All rights reserved.

論文

The present study tested the hypotheses that Achilles tendon forces during fast concentric actions do not differ between extended and flexed knee positions, and this phenomenon is attributable to the force-length characteristics and electromyograms (EMGs) of gastrocnemius muscle. Seven healthy men performed static and concentric plantarflexions at fully extended (K0) and 0.785 rad (45 degrees) Flexed (K45) knee positions with the maximal effort. In concentric actions, the angular velocities were set at 0.524 (slow) and 6.109 rad s(-1) (fast). Fascicle length of medial gastrocnemius (MG) was determined with ultrasonography. Surface EMGs of the MG were recorded luring each action. Achilles tendon force was calculated from the torque and moment arm of the tendon. Peak tendon forces in fast concentric actions were similar in KO and in K45, but those in static and slow concentric actions significantly (P &lt; 0.05) differed between :he two positions. When the tendon force peaked, the fascicle lengths in each action and fascicle velocities in both concentric actions were significantly (P&lt;0.05) greater in KO than in K45. The EMGs were significantly (P&lt;0.05) higher in KO than K45 during each action. The results suggest that (1) the difference in the tendon forces between the two positions can be explained by the force-length and -velocity Characteristics and the EMGs of the MG, and (2) the contribution of the MG to the tendon force in flexed knee positions is greater in concentric actions than expected from the results in static actions. (C) 2006 Elsevier Ltd. All rights reserved.

In this study we investigated the time course of length and velocity of muscle fascicles and tendinous tissues (TT) during isometric twitch contraction, and examined how their interaction relates to the time course of external torque and muscle fascicle force generation. From seven males, supra-maximal twitch contractions (singlet) of the tibialis anterior muscle were induced at 30 degrees, 10 degrees and -10 degrees plantar flexed positions. The length and velocity of fascicles and TT were determined from a series of their transverse ultrasound images. The maximal external torque appeared when the shortening velocity of fascicles was zero. The fascicle and TT length, and external torque showed a 10-30 ins delay of each onset, with a significant difference in half relaxation times at -10 degrees. The time course of TT elongation, and fascicle and tendinous velocities did not differ between joint angles. Curvilinear length-force properties, whose slope of quasi-linear part was ranged from -15.0 to -5.9N/mm for fascicles and 5.4 to 14.3N/mm for TT, and a loop-like pattern of velocity-force properties, in which the mean power was ranged from 0.14 to 0.80W for fascicles, and 0.14 to 0.81 W for TT were also observed. These results were attributed to the muscle-tendon interaction, depending on the slack and non-linearity of length-force relationship of compliant TT. We conclude that the mechanical interaction between fascicles and TT, are significant determinants of twitch force and time characteristics. (c) 2007 Elsevier Ltd. All rights reserved.

Purpose: To use muscle functional MRI (mfMRI) to compare activation levels within and among triceps surae (TS) muscles.
Materials and Methods: Seven healthy males performed five sets of 10 repetitions of a unilateral heel-raise exercise. T2-weighted images were obtained before and immediately after the exercise. Pixels that showed T2 greater than the mean + 1 SD of the region of interest (ROI) in pre-exercise images and lower than the mean + 1 SD of the ROI in post-exercise images were identified. The remaining T2 values in the post-exercise images were assigned to five categories indicated by color: red (highest level of activation), yellow, green, sky blue, and blue (lowest level of activation). The images were then used to construct three-dimensional (3D) images from which the volumes at each level of activation were determined.
Results: Within each of the TS muscles the % activated volumes with low and moderate levels of activation were larger than those with a high level of activation (P &lt; 0.05). The % activated volumes with a high level of activation were larger in the medial gastrocnemius than the soleus (Sol; P &lt; 0.05). The Sol had a larger % activated volume with a low level of activation than the lateral gastrocnemius (P &lt; 0.05). Each activation level was nonuniformly distributed along the length within each TS muscle.
Conclusion: There is substantial variation in the level of activation within and among the TS muscles; however. the activation level is mainly in the moderate to low range in all three muscles.

Seven hundred and eleven women and men (aged 3-94 years, including normal individuals and highly trained bodybuilders) were tested for the thickness and pennation angles of their triceps brachii (TB), vastus lateralis (VL), and gastrocnemius medialis (GM) muscles. The variations of muscle thickness and pennation angles were largest in TB (6-66 mm and 5-55 degrees), followed by VL (8-45 mm and 7-33 degrees) and GM (11-36mm and 12-33 degrees), and women showed smaller variations than men. These results suggest the existence of muscle- and gender-specificity in the variability of muscle dimensions. Significant positive correlations were observed between muscle thickness and pennation angles (r = 0.81, 0.61, and 0.56, for TB, VL, and GM, respectively), indicating that the size-dependence of the pennation angle is a general feature of pennate muscles.

