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 < 0.05). The % activated volumes with a high level of activation were larger in the medial gastrocnemius than the soleus (Sol; P < 0.05). The Sol had a larger % activated volume with a low level of activation than the lateral gastrocnemius (P < 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.

Purpose: This study aimed to investigate how the cross-sectional areas (CSA) of the quadriceps femoris (QF)3, hamstrings (Ham), and psoas major (PM) in junior sprinters are related to mean running velocity (MV100m) calculated from official records of 100-m races. Methods: In 44 sprinters (22 boys and 22 girls) aged 14-17 yr, cross-sectional images were taken at the upper thigh and midthigh and midway between the fourth and fifth lumbar vertebrae using magnetic resonance imaging. CSA of the three muscles located in both sides were analyzed. For each muscle, the mean values of the CSA of the right and left sides were calculated and used for regression analyses of the relationships between CSA variables and MV100m. Results: Stepwise multiple-regression analyses produced prediction equations of MV100m with independent variables of QF CSA at the midthigh and PM-to-QF CSA ratio at the upper thigh for boys (R-2 = 0.38) and PM-to-QF CSA ratio at the midthigh for girls (R-2 = 0.33). In the regression model for boys, QF CSA at the midthigh had a negative regression coefficient. Conclusion: For junior sprinters of both genders, the higher development of PM relative to QF, rather than absolute muscle size, is a factor in achieving a better performance in 100-m race performance.

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.

In animal models, several ubiquitin ligases play an important role in skeletal muscle atrophy caused by unloading. In this study we examined protein ubiquitination and ubiquitin ligase gene expression in quadriceps femoris muscle from healthy volunteers after 20-day bedrest to clarify ubiquitin-dependent proteolysis in human muscles after unloading. During bedrest, thickness and cross-sectional area of the quadriceps femoris muscle decreased significantly by 4.6% and 3.7%, respectively. Ubiquitinated proteins accumulated in these atrophied human muscles. A real-time reverse transcription-polymerase chain reaction system showed that bedrest significantly upregulated expression of two ubiquitin ligase genes, Cbl-b and atrogin-1. We also performed DNA microarray analysis to examine comprehensive gene expression in the atrophied muscle. Bedrest mainly suppressed the expression of muscle genes associated with control of gene expression in skeletal muscle. Our results suggest that, in humans, Cbl-b-or atrogin-1-mediated ubiquitination plays an important role in unloading-induced muscle atrophy, and that unloading stress may preferentially inhibit transcriptional responses in skeletal muscle.

Background. Subacromial impingement is a widely recognized mechanism of chronic shoulder pain. The magnitudes of the compressive forces that impinge the subacromial structures were often measured from cadaveric specimens, but it is questionable to use this data as a sole basis to determine the shoulder motions and/or shoulder configurations that induce impingement in live subjects performing active motion. The purpose of the present study was to determine in vivo the magnitude of the compressive force at selected shoulder configurations.
Methods. The subacromial structures may be impinged by the downward-directed forces exerted by the coraco-acromial ligament. The reactions of these forces push the ligament upwards and deform it into a curved shape. A single resultant of these reaction forces was determined with an inverse approach to quantify the magnitude of the impingement force. An ultrasound unit was used to visualize the deformed shape of the coraco-acromial ligament for thirteen subjects with no symptomatic shoulder problem actively holding their shoulders in five configurations.
Findings. The impingement force in 90 degrees abduction + maximum internal rotation (mean = 21.3 N) and that in the Hawkins test position (mean = 18.3 N) were significantly greater than those in 90' abduction + neutral and external rotation (means <= 3 N).
Interpretation. For young asympt6matic shoulders, the motions that induce impingement are not any arm abduction, but the arm abduction with a large internal rotation. Further study is indicated to examine the impingement force among various age groups. (c) 2006 Elsevier Ltd. All rights reserved.

The purpose of this study was to investigate the influences of isometric training at different joint angles on the muscle size and function of the human muscle-tendon complex in vivo. Furthermore, we tried to gain a better understanding of the mechanisms involved in angle specificity after isometric training from the aspect of neuromuscular adaptation and the changes in the properties of the muscle-tendon complex. Nine males completed 12-week unilateral training program (70% of maximal voluntary contraction (MVC) x 15s x six sets) on the knee extensors at 50 degrees (shorter muscle length: ST) and 100 degrees (longer muscle length: LT). The internal muscle force (mechanical stress) is higher at 100 degrees than at 50 degrees because of the difference in the moment arm length, although there were no difference in the relative torque level, contraction and relaxation times, and repetition between ST and LT. Before and after training, isometric strength at eight angles and muscle volume were determined. Tendon elongation of knee extensors was measured by ultrasonography. There was no significant difference in the rate of increment of muscle volume between the protocols. Tendon stiffness increased significantly for LT, but not for ST. Although significant gain was limited to angles at or near the training angle for ST, increases in MVC at all angles were found for LT. These results suggest that only mechanical stress (internal muscle force imposed on muscle and tendon) contributes to adaptation in the tendon stiffness, although metabolic (relative torque level, etc.) and mechanical stress relate to muscle hypertrophy. Furthermore, increment of tendon stiffness for LT might contribute to increase torque output at smaller angles other than the training angle.

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<.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<.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.

The present study aimed to investigate the effects of low-load resistance training with vascular occlusion on the specific tension and tendon properties by comparing with those of high-load training. Nine participants completed 12 weeks (3 days/week) of a unilateral isotonic training program on knee extensors. One leg was trained using low load (20% of 1 RM) with vascular occlusion (LLO) and other leg using high load (80% of 1 RM) without vascular occlusion (HL). Before and after training, maximal isometric knee extension torque (MVC) and muscle volume were measured. Specific tension of vastus lateralis muscle (VL) was calculated from MVC, muscle volume, and muscle architecture measurements. Stiffness of tendon-aponeurosis complex in VL was measured using ultrasonography during isometric knee extension. Both protocols significantly increased MVC and muscle volume of quadriceps femoris muscle. Specific tension of VL increased significantly 5.5% for HL, but not for LLO. The LLO protocol did not alter the stiffness of tendon-aponeurosis complex in knee extensors, while the HL protocol increased it significantly. The present study demonstrated that the specific tension and tendon properties were found to remain following low-load resistance training with vascular occlusion, whereas they increased significantly after high-load training.

Growth trends in the cross-sectional area of the quadriceps femoris (CSA(QF)) and its dynamic strength in 12 teenage tennis players (six boys and six girls), aged from 10.7 to 13.2 years at the onset of the study, were investigated through a 2-year follow-up survey. CSA(QF) values at the three levels (proximal, mid, and distal to the knee joint) and dynamic torques during knee extensions at three pre-set velocities (1.05, 3.14, and 5.24 rad/s) were determined year by year, i.e., three times (T1, T2, and T3), using magnetic resonance imaging and an isokinetic dynamometer, respectively. In both genders, the CSA(QF) values at the three levels tended to increase across the measurement times, with greater gains in the boys than in the girls at the levels mid and distal to the knee joint. Among these changes, only the CSA(QF) at the level proximal to the knee joint significantly increased regardless of changes in both skeletal age and body height. The ratios of torque to the sum of CSA(QF) at the three levels (T/CSA) at 3.14 and 5.24 rad/s for the boys and at 5.24 rad/s for the girls were significantly higher in T2 and T3 than T1. Further, the relative increases in torque and T/CSA values at 3.14 and 5.24 rad/s were greater in the boys than the girls. The findings presented here indicate that young tennis players who are in the earlier stage of adolescence increase the CSA of the QF muscle beyond normally expected growth change at the level proximal to the knee joint and show a predominant development in torque generation capability during high-velocity knee extensions, with a greater gain in boys compared with girls.

Force fluctuations during steady contractions of multiple agonist muscles may be influenced by the relative contribution of force by each muscle. The purpose of the study was to compare force fluctuations during steady contractions performed with the plantar flexor muscles in different knee positions. Nine men (25.8 +/- 5.1 years) performed steady contractions of the plantar flexor muscles in the knee-flexed and knee-extended (greater involvement of the gastrocnemii muscles) positions. The maximal voluntary contraction (MVC) force was 32% greater in the knee-extended position compared with the knee-flexed position. The target forces were 2.5-10% MVC force in the respective position. The amplitude of electromyogram in the medial gastrocnemius muscle was greater in the knee-extended position (10.50 +/- 9.80%) compared with the knee-flexed position (1.26 +/- 1.15%, P < 0.01). The amplitude of electromyogram in the soleus muscle was not influenced by the knee position. The amplitude of electromyogram in the lateral gastrocnemius and tibialis anterior muscles was marginal and unaltered with knee position. At the same force (in Newtons), the standard deviation of force was lower in the knee-extended position compared with the knee-flexed position. These results indicate that force fluctuations during plantar flexion are attenuated with greater involvement of the medial gastrocnemius muscle.

The present study aimed to investigate the effect of isometric squat training on human tendon stiffness and jump performances. Eight subjects completed 12 weeks (4 days/week) of isometric squat training, which consisted of bilateral leg extension at 70% of maximum voluntary contraction (MVC) for 15 s per set (10 sets/day). Before and after training, the elongations of the tendon-aponeurosis complex in the vastus lateralis muscle and patella tendon were directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation was fitted to a linear regression, the slope of which was defined as stiffness. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The training significantly increased the volume (P < 0.01) and MVC torque (P < 0.01) of the quadriceps femoris muscle. The stiffness of the tendon-aponeurosis complex increased significantly from 51 +/- 22 (mean +/- SD) to 59 +/- 24 N/mm (P=0.04), although that of the patella tendon did not change (P=0.48). The SJ height increased significantly after training (P=0.03), although the CMJ height did not (P=0.45). In addition, the relative difference in jump height between SJ and CMJ decreased significantly after training (P=0.02). These results suggest that isometric squat training changes the stiffness of human tendon-aponeurosis complex in knee extensors to act negatively on the effects of pre-stretch during stretch-shortening cycle exercises.

This study aimed to investigate the validity of using segmental bioelectrical impedance (BI) analysis for estimating skeletal muscle volume (MV) in the trunk, defined as the body segment from the acromion process to the greater trochanter. Using a magnetic resonance imaging (MRI) method, the trunk MV was determined in 28 men (19 similar to 34 yr), divided into validation (n similar to 20) and cross-validation (n similar to 8) groups, and used as a reference (MVMRI). For BI measurements of the trunk, the source electrodes were placed at the dorsal surface of the third metacarpal bone of both hands and the dorsal surface of the third metatarsal bone of both feet, and the detector electrodes were placed at the acromion process of both shoulders and the greater trochanter of both femurs. Using this arrangement, the BI values of five parts of the trunk, both sides of the upper region, the middle region, and both sides of the lower region, were obtained and then used to calculate the whole trunk BI value and BI index (BI index(TR)). In the validation group, a simple regression analysis of the relationship between BI index(TR) and MVMRI showed a significant correlation between the two variables (r similar to 0.884, P similar to 0.05) and produced a prediction equation with a SE of estimation of 1,020.3 cm(3) (8.5%). In the validation and cross-validation groups, there were no significant differences between the measured and estimated MV without systematic errors. These findings indicate that the segmental BI analysis employed in the present study can be used to estimate trunk MV.

This study aimed to investigate the effects of age and gender on the power generation capabilities of lower limb muscles in the elderly aged from 65 to 79 yrs. In addition to isometric knee extension torque (KT) and leg extension power (LP), mechanical power during movements specific to maximal walking (WP) and running (RP) without arm movements were determined using a non-motorized treadmill in 140 men (71.3±4.0 yrs, mean±SD) and 172 women (70.2±3.7 yrs). The measured variables were expressed as relative to body mass and then their percentages to mean values for the subjects aged 65 to 69 yrs of men and women, respectively, were calculated. The percentages of all measured variables except for KT in the women were negatively correlated to age in both men (r=-0.207 to -0.375, p<0.05) and women (r=-0.228 to -0.263, p<0.05). In the slope of regression line for the relationship between age and the percentage for each of LP, WP, and RP, no significant differences were found between the men and women and between the variables. In the sub-sample of the subjects, adjusted by their body height and mass, the men (n=31) showed significantly higher values than the women (n=34) in all variables except for WP, with a greater relative difference in LP and RP than in KT. The findings obtained here indicate that, at least in the elderly aged from 65 to 79 yrs, 1) the rate of age-related loss in the power generation capability of lower limb muscles is independent of gender and movement patterns, and 2) power development in the movement form of maximal walking is less influenced by gender as compared to that of maximal running as well as knee extension torque and leg extension power.

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.