The purpose of the present study is to determine whether muscle functional MRI (mfMRI) can be used to obtain three-dimensional (3-D) images useful for evaluating muscle activity, and if so, to measure the distribution of muscle activity within a medial gastrocnemius (MG) muscle. Seven men performed 5 sets of 10 repetitions of a calf-raise exercise with additional 15% of body-weight load. Magnetic resonance images were obtained before and immediately after the exercise. To threshold images, only those pixels showing transverse relaxation time (T2) greater than the mean+1 S.D. of the entire regions of interest (ROIs) in the preexercise image and T2 lower than the mean+1 S.D. of the entire ROIs in the postexercise image were identified. The survived pixels showing T2 are defined as active muscle. Those thresholded images were 3-D reconstructed, and this was used to determine area of active muscle along transverse, longitudinal and vertical axes. At the exercise level used in the present study, the percentage volume of activated muscle in the MG was 62.8 +/- 4.5%. There was a significant correlation between percentage volume of activated muscle and integrated electromyography (r=.78, P&lt;.05). Percentage areas of activated muscle were significantly larger in the medial than in the lateral region, in the anterior than in the posterior region and in the distal than in the proximal region (P&lt;.05). These results suggest that mfMRI can be used to evaluate the muscle activity and to determine intramuscular variations of activity within skeletal muscle. (C) 2006 Elsevier Inc. All rights reserved.

Approaches to understanding human muscle function through measuring in vivo muscle fiber behavior in humans are described briefly. Experimental results show the discrepancy between joint actions and muscle fiber behavior in many occasions, which complicates prediction of muscle mechanics from sole observations of joint actions. This is the result of muscle-tendon interaction during contraction, which is efficiently used during human movements.

The purposes of this study were 1) to quantify the volume of activated parts within a whole muscle and 2) to examine activated area distributions along the length of muscle. Seven male subjects performed five sets of 10 repetitions of a single-leg calf-raise exercise with the knee fully extended. Transverse relaxation time (T2)-weighted spin echo images were acquired before and immediately after the exercise. A range of pixels with a T2 greater than the mean + 1 SD of the region of interest (ROI) from the preexercise image and pixels with a T2 lower than the mean + SD of the ROI from the postexercise image were defined as "active" muscle. The active muscle images were three dimensionally reconstructed, from which the volume of the activated muscle was determined for individual triceps surae (TS) muscles. Our data indicate that similar to 46% of the medial gastrocnemius (MG) muscle was activated during the exercise, with activation of the lateral gastrocnemius (LG) and soleus (Sol) muscles being similar to 35%. In the MG, distal portions had a greater percentage area of activated muscle than the proximal portions (P &lt; 0.05), which was consistent with the results regarding electromyogram, activity. In contrast, regional activation differences were not observed in the LG and Sol. These findings suggest that the amounts of activated muscle and its distribution would be different among TS muscles.

This paper describes the modeling and simulation of the deformation of human skeletal muscle at different structural levels based on sound scientific principles, experimental evidence, and state-of-art muscle anatomy and physiology. The equations of a continuum model of a muscle with realistic architecture, including internal arrangement Of muscle fibers and passive structures, and deformation, including activation relations, was developed and solved with the finite element method. The continuum model is used as the basis of a strategy for controlling muscle deformation using activation relations. In order to demonstrate the functionality of the model, it was used to investigate force production and structural changes during contraction of the human tibialis anterior for maximally and submaximally activated muscle behavior. From a comparison with experimental data obtained from ultrasound imaging, we concluded that the modeling and simulation of the continuum based on physiologically meaningful parameters as described in the paper is both an excellent predictor of force production observations and of changes in internal geometry under various test conditions. It is therefore a valuable tool for controlling muscle deformation during movement. Copyright (c) 2005 John Wiley & Sons, Ltd.

Real-time ultrasonography enabled in vivo MTC scanning and promised a realistic determination of the interactions between muscle and tendon during human movements. The tendinous tissues were quite compliant, and the elastic property was different among muscles. Internal shortening of fascicle was caused by the tendon elasticity. During human movements such as jumping, walking and ankle extension-flexion exercise the muscle fiber contracted with nearly constant length, while the tendon performed stretch-shortening cycle. It is suggested that human MTC are designed to match muscle force generation and tendon elasticity for efficient movement performance.