This study investigated the effect of gender on age-related changes in muscle thickness (Mt) in the elderly, with relation to the differences due to the location of muscle groups. Mt values at the forearm, upper arm anterior and posterior, abdomen, subscapular, thigh anterior and posterior, and lower leg anterior and posterior were determined using ultrasonography in 188 men and 204 women aged 65 to 79 yrs. The men had thicker muscles than the women, with a greater relative difference in the upper limb and trunk compared to the lower limb muscles. For the men, Mt values at the upper limb, thigh and abdomen were negatively correlated to age (r =-0.330 to -0.214, p<0.05). For the women, only the Mt at the thigh anterior showed a significant negative correlation with age (r =-0.346, p<0.05). At the thigh anterior, there was no significant difference between both genders in the slope of the regression line for the relationship between age and percentages of Mt to the mean value for the subjects aged 65 to 69 yrs of men and women, respectively, suggesting that the rate of the age-related loss of Mt at this site was independent of gender. These results were the same even when Mt was expressed as the value relative to (body mass)^1/3, calculated to normalize the influence of the difference in body mass. The findings obtained here indicated that, in an age span from 65 to 79 yrs, 1) gender difference in muscle thickness was more apparent in the upper limb and trunk than in the lower limb muscles, and 2) men showed significant age-related losses in muscle thickness at more body sites as compared to women, especially at the upper limb and abdomen.

Kubo, K., H. Kanehisa, and T. Fukunaga. Influences of repetitive drop jump and isometric leg press exercises on tendon properties in knee extensors. J. Strength Cond. Res. 19(4): 864-870. 2005.-The present study aimed to investigate the effects of repetitive drop jumps (DJ) and isometric leg presses (LP) on the tendon properties in knee extensors. Before and after each endurance test, the elongation (L) of the tendon and aponeurosis of the vastus lateralis muscle was measured directly by ultrasonography while the subjects performed ramp isometric knee extensions up to maximum voluntary isometric contraction. Eight men performed 100 repetitions of the DJ and 50 repetitions of the LP for 10 seconds with 10 seconds relaxation. In the DJ, there were no significant differences in L values at any force production levels before and after each endurance test. In LP, however, the L values above 500 N were significantly greater after the endurance test than before. These results suggest that the tendon properties in knee extensors change to become more compliant after the repeated longer-duration contractions, but not after repeated ballistic exercises.

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.

The purpose of this study was to investigate whether the mechanical properties of the Achilles tendon were correlated to muscle strength in the triceps surae in humans. Twenty-four men and twelve women exerted maximal voluntary isometric plantar flexion (MVIP) torque. The elongation (Delta X) and strain of the Achilles tendon (epsilon), the proximal part of which is the composite of the gastrocnemius tendon and the soleus aponeurosis, at MVIP were determined from the displacement of the distal myotendinous junction of the medial gastrocnemius using ultrasonography. The Achilles tendon force at MVIP (F) was calculated from the MVIP torque and the Achilles tendon moment arm. There were no significant differences in either the F-Delta X or F-epsilon relationships between men and women. Delta X and epsilon were 9.8 +/- 2.6 mm and 5.3 +/- 1.6%, respectively, and were positively correlated to F (r = 0.39, P &lt; 0.05; r = 0.39, P &lt; 0.05), which meant that subjects with greater muscle strength could store more elastic energy in the tendon. The regression gamma-intercepts for the F-Delta X (P &lt; 0.01) and F-epsilon (P &lt; 0.05) relationship were significantly positive. These results might indicate that the Achilles tendon was stiffer in subjects with greater muscle strength, which may play a role in reducing the probability of tendon strain injuries. It was suggested that the Achilles tendon of subjects with greater muscle strength did not impair the potential for storing elastic energy in tendons and may be able to deliver the greater force supplied from a stronger muscle more efficiently. Furthermore, the difference in the Achilles tendon mechanical properties between men and women seemed to be correlated to the difference in muscle strength rather than gender.

The aim of the present study was to examine the effects of viscoelastic properties of human tendon structures during stretch-shortening cycle exercise. The elongation of tendon and aponeurosis of the medial gastrocnemius muscle of 26 participants was measured by ultrasonography while they performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force and tendon elongation during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the muscle force-tendon elongation loop relative to the area beneath the curve during the ascending phase was defined as hysteresis. In addition, maximal voluntary concentric contractions at 2.09 and 3.14 rad center dot s(-1) with and without prior eccentric contractions were performed. The difference in the concentric torque at equivalent joint angles with and without prior eccentric contractions (i.e. pre-stretch augmentation) was negatively correlated with stiffiness (P &lt; 0.05) and hysteresis (P &lt; 0.05). Furthermore, there was a higher correlation between the pre-stretch augmentation and the viscoelastic properties index - that is, the sum of normalized score values of stiffness and hysteresis (P &lt; 0.01) - than with either stiffness or hysteresis alone. The results of this study suggest that performance during stretch-shortening cycle exercise is significantly affected by the viscoelastic properties of the tendon structures.

The purpose of the present study was to determine the in vivo passive mechanical properties, including the length below the slack length, of the gastrocnemius muscle (GAS) belly in humans. Transverse ultrasound images of the medial head of the GAS were taken in 11 subjects during passive knee extension from 80 degrees to 5 degrees with a constant ankle joint angle of 10 degrees (0 degrees is the neutral ankle position: positive values for dorsiflexion). The change in passive ankle joint moment (Mp), which is produced only by the GAS length change, was also measured during passive knee extension. The onset of Mp during passive knee extension was found to be 43 +/- 8 degrees (mean +/- SD) when the baseline of the Mp was set at the average Mp in the range of 55-60 degrees where the Mp was almost constant (SD &lt; 0.03 Nm). At this onset, the muscle fascicle length of the GAS (Lf) was 46 +/- 7 mm (slack length; Lfs). Lf at 80 degrees was 6 4 mm (13 +/- 6%) less than the Lfs, and Lf at 5 degrees was 12 5 mm (27 +/- 11%) greater than the Lfs. The passive force-resisting compression of the GAS did not produce a dorsiflexion moment in the joint angle range adopted. The passive ankle joint moment increased linearly with Lf (coefficient of determination (R-2) = 0.85-0.96), and the slopes of the relationships between Lf and Mp, and between the relative Lf to Us and Mp were 0.093 +/- 0.038 Nm/mrn and 0.043 +/- 0.021 Nm/%Lfs. The findings of the present study can be implemented in musculoskeletal modeling, which would provide a more accurate evaluation of the passive mechanical properties of muscle during movement. (c) 2004 Elsevier Ltd. All rights reserved.

The purposes of this study were to compare the elasticity of tendon and aponeurosis in human knee extensors and ankle plantar flexors in vivo and to examine whether the maximal strain of tendon was correlated to that of aponeurosis. The elongation of tendon and aponeurosis during isometric knee extension (n = 23) and ankle plantar flexion (n = 22), respectively, were determined using a real-time ultrasonic apparatus, while the participants performed ramp isometric contractions up to voluntary maximum. To calculate the strain values from the measured elongation, we measured the respective length of tendon and aponeurosis. For the knee extensors, the maximal strain of aponeurosis (12.1 &PLUSMN; 2.8%) was significantly greater than that of the patella tendon (8.3 &PLUSMN; 2.4%), p &LT; 0.001. On the contrary, the maximal strain of Achilles tendon (5.9 &PLUSMN; 1.4%) was significantly greater than that of aponeurosis in ankle plantar flexors (2.7 &PLUSMN; 1.4%), p &LT; 0.001. Furthermore, for both knee extensors and ankle plantar flexors there was no significant correlation between maximal strain of tendon and aponeurosis. These results would be important for understanding the different roles of tendon and aponeurosis during human movements and for more accurate muscle modeling.

This study tested the hypothesis that, as compared to whole-body bioelectrical impedance (BI) analysis, segmental BI analysis can estimate lean body mass (LBM) more accurately in a population with a large difference in muscularity. In addition to whole-body BI, which determines impedance (Z) between the wrist and ankle, two segmental BI analyses which determine the Z value of every body segment in each of (1) the arms, legs and trunk (distal BI) and (2) the upper arms, upper legs and trunk (proximal BI) were applied to a group of 125 male athletes and 75 non-athletes. The subjects were divided into validation and cross-validation groups. Simple and multiple regression analyses were applied to (length)(2)/Z (BI index) values for the whole-body and each body segment, to develop the prediction equations of LBM measured using air-displacement plethysmography. In the validation group, the SE of estimation was similar in the whole-body (3.4 kg, 5.4%), distal (3.4 kg, 5.5%) and proximal BI (3.3 kg, 5.2%) analyses. However, the whole-body and distal BI analyses produced systematical errors in the estimates of LBM. Moreover, the residuals in the two methods significantly (P &lt; 0.05) correlated with the ratios of BI indices of the upper arms and upper legs to those of the arms and legs, respectively, calculated as variables approximating the relative development of lean tissues at the proximal area of limbs. On the other hand, the proximal BI analysis was validated and cross-validated. Thus, the accuracy of estimating LBM was similar in the whole-body and the two segmental BI analyses. However, the prediction equations derived from the use of the whole-body BI index and a combination of the arms, legs and trunk BI indices produced a systematical error relating to the difference between the limb segments in lean tissue development.

It has been suggested that a suppression of maximal voluntary contraction (MVC) induced by prolonged vibration is due to an attenuation of Ia afferent activity. The purpose of the present study was to test the hypothesis that aftereffects following prolonged vibration on muscle activity during MVC differ among plantar flexor synergists owing to a supposed difference in muscle fiber composition. The plantar flexion MVC torque and surface electromyogram (EMG) of the medial head of gastrocnemius (MG), the lateral head of gastrocnemius (LG), and the soleus ( Sol) were recorded in 13 subjects before and after prolonged vibration applied to the Achilles tendon at 100 Hz for 30 min. The maximal H reflexes and M waves were also determined from the three muscles, and the ratio between H reflexes and M waves (H/Mmax) was calculated before and after the vibration. The MVC torque was decreased by 16.6 +/- 3.7% after the vibration ( P &lt; 0.05; ANOVA). The H/Mmax also decreased for all three muscles, indicating that Ia afferent activity was successfully attenuated by the vibration in all plantar flexors. However, a reduction of EMG during MVC was observed only in MG (12.7 +/- 4.0%) and LG (11.4 +/- 3.9%) ( P &lt; 0.05; ANOVA), not in Sol (3.4 +/- 3.0%). These results demonstrated that prolonged vibration-induced MVC suppression was attributable mainly to the reduction of muscle activity in MG and LG, both of which have a larger proportion of fast-twitch muscle fibers than Sol. This finding suggests that Ia-afferent activity that reinforces the recruitment of high-threshold motor units is necessary to enhance force exertion during MVC.

Background Cooling and heating have been shown to affect the contractile properties of muscles. However, the reasons for these changes remain unclear. The present study aimed to quantify the mechanical properties of muscle and tendon during passive stretch and active contraction, and to investigate the effects of cooling and heating on the mechanical properties of muscle and tendon.
Methods. Before and after these conditions, the elongation of the muscle fascicle, tendon and aponeurosis of the medial gastrocnemius muscle was directly measured by ultrasonography, while the ankle joint was passively moved within the joint range of + 15 to -30 deg (0 deg = neutral anatomic position; positive values for plantar flexion) and subjects performed ramp isometric plantar flexion up to the voluntary maximum.
Findings. While the muscle fascicle, tendon and aponeurosis stretched during passive dorsi-flexion, the elongation of the tendon was significantly greater than that of the aponeurosis. During isometric contraction, the maximal elongation of the tendon was significantly greater than that of the aponeurosis. After cooling and heating, no significant changes in the elongation of muscle fascicle, tendon and aponeurosis were found during passive stretch. Similarly, after both the immersions there were no changes in the relationship between the estimated muscle force and elongation of each structure (tendon-aponeurosis complex, tendon) during isometric contraction.
Interpretation. These results implied that the general application of icing and hot pack did not change the mechanical properties of muscle and tendon. (C) 2004 Elsevier Ltd. All rights reserved.