This study aimed to investigate the accuracy of estimating the volume of limb muscles (MV) using ultrasonographic muscle thickness (MT) measurements. The MT and MV of each of elbow flexors and extensors, knee extensors and ankle plantar flexors were determined from a single ultrasonographic image and multiple magnetic resonance imaging (MRI) scans, respectively, in 27 healthy men (23-40 years of age) who were allocated to validation (n=14) and cross-validation groups (n=13). In the validation group, simple and multiple regression equations using MT and a set of MT and limb length, respectively, as independent variables were derived to estimate the MV measured by MRI. However, only the multiple regression equations were cross-validated, and so the prediction equations with r(2) of 0.787-0.884 and the standard error of estimate of 22.1 cm(3) (7.3%) for the elbow flexors to 198.5 cm(3) (11.1%) for the knee extensors were developed using the pooled data. This approach did not induce significant systematic error in any muscle group, with no significant difference in the accuracy of estimating MV between muscle groups. In the multiple regression equations, the relative contribution of MT for predicting MV varied from 41.9% for the knee extensors to 70.4% for the elbow flexors. Thus, ultrasonographic MT measurement was a good predictor of MV when combined with limb length. For predicting MV, however, the unsuitability of a simple equation using MT only and the difference between muscle groups in the relative contribution of MT in multiple regression equations indicated a need for further research on the limb site selected and muscle analyzed for MT measurement.

Seven high school boys (16.4 +/- 0.5y, mean +/- SD) and 7 girls (16.4 +/- 0.5y), who specialized in track and field events, performed ten 5-s maximal sprint runs with an interval of 10s between each sprint on a non-motorized running ergometer. In each sprint, the mean mechanical power (MP) from the start until the belt velocity of the ergometer (i.e., running velocity) peaked was calculated. The boys showed significantly higher MP than the girls in all sprints. However, when MP was expressed as the ratio to the total volume of muscles located in the right lower limb (MP x MV-1), estimated using a bioelectrical impedance analysis, significant gender effect was limited to the values at the 1(st) and 2(nd) sprints. The decline of MP over the ten sprints, expressed as a relative value to that at the 1(st) sprint, was greater in boys (46.2 +/- 7.6%) than in girls (33.9 +/- 8.6%), and significantly correlated with MP x MV-1 at the 1(st) sprint (r = 0.568, p &lt; 0.05). However, no significant difference between the boys and girls Was found in the relative difference between NIP values at the 3(rd) and 10(th) sprints, where the gender difference in MP x MV-1 at every sprint was insignificant. The findings here indicate that, for trained teenage boys and girls, 1) significant gender difference in mechanical power developed during repeated bouts of maximal running exists only in the initial phase of the task, when the difference in the volume of the lower limb muscles is normalized, and 2) it may be a reason for a greater decline of mechanical power developed during the bout in boys compared to girls.

Purpose: A 20-d 6degrees head-down tilt bed rest project was conducted to evaluate the effect of dynamic leg press and plantar flexion resistance training on muscle size and function in human plantar flexors (PF) throughout the prolonged bed rest. Methods: Twelve healthy men participated in this study and were divided two groups: resistance training (BR-Tr group: N=6, age: 23+/-2 yr, height: 170+/-3 cm, weight: 66+/-7 kg) and nontraining (BR-Cont group: N=6, age: 23+/-1 yr, height: 170+/-3 cm, weight: 67+/-6 kg) during the bed rest. Physiological cross-sectional area (PCSA) and peak torque of the PF muscle group was determined. Spin-spin relaxation times (T2) of the medial (MG) and lateral gastrocnemius (LG) and soleus (Sol) muscle was measured at rest and immediately after unilateral calf-raising exercise (5 sets of 10 reps). Results: PCSA of the PF muscle group did not show any significant change in BR-Tr group; however, for the BR-Cont group, PCSA decreased by 13% after bed rest (P&lt;0.05). There was no significant change in exercise-induced T2 change of the MG, LG, or Sol muscles between before and after the bed rest in BR-Tr group; however, in the BR-Cont group, significant increases in T2 were found in these three muscles after the bed rest (P&lt;0.05 to 0.01). Conclusion: We conclude that dynamic leg press and plantar flexion resistance training during bed rest maintains muscle size and function (torque and T2), and that this training could be useful for prevention of progressive muscle deconditioning during spaceflight.

The thickness, fascicle angles of pennation, and fascicle length of the vastus lateralis (VL) and medial gastrocnemius (MG) muscles in highly trained soccer players and swimmers of both genders were determined from ulrasonograms to investigate whether the fascicle arrangements of the lower limb muscles in the athletes could be related to the requirements of the events, i.e., intensive muscular activities in the water versus on the ground. In comparisons between the two events, the soccer players tended to show shorter fascicles and greater fascicle angles, and the swimmers thicker muscles and longer fascicles, especially in VL. In both events, the males showed thicker muscles and greater fascicle angles than the females. In both VL and MG, the thickness, fascicle length and fascicle angle were related to each other in a right-angled triangle model, and so, most of the event-and/or gender-related differences observed in the fascicle angle depended on the difference in muscle thickness relative to fascicle length. The present data cannot answer the question of whether the athletes had muscles suited to their respective sports prior to beginning their sports or whether the muscles adapted specifically to the competitive and/or training styles. However, it might be assumed that the lower limb muscles for swimmers are suitable to perform rapid, powerful kick movements during competitive swims by having greater thickness and longer fascicle, i.e., priorities in both force production and shortening velocity, but those for soccer players do not show architectural profiles which can be related to intensive activity on the ground, except that the thickness values exceed the normal range.