Aim. This study aimed to investigate the muscularity of strength-trained junior athletes.
Methods. Muscle thickness (Mt) values at 10 sites (anterior forearm, anterior upper arm, posterior upper arm, chest, abdomen, back, anterior thigh, posterior thigh, anterior lower leg, and posterior lower leg) were determined in junior Olympic weight lifters (OWL, n=7,15.1 +/- 0.3 y, mean +/- SD) and non-athletes (CON, n=13,15.1 +/- 0.3 y) using a brightness mode ultrasonography. Skeletal age assessed with the Tanner-Whitehouse 11 method (20 hand-wrist bones) was similar in OWL (16.4 +/- 0.7 y) and CON (16.3 +/- 0.6 y).
Results. At the 6 sites (anterior forearm, anterior upper arm, posterior upper arm, chest, back and anterior thigh), OWL showed significantly greater Mt values than CON even in terms of Mt relative to (body mass)(1/3) (Mt(.)BM(-1/3)). On the other hand, there were no significant differences between the 2 groups in the Mt ratios of the anterior to posterior site in the upper arm, thigh and lower leg and those of the back to either the chest or abdomen in the trunk. For OWL only, skeletal age was significantly correlated to Mt(.)BM(-1/3) at the abdomen (r=0.869, p &lt; 0.05) and anterior thigh (r=0.883, p &lt; 0.05).
Conclusion. The findings here indicate that 1) as compared to adolescent non-athletes, junior Olympic weight lifters show a greater muscularity in the upper body and anterior thigh without predominant development in either of anterior and posterior sites within the same body segment, 2) for junior Olympic weight lifters, the muscularity of abdominal and knee extensor muscles is influenced by the biological maturation.

This study estimated the passive ankle joint moment during standing and walking initiation and its contribution to total ankle joint moment during that time. The decrement of passive joint moment due to muscle fascicle shortening upon contraction was taken into account. Muscle fascicle length in the medial gastrocnemius, which was assumed to represent muscle fascicle length in plantarflexors, was measured using ultrasonography during standing, walking initiation, and cyclical slow passive ankle joint motion. Total ankle joint moment during standing and walking initiation was calculated from ground reaction forces and joint kinematics. Passive anklejoint moment during the cyclical ankle joint motion was measured via a dynamometer. Passive ankle joint moment during standing and at the time (Tp) when the MG muscle-tendon complex length was longest in the stance phase during walking initiation were 2.3 and 5.4 Nm, respectively. The muscle fascicle shortened by 2.9 mm during standing compared with the length at rest, which decreased the contribution of passive joint moment from 19.9% to 17.4%. The muscle fascicle shortened by 4.3 mm at Tp compared with the length at rest, which decreased the contribution of passive joint moment from 8.0% to 5.8%. These findings suggest that (a) passive ankle joint moment plays an important role during standing and walking initiation even in view of the decrement of passive joint moment due to muscle fascicle shortening upon muscle contraction, and (b) muscle fascicle shortening upon muscle contraction must be taken into account when estimating passive joint moment during movements.

We tested the possible usefulness of new evaluation methods of the effects of exercise intervention on the medical economy, focusing on medical costs of the elderly who participated in the exercise group compared with control subjects (or estimated values) in four local self-governing bodies. In village A we compared the yearly medical costs between 20 participants of the exercise group (aerobics and muscle exercise using a weight machine) and 20 control subjects. We compared not only yearly medical costs but also cumulative medical costs from the entry year. In city B, we compared the medical costs of May of each year between 74 participants of the exercise group (aerobics and muscle exercise using their own body weights) and 210 control subjects. We compared not only the medical costs of each May but also the cumulative medical costs from the previous periods. In town C we compared the medical costs of each May between 16 participants of an exercise group (muscle exercise using their own body weights), 23 participants of another exercise group (exercise using exercise balls), 8 quoits players, and 46 control subjects, using cumulative costs. In ward D we tried estimating values of the controls calculated from the entire medical costs of the national health insurance system, and compared the medical costs of 13 participants of the exercise group (muscle exercise using their own body weights) and the estimated values, using cumulative costs. Results show that the cumulative medical costs of the control subjects increased more than the exercise groups in village A. Similar tendencies were shown in cumulative medical costs of May of each year in city B, town C, and ward D. In conclusion cumulative medical costs might be useful for evaluating the effects of exercise on the medical economy.

To examine the origin of mechanomyogram (MMG), we compared the responses of surface MMG with the changes in the fascicle length determined by ultrasonography during electrically induced contractions of human skeletal muscles. The posterior tibial nerve of subjects (n=5) was stimulated with a stimulus pattern in which the frequency rose up from 1Hz to 20Hz linearly. The MMG amplitude decreased with increasing stimulation frequency. Reduction of MMG amplitude was in parallel with the decrease in fluctuation of the changes in fascicle length, and these values had a significant positive correlation (r=0.94, P<0.001). The observed direct relation between MMG and architectural change of muscle indicates that surface MMG is generated by the pressure wave produced by the expansion of a number of muscle fibers during contractions.

The purpose of this study was to investigate the effects of passive ankle and knee joint motions on the length of fascicle and tendon of the gastrocnemius muscle. The ankle joint was passively moved from maximal dorsiflexed position to maximal plantar flexed position, while the knee joint was fixed at 0° (fully extended position). Also, the knee joint was passively extended from 90° to 0°, while the ankle joint was fixed at 0° (neutral position). In each test condition, lengths of fascicle and external tendon of the medial gastrocnemius were measured by ultrasonography. The length of external tendon was significantly changed by the ankle joint motion, but not by the knee joint motion. This demonstrates that the length of the external tendon distal to the muscle belly is influenced only by the angle changes of the joint distal to the gastrocnemius muscle. The change in fascicle length during the knee joint motion was significantly larger than during the ankle joint motion in spite of a similar length change of total muscle-tendon complex between the two motions. This demonstrates that fascicles located proximally to the external tendon are more influenced by the angle changes of the joint proximal to the gastrocnemius muscle. These results reveal that angle changes of each joint located in the proximal and distal parts of a biarticular muscle have different effects on the length of fascicle and external tendon.

This study aimed to investigate the mechanisms of mechanical work and power enhancement of muscle-tendon complex (MTC) in rebound exercise by quantifying in vivo behavior of fascicle and tendinous tissue of human medial gastrocnemius muscle (MG). Subjects jumped on a sledge apparatus using only ankle joint with the following two conditions: plantar flexion without counter movement (PFJ) and rebound jumping from a height of 26 cm (RJ). The behavior of fascicle and tendinous tissue of MG in vivo was determined using ultrasonography. The relative contribution of tendinous tissue to the mechanical work of MTC during plantar flexion phase (PF phase) was 85% in RJ. The maximal mechanical power of tendinous tissue during the PF phase in RJ was about three times greater compared to that in PFJ. There was no significant difference in the mechanical power of fascicle during PF phase between the two conditions, while the mechanical work of fascicle in PFJ was less than that in the PF phase of RJ. In RJ, fascicle was stretched during the dorsiflexion phase. These findings indicated that, in rebound exercise using ankle joint, (1) the enhancement of mechanical work and power of MTC was due to the reuse of elastic energy stored in tendinous tissue during dorsiflexion phase, and (2) fascicles were stretched during dorsiflexion phase.

This study aimed to investigate the behavior of the aponeurosis and external tendon of the medial gastrocnemius muscle (MG) in dynamic actions. Seven males performed maximal and submaximal concentric (CON) and eccentric (ECC) plantar flexion exercises preceded by an isometric action (Pre-iso) on an isokinetic dynamometer at a pre-set velocity of 5°/s. In addition, the subjects performed static ramp actions with the ankle positioned at dorsi-and plantar flexed positions. During the exercises, the length changes of the aponeurosis and external tendon of MG were determined using ultrasound apparatuses. In CON, the length of external tendon significantly shortened from the level of Pre-iso in all test conditions. However, the change of aponeurosis was significant only in the maximal exercises. In ECC, the external tendon was elongated in all test conditions, while the aponeurosis was not elongated even in the maximal effort. In static action, the lengths of both aponerurosis and external tendon increased with increasing force levels. The present results indicate that the behavior of aponeurosis of MG depends on the type of action and that the aponeurosis of MG plays a simple role of muscle force transmission in eccentric actions, while external tendon functions to store elastic energy.

The present study aimed to determine the differences in the length-force relationship between muscle fiber and muscle tendon complex (MTC) and to relate the shape of the length-force relationship to the architectural changes in MTC (the elongation of tendon structures and pennation angle changes). In six male subjects, tetanic contractions (2s at 50Hz) of the tibialis anterior muscle were induced electrically. At a steady state of tetanic contraction, the muscle fiber length and pennation angle were measured from ultrasonic images, and the muscle fiber force, tendon force, MTC length and elongation of tendon structures were calculated. The measured and normalized length-force relationships were clearly different between muscle fiber and MTC, especially on the length axis. The differences could be attributed to the existence of compliant tendon structures and increment of pennation angles related to elongation of tendon structures, suggesting that compliant tendon structures in human muscles influence the length-dependent force generation in both muscle fiber and MTC.

The purpose of this study was to examine the differences in the geometric and elastic properties of the Achilles tendon between right and left ankles in kendo (japanese fencing) athletes, who engaged in kendo training for years, and matched controls. The subjects were twelve kendo athletes and nine controls (21 and 20 yrs, 65 and 60 kg, and 172 and 171 cm, respectively). While the subjects developed maximum voluntary isometric plantarflexion (MVIP) torque (TQ), the tendon displacement and ankle joint rotation was determined using a B-mode ultrasonograph and a goniometer, respectively. The tendon force (F) was calculated from TQ and the moment arm of the Achilles tendon. The elongation of the Achilles tendon (ΔX) was obtained from the tendon displacement and ankle joint rotation. The cross-sectional area of the Achilles tendon (CSA) was measured using a B-mode ultrasonography. The Achilles tendon stiffness (k) was defined as F divided by ΔX, stress (σ) as F divided by CSA, strain (ε) at MVIP as ΔX divided by the Achilles tendon length at rest (Lr), and Young's modulus (E) as σ divided by ε. The results showed that there were no significant differences in TQ, F, σ, Lr, ΔX, ε, k, and E between right and left ankles for both control and kendo athlete subjects, and between control and kendo athlete subjects. CSA of kendo athletes' right ankles was significantly greater than that of kendo athletes' left ankles (p=0.03). It was suggested that a long-term kendo training did not affect the elastic properties of the Achilles tendon and resulted in smaller Achilles tendon CSA in left ankles.

The fascicle lengths of the human gastrocnemius muscle during isometric plantar flexions were analyzed using a three-dimensional ultrasound system (3D-US). Prior to measurements in vivo, the accuracy and reproducibility of the 3D-US were examined by taking images of a phantom. The horizontal errors were 0.3-1.0%, and the vertical errors were 1.2-1.6%. In addition, the coefficients of variance for the repeated measurements were 3.3% and 1.7% for horizontal and vertical directions, respectively. Second, both at rest and each of five intensities {20, 40, 60, 80, 100% of maximum voluntary contraction (MVC)}, at a fixed ankle joint angle of 90deg, the 3D-US images of gastrocnemius muscles were obtained and used to determine fascicle length. The fascicle length was also measured using two-dimensional ultrasound system (2D-US), and the values obtained by 2D-US were used to make comparisons with those by 3D-US. From rest to MVC, the fascicle length decreased as a function of relative torque levels from 6.0 (± 0.5) cm to 3.1 (± 0.4) cm with 3D-US, and, in a similar manner, from 5.6 (± 0.5) cm to 3.0 (± 0.4) cm with 2D-US. Thus the present study indicated the accuracy and reproducibility of the 3D-US measurements and its usefulness for determining the fascicle lengths of human muscles in three-dimensional space. The fascicle length measurements determined by 3D-US were, however, significantly longer than those of 2D-US.

Flexibility is often evaluated from the joint range of motion (ROM), but the mechanisms underlying gender differences in joint ROM have not been elucidated. The purpose of this study was to investigate the factors influencing the difference in ankle joint ROM between men and women with respect to the extensibility of muscle-tendon complex. Eighteen men (21-26 yr, 66.4±6.0kg, 173.7±7.4cm mean±SD) and 12 women (19-27yr, 52.9±4.8kg, 163.4±4.3cm) participated in this study. Each subject was seated with the knee extended, and the ankle joint was attached to a foot plate, by which the ankle joint was passively dorsiflexed with torque gradually increasing from zero to a value at which the passive loading to the ankle joint was just tolerable for each subject. During the passive loading, real-time ultrasonogram was taken to track the movement of MTJ (muscle-tendon junction of the gastrocnemius medialis and Achilles tendon) as the elongation of muscle belly (dMus). The change of MTC (muscle-tendon complex) length (dMTC) during the passive dorsiflexion was estimated from changes in ankle joint angle. Tendon elongation (dTen) was calculated by subtracting dMus from dMTC. There was no significant difference in normalized passive torque during passive dorsiflexion between men and women. Women were more flexible, i.e., they demonstrated greater dMTC, which was accompanied by greater dTen at lower torque levels. However, dMus was not different between men and women. It was concluded that gender difference in the joint ROM at the ankle reflects more compliant Achilles tendon in women than in men.

The purpose of the study was to examine the effect of prolonged vibration on the force fluctuations during a force-matching task performed at low-force levels. Fourteen young healthy men performed a submaximal force-matching task of isometric plantar flexion before and after Achilles tendon vibration (n = 8, vibration subjects) or lying without vibration (n = 6, control subjects) for 30 min. The target forces were 2.5-10% of the previbration maximal voluntary contraction force. The standard deviation of force decreased by a mean of 29 +/- 20% across target forces after vibration, whereas it did not decrease significantly in control subjects (-5 +/- 12%). This change was significantly greater compared with control subjects (P &lt; 0.01 for both). Power spectral density of the force was predominantly composed of signals of low-frequency bandwidth (&LE;5 Hz) with few higher frequency components. In vibration subjects, there was a significant decrease in power in the frequency range &LE;2 Hz after vibration. The decrease in power at this frequency range was linearly related to the decrease in the force fluctuations (r = 0.96, P &lt; 0.001). The results indicate that prolonged Achilles tendon vibration reduces the fluctuations in plantar flexion force in the frequency range less than or equal to2 Hz during low-level contractions. It suggests that Ia afferent inputs contribute to the low-frequency force fluctuations in plantar flexion.

The study examined the hypothesis that altered synergistic activation of the knee extensors leads to cyclic modulation of the force fluctuations. To test this hypothesis, the force fluctuations were investigated during sustained knee extension at 2.5% of maximal voluntary contraction force for 60 min in 11 men. Surface electromyograms (EMG) were recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles. The SD of force and average EMG (AEMG) of each muscle were calculated for 30-s periods during alternate muscle activity. Power spectrum of force was calculated for the low- (less than or equal to3 Hz), middle- (4-6 Hz), and high-frequency (8-12 Hz) components. Alternate muscle activity was observed between RF and the set of VL and VM muscles. The SD of force was not constant but variable due to the alternate muscle activity. The SD was significantly greater during high RF activity compared with high VL and VM activity (P &lt; 0.05), and the correlation coefficient between the SD and AEMG was significantly greater in RF [0.736 (SD 0.095), P &lt; 0.05] compared with VL and VM. Large changes were found in the high-frequency component. During high RF activity, the correlation coefficient between the SD and high-frequency component [0.832 (SD 0.087)] was significantly (P &lt; 0.05) greater compared with other frequency components. It is suggested that modulations in knee extension force fluctuations are caused by the unique muscle activity in RF during the alternate muscle activity, which augments the high-frequency component of the fluctuations.

The purpose of this study was to investigate the effects of resistance training on the tendon properties in knee extensors during 20 days of bed rest. Sixteen men were assigned to the resistance training group (BR-Tr) or the non-training, control group (BR-Con). Leg-press exercises were performed as five sets of 10 repetitions at 90% of maximum load daily for 20 days during bed rest. Before and after bed rest, the elongation of the tendon structures of the vastus lateralis muscle during isometric knee extension was determined using ultrasonography, while subjects performed ramp isometric contraction up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force (F-m) and tendon elongation (L) was fitted to a linear regression curve, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the F-m-L loop to the area beneath the load portion of the curve. The stiffness decreased significantly after bed rest for BR-Con, but not for BR-Tr. Similarly, the hysteresis increased significantly after bed rest for BR-Con, but not for BR-Tr. These results suggested that the bed rest caused the stiffness of tendon structures to decrease and their hysteresis to increase, and that leg-press training prevents the deconditioning of the tendon structures in knee extensors.

The purpose of this study was to investigate the effect of 20 days of bed rest (BR) on the physiological cross-sectional area (PCSA) of the adductor (AD) muscle group. Five healthy men and five healthy women were kept on a horizontal bed for 20 days. To calculate the PCSA of the AD muscle group, transaxial magnetic resonance imaging of the right thigh was acquired four times for each of the subjects: (1) pre BR, (2) on the tenth day of BR, (3) post BR, and (4) 1 month after BR. Overall, the PCSA measurements of the AD muscle group and its individual muscles were significantly decreased on the tenth day of BR and at post BR; however, they had recovered to the baseline within 1 month of the reambulation period. The amount and pattern of relative change in the PCSA measurements of the AD muscle group were similar to those of the knee extensor (KE) and knee flexor (KF) muscle groups studied previously. These results suggested that the AD muscle group showed an atrophic response that was similar to the KE and KF muscle groups after unweighting; therefore, we should pay much more attention to the AD muscle group when considering countermeasures for future human spaceflight projects.

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly (P&lt;0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P&lt;0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.

Objectives: The purpose of this study was to investigate the effects of 20 days' bed rest on the viscoelastic properties of human tendon structures in knee extensor and plantar flexor muscles in vivo.
Methods: Eight healthy men ( age: 24 4 years, height: 172 9 m, body mass: 69 13 kg) carried out a 6 head-down bed rest for 20 days. Before and after bed rest, elongation ( L) of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and plantar flexion, respectively, were determined using real-time ultrasonic apparatus, while the subjects performed ramp isometric contraction up to the voluntary maximum, followed by ramp relaxation. The relationship between estimated muscle force (Fm) and tendon elongation ( L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the Fm-L loop to the area beneath the load portion of the curve.
Results: L values above 100 N were significantly greater after bed rest for VL, while there were no significant differences in L values between before and after for MG. The stiffness decreased after bed rest for VL (70.3 +/- 27.4 v 50.1 +/- 24.8 N/mm, before and after bed rest, respectively; p = 0.003) and MG (29.4 +/- 7.5 v 25.6 +/- 7.8 N/mm, before and after bed rest, respectively; p = 0.054). In addition, hysteresis increased after bed rest for VL (16.5 +/- 7.1% v 28.2 +/- 12.9%, before and after bed rest, respectively; p = 0.017), but not for MG (17.4 +/- 4.4% v 17.7 +/- 6.1%, before and after bed rest, respectively; p = 0.925).
Conclusions: These results suggested that bed rest decreased the stiffness of human tendon structures and increased their hysteresis, and that these changes were found in knee extensors, but not the plantar flexors.

This study aimed to examine the influences of circulatory difference on the utilization of O-2 and the progression of fatigue in the tibialis anterior (TA) muscle during dorsiflexion exercise, with reference to different body postures. The subjects performed intermittent static dorsiflexion at 50% of maximal voluntary contraction (MVC) up to exhaustion with the right leg either up or down relative to the heart. These exercises were performed with and without occluding muscle blood flow. Simultaneously with the surface electromyogram (EMG) measurement, total hemoglobin volume change and tissue oxygenation (StO2) of TA were measured using near-infrared spectroscopy (NIRS). When the subjects performed an exhaustive intermittent dorsiflexion exercise at 50% MVC, the endurance time decreased in the leg up position. Also, the progression of fatigue in TA detected using EMG signals (i.e. integrated EMG and mean power frequency of EMG) was faster with the leg elevated. The NIRS data indicated a lower blood volume and StO2 with the leg up than with the leg down during the exercise, which suggests that the deficit in the O-2 supply to exercising muscle's demand was more apparent in the leg up position. However, these differences in EMG and NIRS data disappeared when the blood flow was restricted in both positions. From these results it is concluded that the difference in exercising muscle oxygenation between two different body postures influenced the progression of muscle fatigue and caused the difference in endurance performance.

This study aimed to investigate the influences of age and sex on the thickness of the rectus abdominis muscle and subcutaneous fat at the abdomen. The two tissue thickness values were determined using ultrasonography in a total of 194 young (20-29 years) and elderly (70-79 years) persons of both genders. In both sexes, the elderly groups showed significantly thinner muscle and thicker fat than the younger groups. The percentage of the mean value of subcutaneous fat thickness in the elderly group compared to that in the younger group was higher in the women (176%) than in the men (128%), but the corresponding value of muscle thickness was similar between men (68%) and women (65%). In both generations, the women had significantly thinner muscle and thicker fat than the men. The percentage of the mean value of subcutaneous fat thickness in the women compared to that in the men was higher in the elderly group (169%) than in the younger group (123%), but the corresponding value of muscle thickness was similar between the younger (80%) and elderly (77%) groups. In every group, subcutaneous fat thickness significantly correlated with waist circumference, but muscle thickness did not. The findings here indicated that: (1) aging was associated with a decrease of muscle thickness and an increase of subcutaneous fat at the abdomen in men and women, with a similar relative loss of muscle thickness in both genders and a greater increase of subcutaneous fat thickness in women than in men, and (2) subcutaneous fat rather than muscle thickness reflected waist circumference, regardless of age and gender.

Introduction: Few studies have attempted to investigate the influence of prolonged head-down bed rest (HDBR) on hypercapnic ventilatory chemosensitivity, and there are no data available regarding associated changes in arterial BP and heart rate (HR). The aim of this study was to clarify the influence of Prolonged HDBR on ventilatory and cardiovascular responses to hypercapnia. Methods: There were five healthy men who participated in this study. Resting ventilatory and cardiovascular responses to hypercapnia were measured by means of Read's CO2 rebreathing method 4 d before and on the 19th day of HDBR. Measured variables included systolic and diastolic BP (SBP and DBP, respectively), inspired minute ventilation V-t, and end-tidal partial pressure of CO2 (PETCO2). Results: Ventilatory response to hyperoxic hypercapnia (DeltaV(t)/ DeltaPETCO(2)) decreased significantly on the 19th day of HDBR (1.42 +/- 0.65 to 0.90 +/- 0.41 L . min(-1) . torr(-1), p &lt; 0.05). On the other hand, SBP, DBP, and HR responses (DeltaSBP/DeltaPETCO(2), DeltaDBP/DeltaPETCO(2), and DeltaHR/ DeltaPETCO(2)) were unchanged. Discussion: The results from this study suggest that prolonged HDBR leads to diminished central hypercapnic ventilatory chemosensitivity.

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.

The purpose of this study was to investigate the influence of different angles of the knee joint on the activation level of an agonist (quadriceps femoris muscle) and antagonist (biceps femoris muscle) from electromyographic activities and activation levels (twitch interpolation). Isometric torque measurements were performed on 23 healthy subjects at 10degrees intervals between 40degrees and 110degrees of knee joint flexion. Superimposed twitches at maximal voluntary contraction were applied and the voluntary activation estimated. To quantify the antagonist muscle activity, we normalized its integrated EMG (iEMG) value at each joint angle with respect to its iEMG value at the same angle when acting as an agonist at maximal effort. The activation levels at the knee-flexed position (80-110degrees) were higher than that at the knee-extended position (40-70degrees). The co-activation levels at 90, 100, and 110degrees were significantly higher than that the other knee angle. These results suggest that the activation level of an agonist (quadriceps femoris) muscle and the co-activation level of an antagonist (biceps femoris) muscle were higher in longer muscles than in shorter muscles. It was also concluded that the risk of knee injuries could be reduced by applying these mutual relationships between activation levels of agonist and antagonist muscles.

The purpose of this study was to clarify the influence of muscle-tendon complex stretch on electromechanical delay (EMD) in terms of the extent of tendon slack in the human medial gastrocnemius (MG). EMD and MG tendon length were measured at each of five ankle joint angles ( - 30, - 20, - 10, 0, and 5degrees: positive values for dorsiflexion) using percutaneous electrical stimulation and ultrasonography, respectively. The extent of MG tendon slack was calculated as MG tendon length shortening, standardized with MG tendon slack length obtained at the joint angle (-16degrees +/- 5degrees) where the passive ankle joint torque was zero. EMD at - 30degrees (19.2 +/- 2.2 ms) and - 20degrees (17.2 +/- 1.3 ms) was significantly greater than that at - 10degrees (16.0 +/- 2.3 ms), 0degrees (15.0 +/- 1.4 ms), and 5degrees (14.8 +/- 1.4 ms), and at 0 and 5degrees, respectively. The relative EMD, normalized with the maximal EMD for each subject, decreased dependent on the extent of decrease in MG tendon slack. There were no significant differences in EMD among the joint angles (-10, 0, and 5degrees) where MG tendon slack was taken up. These results suggest that the extent of tendon slack is an important factor for determining EMD.

The present study aimed to investigate the level of muscular activities such as postural maintenance and change, and body weight transfer during daily physical activities, through electromyogram (EMG) recordings. In each of 27 prescribed movements, EMGs of a total of 8 muscles located in the upper arms, trunk and lower limbs were recorded in 12 young adult men and women using a portable surface electromyograph apparatus. The percentage of integrated EMG per time (mEMG) to that during isometric maximum voluntary contraction (MVC) was calculated as an index by assessing the muscular activity level in each of the prescribed movements. In most of the prescribed movements, the muscular activity level of every muscle corresponded to about 20〜30% of MVC, and tended to be higher in women than men. However, some actions induced an activity level of 40% and more of MVC in the soleus muscle. The activity levels of the lower limb muscles in going up and down stairs and a slope at a fast speed, and jogging were higher compared to other prescribed movements. Thus, the results indicate that body weight transfer actions in daily life raise the activities of the lower limb muscles to a level sufficient for maintaining and increasing their function.