The influence of muscle series elasticity on the relationship between torque and joint angle during dynamic contractions was studied. The torque-angle relationship during the maximal isokinetic knee extension was determined for six male subjects (25-45 years) at 0.52, 1.05, 1.57, 2.09, 2.62, 3.49 rad/s. The knee joint angle at which peak torque was observed showed a systematic shift to more extended positions, i.e., the quadriceps muscle-tendon unit length became shorter as the velocity increased [from 1.01 (0.12) rad (0.52 rad/s) to 0.75 (0.14) rad (3.49 rad/s), mean (SD)]. The corresponding difference in muscle-tendon unit length between 0.52 and 3.49 rad/s, estimated from the angle shift at peak torque and the moment arm length change of the quadriceps muscles, was 9 (4) mm. The relationship between estimated changes in muscle-tendon unit length and muscle force of the vastus lateralis and intermedius (VLI) over the seven velocities (including isometric contraction, 0 rad/s) coincided with the load-elongation properties of the series elastic component of VLI, determined separately in vivo by ultrasonography when the same subjects performed a ramp isometric knee extension. The results suggest that the torque-angle relationship is affected by the interaction between contractile and elastic components, and that peak torque angle shift is attributable to the elongation of tendinous tissues as a function of force applied to them.

Muscle and tendon interaction was estimated in vivo by real-time ultrasonography. Differences between muscles in internal muscle-fiber shortening during isometric actions are due to the elastic properties of tendon. Compliant human tendons allow muscles to contract isometrically during many human movements for efficient force generation.

Isometric unilateral elbow extension training was conducted for 10 weeks (3 times per week) on 12 young adult men to investigate the effects of equivolume exercise programs with different combinations of intensity and duration on the morphological and functional aspects of the triceps brachii muscle. One group of 6 subjects trained by developing maximal voluntary contraction (MVC) for 6 s per set with, 12 sets per session (100%G), while the other group of 15 subjects trained at 60% of MVC for 30 s per set with 4 sets per session (60%G). Training significantly increased the muscle volume (V-m), fascicle pennation angle of the triceps brachii, and torque output during concentric and eccentric elbow extensions at three constant velocities of 0.52, 1.57, and 3.14 rad.s(-1) as well as under the training condition, with no significant differences in the relative gains between the two programs. However, 100%G showed significantly greater V-m than 60%G after training, when V-m before training was normalized. Thus, only 60%G significantly increased the ratio of torque to V-m developed in the eccentric actions at the three velocities and concentric action at 1.57 rad.s(-1). The present results indicate that isometric training programs of medium resistance/long duration and high resistance/short duration produce different effects on V-m, and dynamic strength relative to V-m even if the training volume is equalized between the two protocols.

Six men performed a single ankle plantar flexion exercise in the supine position with the maximal effort with counter movement (CM, plantar flexion preceded by dorsiflexion) and without counter movement (NoCM, plantar flexion only) produced by a sliding table that controlled applied load to the ankle (40% of the maximal voluntary force). The reaction force at the foot and ankle joint angle were measured using a force plate and a goniometer, respectively. From real-time ultrasonography of the gastrocnemius medialis muscle during the movement, the fascicle length was determined. The estimated peakforce, average power, and work at the Achilles' tendon during the plantar flexion phase in CM were significantly greater than those in NoCM. In CM, in the dorsiflexion phase, fascicle length initially increased with little electromyographic activity, then remained constant while the whole muscle-tendon unit lengthened, before decreasing in the final plantar flexion phase. In NoCM, fascicle length decreased throughout the movement and the fascicle length at the onset of movement was longer than that of the corresponding phase in CM. It was concluded that during CM muscle fibres optimally work almost isometrically, by leaving the task of storing and releasing elastic energy for enhancing exercise performance to the tendon.