The purpose of this study was to clarify whether the major determinant of the extendibility of the Achilles tendon in young adults was the geometric properties of the tendon. The subjects were 38 healthy young adults (26 male, 12 female; 26 5 years). The subjects developed maximum voluntary isometric plantar flexion (MVIP) torque while the displacement of the distal myotendinous junction of the medial gastrocnemius and ankle joint rotation was determined using a B-mode ultrasonograph and a goniometer, respectively. The tendon force (F) was calculated from MVIP torque and the moment arm of Achilles tendon. The elongation of the Achilles tendon (Delta X) was obtained from the tendon displacements and ankle joint rotation. Achilles tendon stiffness W was calculated by dividing F by Delta X The specific stiffness of the Achilles tendon (k(s)) was obtained from k normalized to the Achilles tendon length at rest. The cross-sectional area of the Achilles tendon (CSA) was measured at 5, 10, and 15% of the lower leg length proximal to the insertion of the Achilles tendon using a B-mode ultrasonography. The results showed that more distal portion of the Achilles tendon had a larger CSA, and that there was a strong correlation between the average and minimum Achilles tendon CSA. Delta X was 9.9 +/- 2.5 mm. k and k(s) were 330 +/- 77 N/mm and 63 +/- 20 kN, respectively. No significant correlation was seen between CSA and k(s) (r = 0.15, p &gt; 0.05). It was suggested that a stiffer Achilles tendon did not necessarily have a thicker shape, which might indicate that the major determinant of the extendibility of the Achilles tendon was not its geometric properties in young adults. Copyright (C) 2004 S. Karger AG, Basel.

Behavior of fascicles and tendinous structures of the in. gastrocnemius medialis (MG) was quantitatively examined during human jumping in vivo. Eight male subjects performed maximal-effort counter movement jumping (CMJ) motions. Kinematic and kinetic data were obtained using a high-speed camera and a force platform. Behavior of fascicles and tendinous structures was determined using ultrasonography and electromyography. Although the muscle-tendon complex (MTC) shortened by only 1.6% during the downward phase of the counter movement, fascicles shortened as much as 10.4%. This shortening of fascicles caused elongation of tendinous structures by 2.2%. Although the MTC remained at almost constant length during the upward-I phase (-250 to - 100 ms before toe-off), fascicles shortened by 19.2% of the initial length with an elongation of tendinous structures by 4.4%. The MTC shortened rapidly by 5.3% of the initial length during the upward-II phase (-100 to 0 ms), whereas fascicles shortened slightly during the first half of this phase and contracted in a quasi-isometric manner during the latter half of this phase. These findings implied that elastic energy was stored in tendinous structures throughout the latter half of the downward phase (1.0 J) and upward-I phase (5.6 J), which was thereafter rapidly released during the upward-II phase (3.8 J). It was found that muscle fibers of the MG were not stretched during counter movement; therefore, stretch reflex and potentiation of the contractile component of the MG might not contribute to the work enhancement in CMJ. It was suggested that the interaction between fascicles and tendinous structures was essential in a generation of higher joint power during the late push-off phase. This behavior of the MTC of the MG in CMJ was quite similar to what was observed in squat jumping performed without counter movement.

The purpose of the study was to determine the effect of bed rest with or without strength training on torque fluctuations and activation strategy of the muscles. Twelve young men participated in a 20-day bed rest study. Subjects were divided into a non-training group (BRCon) and a strength-training group (BRTr). The training comprised dynamic calf-raise and leg-press exercises. Before and after bed rest, subjects performed maximal contractions and steady submaximal isometric contractions of the ankle extensor muscles and of the knee extensor muscles (2.5-10% of maximal torque). Maximal torque decreased for both the ankle extensors (9%, P &lt; 0.05) and knee extensors (16%, P &lt; 0.05) in BRCon but not in BRTr. For the ankle extensors, the coefficient of variation ( CV) for torque increased in both groups (P &lt; 0.05), with a greater amount (P &lt; 0.05) in BRCon (88%) compared with BRTr (41%). For the knee extensors, an increase in the CV for torque was observed only in BRCon (22%). The increase in the CV for torque in BRCon accompanied the greater changes in electromyogram amplitude of medial gastrocnemius (122%) and vastus lateralis (59%) compared with BRTr (P &lt; 0.05). The results indicate that fluctuations in torque during submaximal contractions of the extensor muscles in the leg increase after bed rest and that strength training counteracted the decline in performance. The response varied across muscle groups. Alterations in muscle activation may lead to an increase in fluctuations in motor output after bed rest.

Objectives: To determine sex differences in the distribution of regional and total skeletal muscle (SM) using contiguous whole body magnetic resonance imaging (MRI) data, and to examine the relations between fat free mass (FFM) and total and regional SM masses.
Methods: A total of 20 Japanese college students (10 women and 10 men) volunteered for the study. FFM was measured by two compartment densitometry. Whole body MRI images were prepared using a 1.5 T scanner. Contiguous transverse images with 1.0 cm slice thickness were obtained from the first cervical vertebra to the ankle joints. All MRI scans were segmented into four components ( SM, subcutaneous adipose tissue, bone, and residual tissues). In each slice, the SM tissue cross sectional areas (CSAs) were digitised, and the muscle tissue volume per slice was calculated by multiplying muscle CSA by slice thickness. SM volume units (litres) were converted into mass units (kg) by multiplying the volumes by the assumed constant density (1.041 mg/ml) for SM.
Results: The SM distribution pattern (shape of curve) from the contiguous whole body slices was essentially similar for the two sexes, with two large peaks and three smaller peaks (arms excluded). However, the largest peak was observed at the upper portion of the thigh for women and at the level of the shoulder for men. Men had larger (p&lt;0.01) total and regional SM mass than women. All regional SM masses correlated highly (r = 0.90-0.99, p&lt;0.01) with total SM mass. A strong positive correlation was observed between FFM and total and regional SM masses in both sexes (women, r = 0.95; men, r = 0.90; all p&lt;0.01). As FFM increased, there was a corresponding increase in SM/FFM ratio for all subjects (r = 0.86, p&lt;0.01).
Conclusions: Sex differences in total SM/FFM ratio and regional SM distributions are associated with the degree of absolute FFM accumulation in men and women.

The relation between local circulation and alternate muscle activity among knee extensor synergists was determined during low-level sustained knee extension at 2.5% of maximal voluntary contraction for 60 min in seven subjects. Blood volume of rectus femoris (RF) and vastus lateralis (VL) was assessed by using near-infrared spectroscopy. Surface electromyogram (EMG) was recorded from RF, VL, and vastus medialis (VM). Alternate muscle activity was observed between RF and either VL or VM. Cross-correlation analysis was used to investigate the relation between blood volume and integrated EMG (iEMG) sequences throughout the task. One negative peak in the cross-correlation function was seen between the iEMG and blood volume with time lag of 30-60 s, indicating that muscle activity increases (or decreases) with the decrease (or increase) in local circulation with the corresponding time lag. Two cases in the emergence of alternate muscle activities, i.e., an increase in the EMG of RF accompanied by a decline of EMG in VL (case I) and vice versa (case II) were further analyzed. The time lag between iEMG and blood volume was longer in case I than that in case II. These results were statistically significant in the RF but not in the VL. It is concluded that even during low-level sustained contraction, local circulation is modulated by the alternate muscle activity of knee extensor synergists, and a negative correlation between the muscle activity and blood volume sequences was found in only RF but not in VL.

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.

Aim: The purposes of this study were to determine the age-related changes in the tendon-aponeurosis structures and to investigate the effects of low-load resistance training on the tendon-aponeurosis structures in middle-aged and elderly women.
Methods: Fifty-one women (55.8 +/- 13.7 years, range: 21-77 years) volunteered to take part in the present study. Furthermore, 11 middle-aged and elderly women (49.7 +/- 9.2 years) performed the low-load resistance training, i.e. squat using body weight, for 6 months. The elongation of the tendon and aponeurosis of the vastus lateralis muscle was directly measured by ultrasonography, while the subjects performed ramp isometric knee extension up to the voluntary maximum, followed by a ramp relaxation. The relationship between the estimated muscle force (F (m) ) and tendon elongation (L ) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the F (m) -L loop to the area beneath the curve during the ascending phase was calculated as hysteresis.
Results: Maximal strain (L /initial tendon length) and stiffness of the tendon-aponeurosis structures decreased significantly with ageing. In contrast, the hysteresis increased significantly with ageing. In addition, low-load resistance training produced no significant change in stiffness and hysteresis, but significantly increased the maximal elongation of tendon-aponeurosis structures from 23.3 +/- 2.1 mm to 24.8 +/- 2.2 mm (P = 0.045).
Conclusion: These results suggest that increasing age results in a decrease in the elasticity of tendon-aponeurosis structures and an increase in their viscosity. Furthermore, the low-load resistance training made the elasticity of tendon-aponeurosis structures increase.

Isometric torque and the cross-sectional area (CSA) of the quadriceps femoris muscle (QF) were measured twice at an interval of 18 months in seven junior Olympic weight lifters (aged 15.5-17.1 years at the start of the study) to investigate the growth trend of this muscle group in junior athletes specializing in strength and power events. The CSAs of the QF and its four constituent muscles were determined at 30% (proximal to the knee), 50%, and 70% of femur length (F1) using a magnetic resonance imaging method. Only at 30% F1 were significant increases found in the CSAs of the QF and all constituent muscles, except for the rectus femoris. At this level, the CSA of the vastus medialis relative to the QF decreased significantly, suggesting a predominant hypertrophy in the vastus intermedius and vastus lateralis muscles. Isometric torque during knee extension increased significantly compared, to the CSA for the QF measured at the three levels. Thus, the present results indicate that, at least at high school age, the QF for junior Olympic weight lifters is characterized by a preferential hypertrophy at the level proximal to the knee joint, with an increase in knee extension torque relative to the CSA.

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 aim of the present study was to determine the transverse strain of aponeuroses in human tibialis anterior muscle (TA) in vivo and to clarify the influence of muscle fiber length and state of contraction on the transverse strain. Sagittal and horizontal images of TA were taken in seven men and one woman at ankle angles of -20degrees (dorsiflexed direction), 0degrees (neutral anatomic position), and 45degrees (plantar-flexed direction) both at rest and during submaximal dorsiflexion contraction (20 Nm: 0degrees and 45degrees; 10 Nm: -20degrees) using B-mode ultrasonography. The width of the TA central aponeurosis changed from 21.7 +/- 1.0 (mean +/- SE) to 25.5 +/- 1.1 mm when muscle fiber length changed from 91.0 +/- 3.5 (45degrees in the resting state) to 55.1 +/- 3.2 mm (-20degrees in the active state). The transverse strain of the TA central aponeurosis, which was change in relative width compared with the width at 45degrees in the resting state, increased when the muscle fiber length decreased. The transverse strain of the TA central aponeurosis was directly proportional to the muscle fiber length to the -1/2 power in both resting and active states (R = 0.81 and 0.74, p &lt; 0.05 for both), and there was no significant difference (p &lt; 0.05) between correlation coefficients and regression slopes for resting and active states. The findings suggest that the transverse strain of the TA central aponeurosis was closely related to muscle fiber length and that the transverse strain of the aponeurosis should be considered for accurate 3-D muscle modeling.

The purpose of this study was to investigate the differences in the viscoelastic properties of human tendon structures (tendon and aponeurosis) in the medial gastrocnemius muscle between men (n = 16) and women (n = 13). The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle was measured directly by ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) and tendon elongation (L) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness. The percentage of the area within the Fm-L loop to the area beneath the curve during the ascending phase was calculated as hysteresis. The L values at force production levels beyond 50 N were significantly greater for women than for men. The maximum strain (100xDeltaL/initial tendon length) was significantly greater in women [9.5 (1.1)%] than in men [8.1 (1.6)%]. The stiffness and Young's modulus were significantly lower in women [16.5 (3.4) N/mm, 277 (25) MPa] than in men [25.9 (7.0) N/mm, 356 (32) MPa]. Furthermore, the hysteresis was significantly lower in women [11.1 (5.9)%] than in men [18.7 (8.5)%, P = 0.048]. These results suggest that there are gender differences in the viscoelastic properties of tendon structures and that these might in part account for previously observed performance differences between the genders.