Two questions were addressed in this study: (1) how much strain of the superficial aponeurosis of the human medial gastrocnemius muscle (MG) was obtained during voluntary isometric contractions in vivo, (2) whether there existed inhomogeneity of the strain along the superficial aponeurosis. Seven male subjects, whose knees were extended and ankles were flexed at right angle, performed isometric plantar flexion while elongation of superficial aponeurosis of MG was determined from the movements of the intersections made by the superficial aponeurosis and fascicles using ultrasonography. The strain of the superficial aponeurosis at the maximum voluntary contraction, estimated from the elongation and length data, was 5.6 +/- 1.2%. There was no significant difference in strain between the proximal and distal parts of the superficial aponeurosis. Based on the present result and that of our previous study for the same subjects (J. Appl. Physiol 90 (2001) 1671), a model was formulated for a contracting uni-pennate muscle-tendon unit. This model, which could be applied to isometric contractions at other angles and therefore of wide use, showed that similar strain between superficial and deep aponeuroses of MG contributed to homogeneous fascicle length change within MG during contractions. These findings would contribute to clarifying the functions of the superficial aponeurosis and the effects of the superficial aponeurosis elongation on the whole muscle behavior. (C) 2002 Elsevier Science Ltd. All rights reserved.

The purpose of this study was to investigate the viscoelastic properties of tendon structures in humans. Elongation of the tendon and aponeurosis of medial gastrocnemius muscle (MG) was directly measured by ultrasonography, while subjects (n=19) performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between tendon elongation (L) and estimated muscle force (Fm) was fitted to a linear regression, the slope of which was defined as compliance of the tendon structures. The hysteresis was calculated as the ratio of the area within the L-Fm loop (elastic energy dissipated) to the area beneath the load portion of the curve (elastic energy input). The resulting L-Fm relationship was non-linear in form, as previously reported on animal and human tendons in vitro. The mean compliance was 4.5+/-1.1 . 10(-2) mm/N. However, there was a considerable inter-subject variability (2.9 to 7.2 . 10(-2) mm/N). The Young's modulus, i.e., the slope of the stress-strain curve, was 280 MPa, which tended to be lower than the previously reported values for human tendons. It was also found that the strain of the tendon structures was homogeneously distributed along their length. The mean hysteresis (energy dissipation) was 22.2+/-8.8%. However, again there was a considerable inter-subject variability (9.7 to 37.2%). The present results indicated that the tendon structures of human MG were considerably compliant and their hysteresis was in accordance with previously reported values.

The extent of elongation and slackness of aponeurosis and tendon, and muscle fiber length of human medial gastrocnemius muscle are determined in vivo using ultrasonography. The ankle joint is passively moved at 50/s within the joint range of -36 to 7degrees (0degrees = neutral anatomic position; positive values for dorsiflexion) by a dynamometer while the length change of the aponeurosis and tendon is determined using ultrasonography (n = 8 men), Strain is calculated as the length change relative to the reference length of aponeurosis and tendon when the passive joint moment is 0. Elongation (positive strain Accepted after revision: February 10, 2002 values) of aponeurosis and tendon at 7degrees are 2.1 +/- 1.1 and 2.4 +/- 1.0%, respectively. The extent of slackness (negative strain values) of aponeurosis and tendon at -36degrees are -1.8 +/- 1.1 and -3.5 +/- 1.6%, respectively, and there is a significant difference between them (p &lt; 0.05). This may be related to the existence of muscle fibers that attach to the aponeurosis over its whole length and do not allow it to fold. The results indicate that the length change of aponeurosis and tendon of medial gastrocnemius muscle occurs over the range of ankle joint positions even during passive joint motions. Copyright (C) 2002 S. Karger AG, Basel.

Fascicle curvature of human medial gastrocnemius muscle (MG) was determined in vivo by ultrasonography during isometric contractions at three (distal, central, and proximal) locations (n=7) and at three ankle angles (n=7). The curvature significantly (P&lt;0.05) increased from rest to maximum voluntary contraction (MVC) (0.4-5.2 m(-1)). In addition, the curvature at MVC became larger in the order dorsiflexed, neutral, plantar flexed (P&lt;0.05). Thus both contraction levels and muscle length affected the curvature. Intramuscular differences in neither the curvature nor the fascicle length were found. The direction of curving was consistent along the muscle: fascicles were concave in the proximal side. Fascicle length estimated from the pennation angle and muscle thickness, under the assumption that the fascicle was straight, was underestimated by similar to6%. In addition, the curvature was significantly correlated to pennation angle and muscle thickness. These findings are particularly important for understanding the mechanical functions of human skeletal muscle in vivo.

The interaction between contractile force and in-series compliance was investigated for the intact skeletal muscle-tendon unit (MTU) of Rana pipiens semitendinosus muscles during fixed-end contraction. It was hypothesized that internal sarcomere shortening is a function of the length-force characteristics of contractile and series elastic components. The MTUs (n = 18) were dissected, and, while submerged in Ringer's solution, muscles were activated at nine muscle lengths(-2 to +6 mm relative to optimal length in 1 mm intervals), while measuring muscle force and sarcomere length (SL) by laser diffraction. The MTU was clamped either at the bone (n = 6), or at the proximal and distal ends of the aponeuroses (n = 6). Muscle fibers were also trimmed along with aponeuroses down to 5-20 fibers and identical measurements were performed (n = 6). The magnitude of shortening decreased as MTU length increased. The magnitude of shortening ranged from -0.08 to 0.3 mu m, and there was no significant difference between Delta SL as a function of clamp location. When aponeuroses were trimmed, sarcomere shortening was not observed at L-0 and longer. These results suggest that the aponeurosis is the major contributor to in-series compliance. Results also support our hypothesis but there also appear to be other factors affecting internal sarcomere shortening. The functional consequence of internal sarcomere shortening as a function of sarcomere length was to skew the muscle length-tension relationship to longer sarcomere lengths. (C) 2000 Elsevier Science Ltd. All rights reserved.

Nine healthy men (22-45 yr) completed 100 repetitive maximal isometric contractions of the ankle plantar flexor muscles in two knee positions of full extension (K0) and flexion at 90 degrees (K90), positions that varied the contribution of the gastrocnemii. Electromyographic activity was recorded from the medial and lateral gastrocnemii and soleus muscles by using surface electrodes. Plantar flexion torque in K0 was greater and decreased more rapidly than in K90. The electromyographic amplitude decreased over time, and there were no significant differences between muscles and knee joint positions. The level of voluntary effort, assessed by a supramaximal electrical stimulation during every 10th contraction, decreased from 96 to 70% (P &lt; 0.05) with no difference between K0 and K90. It was suggested that a decrease in plantar flexion torque was attributable to both central and peripheral fatigue and that greater fatigability in K0 than in K90 would result from a greater contribution and hence more pronounced fatigue of the gastrocnemius muscle. Further support for this possibility was provided from changes in twitch torque.

This paper reviews three of our recent studies on human muscle architecture in vivo. 1. Hypertrophic changes: From B-mode ultrasonograms, pennation angles and thickness of triceps brachii were determined for normal subjects and highly-trained bodybuilders. There was a significant correlation between muscle thickness and pennation angles. It was confirmed that hypertrophy was accompanied by an increase in pennation angles. 2. Variation of fascicle architecture: Fascicle lengths and pennation angles were obtained from different positions in the gastrocnemius muscle while the subjects relaxed and performed isometric planter flexion. The fascicle length was uniform throughout the muscle and shortened by contraction (30-34% at 50% of the maximal force). On the other hand, pennation angles differed among positions and increased by contraction. The muscle thickness did not change by contraction. Pennation angles were significantly correlated with muscle thickness within muscle. 3. Joint position-fascicle length relationships: Ultrasonic images of the gastrocnemius and soleus muscles were obtained while the subject performed maximal isometric plantarflexion at various joint positions, from which fascicle lengths and angles were determined. The length-force relationship of each muscle was estimated. It was suggested that human muscle architecture has an ability to make substantial changes to adapt to environmental conditions.

Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15 degrees dorsiflexion (-15 degrees) and 0, 15, and 30 degrees plantar flexion, with the knee set at 0, 45, and 90 degrees. At each position, longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (Sol) muscles were obtained while the subject was relaxed (passive) and performed maximal isometric plantar flexion (active), from which fascicle lengths and angles with respect to the aponeuroses were determined. In the passive condition, fascicle lengths changed from 59, 65, and 43 mm (knee, 0 degrees; ankle, -15 degrees) to 32, 41, and 30 mm (knee, 90 degrees ankle, 30 degrees) for MG, LG, and Sol, respectively. Fascicle shortening by contraction was more pronounced at longer fascicle lengths. MG had greatest fascicle angles, ranging from 22 to 67 degrees, and was in a very disadvantageous condition when the knee was flexed at 90 degrees, irrespective of ankle positions. Different lengths and angles of fascicles, and their changes by contraction, might be related to differences in force-producing capabilities of the muscles and elastic characteristics of tendons and aponeuroses.

Six male subjects made maximal isometric plantar flexions unilaterally (UL and bilaterally (BL. with the knee joint angle positioned at 90 degrees and 0 degrees (full extension) and the ankle joint kept at 90 degrees. Plantar flexion torque and electromyogram (EMG) of the lateral gastrocnemius (LG) and the soleus (Sol) muscles were recorded. There was a deficit in torque in BL compared to UL (P &lt; 0.05), and the deficit was greater when the knee was extended than when bent to 90 degrees (13.9% vs 6.6%). The integrated EMG (IEMG) of UL and BL did not differ when the knee was at 90 degrees. On the other hand, when the knee was extended IEMG of LG was smaller for BL than for UL, suggesting that the larger bilateral deficit when the knee was extended was due to a reduced activity of the LG motor units. In addition, the H-reflex recorded from Sol when the contralateral leg was performing a maximal unilateral plantarflexion was reduced. This would indicate that the force deficit was associated with a reduction of motoneuron excitability.