The purpose of this study was to compare the muscle architectural characteristics, i.e., muscle thickness, pennation angle, fascicle length, of four different groups comprising a total of 121 men and 190 women, divided according to sex and age (i.e., 20-39 yrs and 60-85 yrs). Muscle thickness and pennation angles of the vastus lateralis (VL), medial gastrocnemius (MG), long head of triceps brachii (TB) muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Men had significantly greater relative muscle thickness (to limb length) than women, but not for MG. Relative muscle thickness of VL was significantly greater in younger subjects than in elderly (men; p &lt; 0.001, women; p &lt; 0.001), although there were no significant differences in relative muscle thickness of MG and TB between younger and elderly subjects. Men had significantly greater pennation angles than women, but not for MG in elderly subjects. The pennation angle of VL was significantly greater in younger subjects than in elderly (men; p &lt; 0.001, women; p &lt; 0.001), although there were no significant differences in pennation angles of MG and TB between younger and elderly subjects. Women had longer relative fascicle lengths (to limb length) of VL than men (p = 0.048 for younger, p = 0.028 for elderly). These results suggest that the decrease of thickness of the vastus lateralis muscle with aging is significant, and that there is the gender difference in the fascicle length of the vastus lateralis muscle.

The influences of age on muscle architectural characteristics, i. e., muscle thickness, pennation angle, fascicle length, were studied in 121 men and 229 women aged 17 to 85 yrs. The subjects were divided into three age groups (younger : 17-39 yrs, middle-aged : 40-59 yrs, elderly : 60-85 yrs) for both genders. Muscle thickness and pennation angle of the vastus lateralis (VL), medial gastrocnemius (MG), and long head of triceps brachii (TB) muscles were measured using B-mode ultraso-nography, and fascicle length was estimated. In all age groups, men had significantly greater relative muscle thickness (to limb length) in VI, and TB than women, but not in MG. Relative muscle thickness of VL was significantly lower in elderly than in younger and middle-aged subjects. Ilowever, the corresponding differences in MG and TB were insignificant. The pennation angle of VL was significantly lower in elderly than in younger and middle-aged subjects, although there were no significant differences in pennation angles of MG and TB among the three groups. These results suggest that the decrease in thickness of vastus lateralis muscle with aging is significant, but not significant for medial gastrocnemius and triceps hrachii muscles.

Purpose: The purpose of this study was to investigate the muscle architectural characteristics, i.e., muscle thickness, pennation angle, and fascicle length, in women aged 20-79 yr. Methods: A total of 224 sedentary healthy women participated in this study. Muscle thickness and pennation angle of the vastus lateralis (VL), medial gastrocnemius (MG), and triceps brachii (TB) muscles were measured by B-mode ultrasonography, and the fascicle length was estimated. Results: Relative muscle thickness of VL and MG decreased significantly with advanced age (VL: P &lt; 0.01, MG: P &lt; 0.05). In addition, the ratio of muscle thickness of VL to that of MG decreased significantly with advanced age (r = -0.206, P &lt; 0.05). The pennation angle decreased significantly with aging for VL (P &lt; 0.001) but not for MG. For TB, no significant age-related changes in relative muscle thickness or pennation angle were observed. There were no significant correlations between age and relative fascicle length (to limb length) in any of the studied muscles. Conclusion: These results suggested that the declines in muscle thickness and pennation angle with aging were remarkable in the vastus lateralis muscle and slight in the medial gastrocnemius muscle. For the triceps brachii muscle, the muscle thickness and pennation angle did not decrease with advanced age. Furthermore, no significant age-related changes in relative fascicle length (to limb length) were observed in any of the studied muscles.

To determine quantitatively the features of alternate muscle activity between knee extensor synergists during low-level prolonged contraction, a surface electromyogram (EMG) was recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) in 11 subjects during isometric knee extension exercise at 2.5% of maximal voluntary contraction (MVC) for 60 min (experiment 1). Furthermore, to examine the relation between alternate muscle activity and contraction levels, six of the subjects also performed sustained knee extension at 5.0, 7.5, and 10.0% of MVC (experiment 2). Alternate muscle activity among the three muscles was assessed by quantitative analysis on the basis of the rate of integrated EMG sequences. In experiment 1, the number of alternations was significantly higher between RF and either VL or VM than between VL and VM. Moreover, the frequency of alternate muscle activity increased with time. In experiment 2, alternating muscle activity was found during contractions at 2.5 and 5.0% of MVC, although not at 7.5 and 10.0% of MVC, and the number of alternations was higher at 2.5 than at 5.0% of MVC. Thus the findings of the present study demonstrated that alternate muscle activity in the quadriceps muscle 1) appears only between biarticular RF muscle and monoarticular vasti muscles (VL and VM), and its frequency of alternations progressively increases with time, and 2) emerges under sustained contraction with force production levels less than or equal to5.0% of MVC.

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.

This study compared the effects of static stretching (ST) and repeated muscle contractions (CON) on the viscoelastic properties of tendon structures in vivo . Eight male subjects performed ST (passively flexed to 35 of dorsiflexion) for 5 min and 50 repetitions of isometric maximum voluntary contraction (MVC) for 3 s each with 3 s relaxation. Before and after each task, the elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured by ultrasonography, while the subjects performed ramp isometric plantar flexion up to MVC, followed by a ramp relaxation. The relationship between the estimated muscle force (F (m) ) and tendon elongation (L ) during the ascending phase was applied to a linear regression, the slope of which was defined as stiffness of the tendon structures. The percentage of the area within the F (m) -L loop to the area beneath the curve during the ascending phase was calculated as an index representing hysteresis. The ST protocol significantly decreased the stiffness (-8%) and hysteresis (29%)., respectively. In contrast, the CON protocol significantly decreased the stiffness, but not the hysteresis. These results suggested that the stretching and repeated contractions would make the tendon structures more complaint, and further decreased the hysteresis of the tendon structures.

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.

The purpose of this study was to investigate whether or not the neuromuscular locomotor system is optimized at a unique speed by examining the variability of the ground reaction force (GRF) pattern during walking in relation to different constant speeds. Ten healthy male subjects were required to walk on a treadmill at 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 km/h. Three components [vertical (F-x), anteroposterior (F-y), and mediolateral (F-x) force] of the GRF were independently measured for similar to35 steps consecutively for each leg. To quantify the GRIP pattern, five indexes (first and second peaks of F-z, first and second peaks of F-y, and F-x peak) were defined. Coefficients of variation were calculated for these five indexes to evaluate the GRF variability for each walking speed. It became clear for first and second peaks of F-z and F-x peak that index variabilities increased in relation to increments in walking speed, whereas there was a speed (5.5-5.8 km/h) at which variability was minimum for first and second peaks of F-y, which were related to forward propulsion of the body. These results suggest that there is "an optimum speed" for the neuromuscular locomotor system but only for the propulsion control mechanism.

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.

Load-strain characteristics of distal (deep) and proximal (superficial) aponeuroses were determined in vivo for human tibialis anterior muscle (TA). Seven male subjects exerted isometric dorsiflexion torque from relaxation to voluntary maximum while elongation of both aponeuroses of TA was determined by ultrasonography. Two positions (end of the muscle belly and a proximal part) and one position (distal part) were scanned for the deep and superficial aponeuroses, respectively, and tendinous movements of the respective positions were determined. Based on the tendinous movements, elongation of each aponeurosis was determined. Both aponeuroses were elongated significantly, and there was no significant difference in strain between the deep (3.3 +/- 0.8%) and superficial (3.0 +/- 0.5%) aponeuroses. In addition, there was a significant linear relationship between strain of deep and superficial aponeuroses. It was suggested that both aponeuroses similarly act as an elastic component in pennate muscles. Copyright (C) 2002 S. Karger AG, Basel.

This study aimed to investigate the suitability of using ultrasonograph muscle thickness (MT) measurements to estimate the muscle volume (MV) of the quadriceps femoris as an alternative approach to magnetic resonance imaging (MRI). The subjects were 46 men aged from 20 to 70 years who were randomly allocated to either a validation or a cross-validation group, In the validation group, multiple and simple regression equations, which used a set of MT values determined at mid-thigh and thigh length (1) and the product of pi. (MT/2)(2). and 1 [pi.(MT/2)(2).1]. respectively, as independent variables, were derived to estimate the MV measured by MRI. Because the two equations were cross-validated, the data from the two groups were pooled to generate the final prediction equations: MV (cm(3))=(MT x 311.732)+(1 x 53,346) -2058.529 as the multiple regression equation and MV (cm(3)) = [pi.(MT/ 2)(2).1] x 1.1176 663.040 as the simple regression equation. In the multiple regression equation, NIT explained 75% of the variation in the MV measured by MRI. The r(2) and the standard error of the estimate (SEE) of the equations were 0.824 and 175.6 cm(3) (10.6%), respectively. for the multiple regression equation and 0.829 and 173.7 cm(3) (10.5%), respectively, for the simple regression equation. Thus. the present results indicate that ultrasonograph NIT measurements at mid-thigh are useful for estimating the MV of knee extensors. However, the observed SEE values suggest that the prediction equation obtained in this study may be limited to population studies rather than individual assessments in longitudinal studies.

The purpose of this study was to examine whether stretching training altered the viscoelastic properties of human tendon structures in vivo. Eight men performed the stretching training for 3 wk. Before and after the stretching training, the elongation of the tendon and aponeurosis of medial gastrocnemius muscle was directly measured by ultrasonography while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between the estimated muscle force (Fm) and tendon elongation (L) during the ascending phase was fitted to a linear regression, the slope of which was defined as stiffness of tendon structures. The percentage of the area within the Fm-L loop to the area beneath the curve during ascending phase was calculated as an index representing hysteresis. To assess the flexibility, the passive torque of the plantar flexor muscles was measured during the passive stretch from 0° (anatomic position) to 25° of dorsiflexion with a constant velocity of 5°/s. The slope of the linear portion of the passive torque-angle curve during stretching was defined as flexibility index. Flexibility index decreased significantly after stretching training (-13.4 ± 4.6%). On the other hand, the stretching training produced no significant change in stiffness but significantly decreased hysteresis from 19.9 ± 11.7 to 12.5 ± 9.5%. The present results suggested that stretching training affected the viscosity of tendon structures but not the elasticity.

The present study examined whether resistance and stretching training programmes altered the viscoelastic properties of human tendon structures in vivo. Eight subjects completed 8 weeks (4 days per week) of resistance training which consisted of unilateral plantar flexion at 70% of one repetition maximum with 10 repetitions per set (5 sets per day). They performed resistance training (RT) on one side and resistance training and static stretching training (RST; 10 min per day, 7 days per week) on the other side. Before and after training, the elongation of the tendon structures in the medial gastrocnemius muscle was directly measured using ultrasonography, while the subjects performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between estimated muscle force (F-m) and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness. The hysteresis was calculated as the ratio of the area within the F-m-L loop to the area beneath the load portion of the curve. The stiffness increased significantly by 18.8 +/- 10.4% for RT and 15.3 +/- 9.3% for RST. There was no significant difference in the relative increase of stiffness between RT and RST. The hysteresis, on the other hand, decreased 17 +/- 20% for RST, but was unchanged for RT. These results suggested that the resistance training increased the stiffness of tendon structures as well as muscle strength and size, and the stretching training affected the viscosity of tendon structures but not the elasticity.

The effects of the local blood circulation and absolute torque on muscle endurance at different knee-joint angles were determined. The rate of muscle deoxygenation (using near-infrared spectroscopy), and the rate of muscle fatigue (using the slope of integrated electromyography. iEMG) were evaluated concurrently. Nine healthy subjects performed submaximal (50% maximal voluntary contraction. MVC) static knee extension at 50 degrees (extended position, EXT) and 90 degrees (flexed position, FLEX) joint angles until the target torque could no longer be maintained: that time was measured as the endurance time. They exercised with the circulation occluded (OCCL), and without (FREE) to study the possible effects of the local circulation. Although MVC torque was independent of joint angle [mean (SID) FLEX 250.6 (51.7) N(.)m and EXT 246.5 (46.6) N(.)m], significantly shorter (P &lt; 0.01) endurance time in FLEX [FREE 71.1 (10) s and OCCL 63.1 (8.8) s] than at EXT [FREE 115.3 (30) s and OCCL 106.7 (29.1) s] were obtained in both circulatory conditions. The iEMG-time slope was significantly greater in FLEX at the proximal and distal portion (P &lt; 0.05) in both circulatory conditions. Muscle deoxygenation rate in OCCL was significantly greater (P &lt; 0.05) at FLEX [20.8 (8.0)%] than EXT [10.9 (4.0)%]. The results would suggest that different knee-joint angle affects muscle endurance even if the local circulation is controlled. Circulatory disturbance would further reduce muscle endurance in EXT, but not in FLEX. Because of the greater muscle internal force in FLEX. local blood flow might be already limited even with a free circulation. The greater muscle deoxygenation and muscle fatigability would be related to the shorter muscle endurance in FLEX.

Aponeurotic deformation measurements have traditionally been taken by loading dissected muscles; thus the values obtained may not reflect in vivo function. In the present study, we estimated dimensional changes in the central aponeurosis of the intact human tibialis anterior muscle upon loading induced by muscle contraction. Measurements were taken in seven males, and involved real-time ultrasound scanning of the tibialis anterior muscle at 30 degrees of plantarflexion at rest and during isometric dorsiflexion maximum voluntary contraction (MVC). At each contraction state, the length of the aponeurosis, the width along its length, and its area were estimated from sagittal-plane and axial-plane sonographs. In the transition from rest to MVC, the length of the aponeurosis increased by 7% (P &lt; 0.05), its width increased by up to 21% (P &lt; 0.05), and its area increased by 17% (P &lt; 0.05). These results indicate that the in vivo tibialis anterior aponeurosis behaves as a compliant material upon active muscle shortening. The methodology employed allows cross-sectional and longitudinal design investigations, circumventing the problems associated with epimysial removal under in vitro experimental conditions.

1. The present study aimed to investigate the influence of isometric training protocols with long- and short-duration contractions on the elasticity of human tendon structures in vivo. The elasticity was assessed through in vivo determination of the elongation (L) of the tendons and aponeuroses using ultrasonography, while the subjects performed ramp isometric exercise up to maximum voluntary contraction (MVC).
2. Eight young males completed 12 weeks (4 days per week) of a unilateral isometric training programme on knee extensors, which consisted of two different combinations of contraction and relaxation times at 70% MVC: one leg was trained using a short-duration protocol (3 sets of 50 repetitions of contraction for I s and relaxation for 2 s), and the other leg was trained using a long-duration protocol (4 sets of a combination of contraction for 20 s and relaxation for I min). The training volume per session, expressed as the integrated torque, was the same for the two protocols.
3. Both protocols resulted in a significant increase in MVC: 31.8 +/- 17.2% for the short-duration protocol and 33.9 +/- 14.4% for the long-duration protocol. Moreover, the training produced significant increases in the muscle volume of the constituents of the quadriceps femoris, with similar relative gains for the two protocols: 7.4 +/- 3.9% for the short-duration protocol and 7.6 +/- 4.3% for the long-duration protocol.
4. The short-duration protocol produced no significant change in L values at any of the force production levels. For the long-duration protocol, however, the L values above 550 N were significantly shorter after training, Analysis revealed that the group x test time interaction effect on tendon stiffness was significant. Stiffness increased significantly for the long-duration protocol, but not for the short-duration protocol.
5. The present study demonstrates a greater increase in stiffness of human tendon structures following isometric training using longer duration contractions compared to shorter contractions. This suggests that the changes in the elasticity of the tendon structures after resistance training may be affected by the duration of muscle contraction.

We evaluated the stretch reflex activities of the elbow flexor and extensor muscles considering the relationship between the reflex electromyographic (EMG) responses and their corresponding standardized muscle stretch velocities. Specifically, muscular stretch velocity was estimated by using ultrasonograms. Stretch reflex EMG responses were elicited in the biceps brachii, brachioradialis and triceps brachii with a ramp-and-hold rotation at the elbow joint, which consisted of various angular velocities for the extension- or flexion-direction. The whole muscle stretch velocity induced by each ramp-and-hold rotation was calculated on the basis of fibre length changes associated with the elbow joint angle. A linear regression equation was fitted to the relation between the whole muscle stretch velocity and the reflex EMG responses, and the variables from the equation were used to quantify sensitivity of each reflex EMG component. The reflex EMG responses were increased as the ramp-and-hold rotational velocity increased. There were no significant differences in the recorded magnitudes of reflex EMG responses with equivalent joint rotational velocity between the brachioradialis and the triceps brachii medial head. These muscles showed the highest reflex responses in the flexor and extensor muscles, respectively. To the contrary, the reflex EMG response elicited by the standardized muscle stretches was significantly greater in the extensor muscles, indicating a higher reflex sensitivity. This was because of the lower muscle stretch velocity of the triceps brachii with an equivalent elbow joint rotation. The stretch reflex sensitivity in both the elbow flexor and extensor muscles might be regulated so as to make the reflex responses the same when the equivalent joint rotational velocity is applied to these muscles.

The purpose of this study was to examine in vivo whether passive stiffness in human muscles was related to the elasticity of tendon structures and to performance during stretch-shortening cycle exercise. Passive torque of plantar flexor muscles was measured during passive stretch from 90 degrees (anatomical position) to 65 degrees of dorsiflexion at a constant velocity of 5 degrees .s(-1). The slope of the linear portion of the passive torque-angle curve during stretching was defined as the passive stiffness of the muscle. The elongation of the tendon and aponeurosis of the medial gastrocnemius muscle (MG) was directly measured using ultrasonography during ramp isometric plantar flexion up to the voluntary maximum. The relationship between the estimated muscle force of MG and tendon elongation was fitted to a linear regression, the slope of which was defined as the stiffness of the tendon. In addition, the dynamic torques during maximal voluntary concentric plantar flexion with and without prior eccentric contraction were determined at a constant velocity of 120 degrees .s(-1). There were no significant correlations between passive stiffness and either the tendon stiffness (r=0.19, P&gt;0.05) or the relative increase in torque with prior eccentric contraction (r=-0.19, P&gt;0.05). However, tendon stiffness was negatively correlated to the relative increase in torque output (r=-0.42, P&lt;0.05). The present results suggested that passive stiffness was independent of the elasticity of tendon structures, and had no favourable effect on the muscle performance during stretch-shortening cycle exercise.

Muscle force (MF) is linearly related to physiological cross-sectional area (CSA), which is obtained from muscle volume (MV) divided by fibre length. Taking into account the fact that joint torque (TO) is determined by MF multiplied by the moment arm, the maximal TO would be a function of MV. This proposition was tested in the present study by investigating the relationship between MV and TO for elbow flexor (EF) and extensor (EE) muscles of 26 males. The MVs of EF and EE were determined from a series of muscle CSA by magnetic resonance imaging (MRI), and pennation angle (theta) and FL by ultrasonography (US). Maximal isometric TO was measured at right angle of elbow joint for EF and EE, There was a highly significant correlation between MV and TO both for EF and EE (r = 0.95 and 0.96 respectively) compared with that between muscle CSA and TO, suggesting the dependence of TO on MV. Furthermore, prediction equations for MV (MVULT) from muscle thickness (MT) measured by US was developed with reference to MVMRI, by the MRI on 26 subjects, and the equations were applied to estimate MV of healthy university students (CON; 160 males) and sports athletes (ATH; 99 males), There were significant linear relationships between MVULT and TO both for EF (r = 0.783) and EE (r = 0.695) for all subjects (n = 259). The MVULT was significantly higher in ATH (by 32% for EF and 33% for EE, respectively) than in CON. Similarly, significantly greater TO was observed in ATH (by 35% for EF, 37% for EE, respectively). The theta for EE showed no difference between both groups (17.8 degrees for CON and 17.5 degrees for ATH). On the other hand, the TO to MV ratio were identical for CON and ATH. The results reveal that the muscle volume of the upper arm is a major determinant of joint torque (TQ), regardless of athletic training.

The present study aimed to investigate the effect of dynamic leg press training on the physiological cross-sectional areas (PCSAs) of human lower limb muscles during 20 days of 6 degrees head-down tilt bed rest. Five healthy men comprised the resistance training group (BR-Tr) and data from two previous studies were used to derive a 10-man control group (BR-Cont). The BR-Tr performed two sessions (morning and afternoon session) of dynamic leg press action including knee extension and plantar flexion daily for the bed rest period: (1) three sets of 10 repetitions at 90% of maximum load and (2) 40% of maximum load to exhaustion. The PCSAs of the knee extensor (KE), knee flexor (KF), plantar flexor (PF), and dorsiflexor muscle groups were estimated using serial axial magnetic resonance (MR) images of the right-thigh and leg. After the bed rest period, the BR-Tr showed a significant increase in the PCSA of the KE. Although PCSA of the KF in two groups significantly decreased after bed rest, percentage of change in PCSA of the biceps femoris (long head) and semitendinosus muscles in the BR-Tr, which occupied approximately 70% of the KF, was significantly higher than those in the BR-Cont. Both the BR-Tr and BR-Cont groups showed significant decreases in the PCSA of PF with similar magnitude of 11.6% (P &lt; 0.001) and 11.9% (P &lt; 0.001), respectively. These results suggest that dynamic leg press training during bed rest can prevent deteriorating of the KE and a part of KF, but not the calf muscles.

The present study aimed to investigate the validity of estimating muscle volume by bioelectrical impedance analysis. Bioelectrical impedance and series cross-sectional images of the forearm, upper arm, lower leg, and thigh on the right side were determined in 22 healthy young adult men using a specially designed bioelectrical impedance acquisition system and magnetic resonance imaging (MRI) method, respectively. The impedance index (L-2/Z) for every segment, calculated as the ratio of segment length squared to the impedance, was significantly correlated to the muscle volume measured by MRI, with r = 0.902-0.976 (P &lt; 0.05). In these relationships, the SE of estimation was 38.4 cm(3) for the forearm, 40.9 cm(3) for the upper arm, 107.2 cm(3) for the lower leg, and 362.3 cm(3) for the thigh. Moreover, isometric torque developed in elbow flexion or extension and knee flexion or extension was significantly correlated to the L-2/Z values of the upper arm and thigh, respectively, with correlation coefficients of 0.770-0.937 (P &lt; 0.05), which differed insignificantly from those (0.799-0.958; P &lt; 0.05) in the corresponding relationships with the muscle volume measured by MRI of elbow flexors or extensors and knee flexors or extensors. Thus the present study indicates that bioelectrical impedance analysis may be useful to predict the muscle volume and to investigate possible relations between muscle size and strength capability in a limited segment of the upper and lower limbs.

The present study aimed to investigate the effect of isometric training on the elasticity of human tendon structures. Eight subjects completed 12 wk (4 days/wk) of isometric training that consisted of unilateral knee extension at 70% of maximal voluntary contraction (MVC) for 20 s per set (4 sets/day). Before and after training, the elongation of the tendon structures in the vastus lateralis muscle was directly measured using ultrasonography while the subjects performed ramp isometric knee extension up to MVC. The relationship between the estimated muscle force and tendon elongation (L) was fitted to a linear regression, the slope of which was defined as stiffness of the tendon structures. The training increased significantly the volume (7.6 +/- 4.3%) and MVC torque (33.9 +/- 14.4%) of quadriceps femoris muscle. The L values at force production levels beyond 550 N were significantly shorter after training. The stiffness increased significantly from 67.5 +/- 21.3 to 106.2 +/- 33.4 N/mm. Furthermore, the training significantly increased the rate of torque development (35.8 +/- 20.4%) and decreased electromechanical delay (-18.4 +/- 3.8%). Thus the present results indicate that isometric training increases the stiffness and Young's modulus of human tendon structures as well as muscle strength and size. This change in the tendon structures would be assumed to be an advantage for increasing the rate of torque development and shortening the electromechanical delay.

The present study aimed to investigate the effects of repetitive muscle contractions on the elasticity of human tendon structures in vivo. Before and after each endurance test, the elongation of the tendon and aponeurosis of vastus lateralis muscle (L) was directly measured by ultrasonography while the subjects performed ramp isometric knee extension up to maximal voluntary isometric contraction (MVC). Six male subjects performed muscle endurance tests that consisted of knee extension tasks with four different contraction modes: 1) 50 repetitions of maximal voluntary eccentric action for 3 s with 3 s of relaxation (ET1), 2) three sets of 50 repetitions of MVC for 1 s with 3 s of relaxation (ET2), 3) 50 repetitions of MVC for 3 s with 3 s of relaxation (ET3), and 4) 50 repetitions of 50% MVC for 6 s with 6 s of relaxation (ET4). In ET1 and ET2, there were no significant differences in L values at any force production levels between before and after endurance tests. In the cases of ET3 and ET4, however, the extent of elongation after the completion of the tests tended to be greater. The L values above 330 N in ET3 and 440 N in ET4, respectively, were significantly greater after endurance tests than before. These results suggested that the repeated longer duration contractions would make the tendon structures more compliant and that the changes in the elasticity might be not be affected by either muscle action mode or force production level but by the duration of action.