We have developed a technique to determine fascicle length in human vastus lateralis muscle in vivo by using ultrasonography. When the subjects had the knee fully extended passively from a position of 110 degrees flexion (relaxed condition), the fascicle length decreased from 133 to 97 mm on average. During static contractions at 10% of maximal voluntary contraction strength (tensed condition), fascicle shortening was more pronounced (from 126 to 67 mm), especially when the knee was closer to full extension. Similarly as the knee was extended, the angle of pennation (fascicle angle, defined as the angle between fascicles and aponeurosis) increased (relaxed, from 14 to 18 degrees; tensed, from 14 to 21 degrees), and a greater increase in the pennation angle was observed in the tensed than in the relaxed condition when the knee was close to extension (&lt;40 degrees). We conclude that there are differences in fascicle lengths and pennation angles when the muscle is in a relaxed and isometrically tensed conditions and that the differences are affected by joint angles, at least at the submaximal contraction level.

Five men underwent unilateral resistance training of elbow extensor (triceps brachii) muscles for 16 weeks. Before and after training, muscle layer thickness and fascicle angles of the long head of the triceps muscle were measured in vivo using B-mode ultrasound, and fascicle lengths were estimated. Series anatomical cross-sectional areas (ACSA) of the triceps brachii muscle were measured by magnetic resonance imaging, from which muscle volume (V-m) was determined and physiological cross-sectional area (PCSA) was calculated. Elbow extension strength (isometric; concentric and eccentric at 30, 90 and 180 degrees . s(-1)) was measured using an isokinetic dynamometer to determine specific tension. Muscle volumes, ACSA, PCSA, muscle layer thickness and fascicle angles increased after training and their relative changes were similar, while muscle and fascicle length did not change. Muscle strength increased at all velocities; however, specific tension decreased after training. Increase in fascicle angles, which would be the result of increased V-m and PCSA, would seem to imply the occurrence of changes in muscle architecture. This might have given a negative effect on the force-generating properties of the muscles.

Series cross-section images of the upper extremity were obtained for four men by magnetic resonance imaging (MRI) and anatomical cross-sectional areas (ACSA) of elbow flexor muscles [biceps brachii (BIC), brachialis (BRA), brachioradialis (BRD)] and extensor muscles [triceps brachii (TRI)] were measured. Physiological cross-sectional area (PCSA) was calculated from the muscle volume and muscle fibre length, the former from the series ACSA and the latter from the muscle length multiplied by previously reported fibre/muscle length ratios. Elbow flexion/extension torque was measured using an isokinetic dynamometer and the force at the tendons was calculated from the torque and moment arms of muscles measured by MRI. Maximal ACSA of TRI was comparable to that of total flexors, while PCSA of TRI was greater by 1.9 times. Within flexors, BRA had the greatest contribution to torque (47%), followed; by BIC (34%) and BRD (19%). Specific tension related to the estimated velocity of muscle fibres were similar for elbow flexors and extensors, suggesting that the capacity of tension development is analogous between two muscle groups.

A total of 117 Japanese subjects (62 men and 55 women) volunteered for the study. Subcutaneous adipose tissue (AT) and muscle thicknesses were measured by B-mode ultrasonography at nine sites of the body. Body density (BD) was determined the hydrodensitometry. Reproducibility of thickness measurements by ultrasonography was high (r = 0.96-0.99). Correlations between AT thickness and BD ranged from -0.46 (gastrocnemius) to -0.87 (abdomen) for males and -0.46 (gastrocnemius) to -0.84 (abdomen) for females. A higher negative correlation (r = -0.89) was observed for the sum of AT thicknesses (forearm, biceps, triceps, abdomen, subscapula, quadriceps, hamstrings, gastrocnemius, and tibialis anterior) both in males and in females. Slightly lower coefficients were observed between muscle thickness and LBM (r = 0.36 to r = 0.70 for males and r = 0.44 to r = 0.55 for females). Prediction equations for BD and LBM from AT and muscle thickness were obtained by multiple regression analysis. Cross-validation on a separate sample (33 men and 44 women) showed an accurate prediction for BD. The present findings suggest that B-mode ultrasonography can be applied in clinical assessment and field surveys. © 1994 Wiley-Liss, Inc.

If limitations exist in skeletal dimensions, fat-free mass (FFM) might have an upper limit. To explore the upper limit to FFM, 37 professional Japanese Sumo wrestlers, 14 highly trained bodybuilders, and 26 untrained men were investigated for body composition (fat mass and FFM) and cross-sectional areas (CSA) of limb muscles, by hydrodensitometry and ultrasound, respectively. Mean % fat of Sumo wrestlers, bodybuilders, and untrained subjects were, respectively, 26.1%, 10.9%, and 12.1%. Sumo wrestlers had a significantly greater FFM than bodybuilders, who had a greater FFM than the untrained men. Six of the wrestlers had more than 100 kg of FFM, including the largest one of 121.3 kg (stature: 186 cm, mass: 181 kg, %fat: 33.0%). The FFM/stature ratio of elite Sumo wrestlers averaged at 0.61 kg/cm, with the highest 0.66 kg/cm. It is suggested that a FFM/stature ratio of 0.7 kg/cm may be an upper limit in humans. © 1994 Wiley-Liss, Inc.

The purpose of this study was to investigate the force-producing characteristics of boys aged 13 years in relation to fatigue of elbow flexor muscles. Maximal voluntary force in elbow flexion was measured before and after a muscle endurance test (MET) by using an isokinetic dynamometer isometrically, concentrically and eccentrically at three velocities, i.e. 0.21, 0.52, and 1.05 rad - s-1. The MET consisted of maximal concentric and eccentric muscle actions performed alternately at 0.52 rad - s-1 for 50 consecutive trials. Muscle cross-sectional area (CSA) of elbow flexor muscles (biceps brachii and brachialis) was measured by a B-mode ultrasound apparatus. Although eccentric force showed significantly higher values than concentric force during MET, there was no significant difference in the rate of decline in force between the two actions. There was no significant difference in the rate of decline in force after MET for each velocity and muscle action. Isometric, concentric and eccentric force before MET was significantly related to muscle CSA whereas, after MET, concentric force significantly correlated with muscle CSA but there was no significant correlation between muscle CSA and isometric or eccentric force. From our study, it is therefore suggested that in development to maturity, isometric, concentric and eccentric force decrease at the same rate with advancing muscle fatigue; however, there might be differences among muscle actions in facors affecting force development.

Muscle-fiber pennation angles were measured in vivo with the use of ultrasonography to investigate the relationship between fiber pennation and muscle size for 32 male subjects (from untrained subjects to highly trained bodybuilders). From the image of a B-mode ultrasonogram, fiber pennation angles and thickness of triceps brachii were determined, the former as angles between echoes from the interspaces of fascicles and from the aponeurosis of long and medial heads of triceps and the latter as the distance between the fat-muscle and muscle-bone interfaces. The pennation angles were in the range of 15 and 53-degrees for the long head and 9 to 26-degrees for the medial head, which were similar to or greater than the published and the present data on human cadavers. Significant differences were observed between normal subjects and bodybuilders in muscle thickness and pennation angles (P &lt; 0.01), and there were significant correlations between muscle thickness and pennation angles for both long (r = 0.884) and medial (r = 0.833) heads of triceps, suggesting that muscle hypertrophy involves an increase in fiber pennation angles.

Ten healthy male subjects carried out bilateral concentric leg extension training twice a week for 8 weeks. Before and after the training, maximal voluntary isometric and isokinetic strength and cross‐sectional areas of the quadriceps femoris were measured. Maximal bilateral leg extension power increased significantly after the training. Isometric and concentric unilateral strength did not change significantly before and after the training, while eccentric strength at 0.52 and 1.05 rad·s−1 increased after the training with no changes in cross‐sectional area. The correlations between strength and cross‐sectional area increased significantly after the training. It was speculated that the increase in eccentric strength of knee extensors was due to modification of the neural inhibition during eccentric muscle actions. Copyright © 1993, Wiley Blackwell. All rights reserved

The purpose of the present study was to check the reliability of measurements of oxygen uptake (VO2) using a newly developed portable telemetry system. This system (K2) consisted of a face mask, a flow meter, a gas analyser with a transmitter, and a receiver. The total mass for the subject to carry was about 850 g. Three experiments were carried out, firstly to check the reliability and reproducibility of the flow meter and the K2 gas analyser, secondly to check the accuracy of K2 by comparing it with the Douglas bag method (DB), and thirdly to apply K2 to sports activities. In the first experiment, the flow meter was highly accurate up to 180 1 . min -1 with good reproducibility. The measurement error of the gas analyser was less than 2%. In the second experiment, there was no significant difference in the calculated ventilation between K2 and DB. The VO2 showed no significant difference between K2 and DB with some exceptions. In the third experiment, we succeeded in the measurement of VO2 during rowing on water. The measurement of VO2 during running and playing soccer was also possible. It would seem that the present system could well be a powerful tool in the field measurement of VO2 during various sports activities.