Load-strain characteristics of tendinous tissues (Achilles tendon and aponeurosis) were determined in vivo for human medial gastrocnemius (MG) muscle. Seven male subjects exerted isometric plantar flexion torque while the elongation of tendinous tissues of MG was determined from the tendinous movements by using ultrasonography. The maximal strain of the Achilles tendon and aponeurosis, estimated separately from the elongation data, was 5.1 +/- 1.1 and 5.9 +/- 1.6%, respectively. There was no significant difference in strain between the Achilles tendon and aponeurosis. In addition, no significant difference in strain was observed between the proximal and distal regions of the aponeurosis. The results indicate that tendinous tissues of the MG are homogenously stretched along their lengths by muscle contraction, which has functional implications for the operation of the human MG muscle-tendon unit in vivo.

Behavior of fascicles and tendinous structures of human gastrocnemius medialis (MG) was determined by use of ultrasonography in vivo during jumping. Eight male subjects jumped vertically without countermovement (squat jump, SQJ). Simultaneously, kinematics, kinetics, and electromyography from lower leg muscles were recorded during SQJ. During phase 1 (-350 to -100 ms before toe-off, muscle-tendon complex (MTC) length was almost constant. Fascicles, however, shortened by 26%, and tendinous structures were stretched by 6%, storing elastic energy of 4.9 J during phase I. During phase II(-100 ms to toe-off), although fascicles generated force quasi-isometrically, MTC shortened rapidly by 5.3%, releasing prestored elastic energy with a higher peak positive power than that of fascicles. Also, the compliance of tendinous structures in vivo was somewhat higher than that of external tendon used in the simulation studies. The results demonstrate that the compliance of tendinous structures, together with no yielding of muscle fibers, allows MTC to effectively generate relatively large power at a high joint angular velocity region during the last part of push-off.

Background. The present study aimed to investigate the gender- and age-related profiles of junior speed skaters in strength capabilities during both single and repetitive maximal contractions.
Methods. The subjects were 19 male (age= 17.1+/-0.2 years, X+/-SE) and 13 female skaters (16.9+/-0.2 years). Isokinetic knee extension torque (T) developed concentrically in a single contraction at three constant velocities of 1.05, 3.14 and 5.24 rad/sec and 50 repetitive maximal contractions at 3.14 rad/sec was measured using an isokinetic dynamometer, in addition, a B-mode ultrasound apparatus was used to determine the cross-sectional area (CSA) of the quadriceps femoris muscle at mid-thigh.
Results, For the junior skaters, T values at three velocities of 1.05, 3.14 and 5.24 rad/sec and the mean value of isokinetic torque (MT) for every five consecutive trials in the first 25 maximal contractions were similar in both genders when they were expressed relative to the product of the cross-sectional area (CSA) of the quadriceps femoris muscle and lower limb Length, T/CSAL and MT/CSAL, respectively. However, the males showed significantly higher MT/CSAL values than the females in the last 25 repetitions of the endurance test. In the comparisons between junior and reference senior skaters, T/CSAL for both genders and MT/CSAL for the females showed little age-related difference, For the males, however, MT/CSAL values in the first 15 repetitions of the endurance test were significantly lower in the junior skaters than in the senior ones,
Conclusions, The present results indicate that the strength capabilities of junior speed skaters in a single maximal contraction will be similar in both genders when the difference in muscle size is normalized. However, the junior male skaters may be less fatiguable than the junior female ones in repetitive maximal contractions. Moreover, the comparison between junior and senior skaters suggests that, in postadolescence, males might be more trainable than females to improve torque output during short-term repetitive maximal contractions beyond that achieved during adolescence.

An evaluation of mechanical power during walking and running in humans was undertaken after developing a specially designed running ergometer (RE) in which the subjects gripped the handlebar in front of them keeping both arms straight and in a horizontal position. Ten subjects participated in comparisons of the mean horizontal pushing force (MFam) on the handlebar with the mean horizontal ground reaction force (MFfp) recorded by force platform under the RE during five different constant speeds of walking or running and sprint running with maximal effort. Mechanical power developed during sprint running on the RE was compared with a 50 m sprint. Mean linear velocity (M nu) of the RE belt was recorded by the rotary encoder attached to the axis of the belt. Mean mechanical power calculated from the handlebar setting (MPam = MFam x M nu) was compared to that calculated from force platform recordings (MPfp = MFfp x M nu). A high test-retest reproducibility was observed for both MFfp (r = 0.889) and MFam (r = 0.783). Larger values for the coefficient of variation for MFam (11.3%-15.8%) were observed than for MFfp (3.3%-8.2%). The MPam, which were obtained from five different constant speeds of walking, running and sprint running were closely correlated to those of MPfp (y = 0.98x - 19.10, r = 0.982, P &lt; 0.001). In sprint running, MPam was 521.7 W (7.67 W (.) kg(-1)) and was correlated to the 50 m sprint time (r = -0.683, P &lt; 0.01). It is concluded that the newly developed RE was useful in the estimation of mechanical power output during human locomotion such as when walking, jogging and sprinting.

The purpose of this study was to investigate the growth changes in the elastic properties of human tendon structures. 9 younger boys (age 10.8 +/- 0.9 years, YBG), 9 elder boys (14.8 +/- 0.3 years, EBG), and 14 young adult men (24.7 +/- 1.6 years, ADG) volunteered to take part in the present study. Using a B-mode ultrasonic apparatus, the elongation of tendon and aponeurosis of vastus lateralis muscle (VL) was noninvasively measured in vivo, while subjects performed the extension of knee joint isometrically with force production levels from zero (relax) to maximal voluntary contraction (MVC) within 5 seconds. A curvilinear relationship was found between elongation of tendon structures (dL) and muscle force (Fm). This relationship consisted of two components, a steep initial change in length followed by a linear-region. The relationship between dL and Fm was fitted to a linear regression, and then the dL and dFm within 50 to 100% MVC was defined as compliance of tendon structures. The MVC force was the greatest in ADC and the lowest in YBG among the three groups. Significant age-related differences were found in compliance; 4.1 +/- 0.9(.)10(-2) mm/N for YBG, 2.9 +/- 1.1(.)10(-2) mm/N for EBG and 1.8 +/- 0.3(.)10(-2) mm/N for ADG. The dL/thigh length (TL) was significantly greater in YBG than in the other two groups above 0.35 MPa of Fm per muscle cross-sectional area (muscle stress). However, there was no significant difference between EBG and ADG in the relationship between dL/TL and muscle stress. The ratio of fascicle length to TL in YBG was significantly lower than those in the other two groups. These results suggest that the tendon structures in younger boys are more compliant than those in older boys and young men. The observed properties of tendon structures in the younger boys may play a role in protecting younger boys from athletic injuries associated with immature muscle-tendon complex.

In the present study we investigated in vivo length changes in the fascicles and tendon of the human gastrocnemius medialis (GM) muscle during walking. The experimental protocol involved real-time ultrasound scanning of the GM muscle, recording of the electrical activity of the muscle, measurement of knee- and ankle-joint rotations, and measurement of ground reaction forces in six men during walking at 3 km h(-1) on a treadmill. Fascicular lengths Were measured from the sonographs recorded, Musculotendon complex length changes were estimated from anatomical and joint kinematic data. Tendon length changes were obtained combining the musculotendon complex and fascicular length-change data. The fascicles followed a different length-change pattern from those of the musculotendon complex and tendon throughout, the step cycle. Two important features emerged: (i) the muscle contracted near-isometrically in the stance phase, with the fascicles operating at ca. 50 mm; and (ii) the tendon stretched by ca. 7 mm during single support and recoiled in push-off. The behaviour of the muscle in our experiment indicates consumption of minimal metabolic energy for eliciting the contractile forces required to support and displace the body On the other hand, the spring-like behaviour of the tendon indicates storage and release of elastic-strain energy. Either of the two mechanisms would favour locomotor economy.

Muscle fascicle lengths of vastus lateralis (VL) muscle were measured in five healthy men during slow pedaling to investigate the interaction between muscle fibers and tendon. Subjects cycled at a pedaling rate of 40 rpm (98 W). During exercise, fascicle lengths changed from 91 +/- 7 (SE) to 127 +/- 5 mm. It was suggested that fascicles were on the descending limb of their force-length relationship. The average shortening velocity of fascicle was greater than that of muscle-tendon complex in the first half of the knee extension phase and was less in the second half. The maximum shortening velocity of fascicle in the knee extension phase was less than that of muscle-tendon complex by 22 +/- 9%. These discrepancies in velocities were mainly caused by the elongation of the tendinous tissue. It was suggested that the elasticity of VL tendinous tissue enabled VL fascicles to develop force at closer length to their optimal length and kept the maximum shortening velocity of VL fascicles low during slow pedaling.

The purpose of this study was to investigate the changes in the elastic properties of tendons in humans in relation to fatigue of knee extensor muscles. The muscle fatigue test (MFT) consisted of maximal isometric contractions performed 50 times. The decline in peak moment was 43.6 (SD 19.5)%. After MFT, the muscle thickness and pennation angle of the vastus lateralis muscle (VL) significantly increased 1.5 (SD 0.7) mm (5%) and 1.7 (SD 1.8)degrees (11%), respectively. Before and after MFT, the elongation (I) of the tendon and aponeurosis of VL was directly measured by ultrasonography, while the subjects performed ramp isometric knee extensions up to maximal voluntary contraction. The I tended to be greater after MFT than before MFT. This difference in the I was statistically significant (P &lt; 0.05) at force developments beyond 220 N. Furthermore, the compliance increased significantly from 2.0 (SD 0.6) . 10(-2) mm . N-1 before MFT to 2.6 (SB 0.7) . 10(-2) mm . N-1 after MFT (22.7%). In addition, the electromechanical delay was significantly increased from 60.6 (SD 5.9)ms before to 70.0 (SD 4.4) ms after MFT. These results suggested that the repeated muscle contractions made the tendon structures more compliant.

Nine healthy men carried out head-down bed rest (BR) for 20 days. Five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [-10.9 (SD 6.9)%, P &lt; 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by -7.8 (SD 0.8)% (P &lt; 0.05) while in TR PCSA showed only an insignificant tendency to decrease [-3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.

The purpose of this study was to investigate the effects of 20 days bed-rest on the elastic properties of tendon structures of the human knee extensor muscles in vivo. Six healthy men carried out a 60 head-down bed-rest for 20 days. Muscle volume and maximal voluntary contraction (MVC) torque of the quadriceps femoris muscle significantly decreased by an average of 7.8 (SD 2.7)% and 14.9 (SD 6.9)%, respectively. Before and after bed-rest, the elongation (l) of the tendon and aponeurosis of vastus lateralis muscle was measured directly by ultrasonography, while the subjects performed ramp isometric knee extension up to MVC. The extent of l tended to be greater after bed-rest. The I above 110 N was significantly greater after bed-rest. Furthermore, the mean stiffness after bed-rest [35.5 (SD 7.8)N(.)mm(-1)] was significantly lower than that before bed-rest [52.6 (SD 19.2) N(.)mm(-1)]. The rate of torque development significantly reduced after bedrest by an average of 47%, and the bed-rest induced a lengthening in the electromechanical delay (mean 21%). These results suggest that bed-rest results in a decrease in the stiffness of tendon structures with a reduction of muscle strength and volume. These adaptations of the tendon structures to bed-rest would bring about the changes in electromechanical delay and rate of torque development.

Background. The purpose of this study was to investigate the profiles of muscle cross-sectional area (CSA) and strength capability in relation to lifting ability in Olympic weight lifters.
Methods. The subjects were 8 elite senior lifters (ESL, age=25.2+/-1.3 years, height=1.64+/-0.03 m, mass=68.6+/-4.2, kg, mean+/-SEM) and 9 college lifters (CL, 20.8+/-0.3 years, 1.67+/-0.03 m, 70.53.4 kg) whose predetermined weight classes were within the same range. The CSAs of elbow or knee extensor and elbow or knee flexor muscles were measured using a B-mode ultrasound apparatus. Concentric and eccentric maximal voluntary forces were determined with an isokinetic dynamometer at a constant velocity of 1.05 rad/sec.
Results. The best score of the total mass lifted in the snatch and the clean and jerk lifts was significantly higher in ESL than in CL even in terms of per unit of fat-free mass. There were no significant differences between the tno groups in fat-free mass, muscle CSA and force values with the exception that ESL compared to CL showed significantly greater force in concentric knee flexion. However, the ratios of force to muscle CSA (F/CSAs) in concentric and eccentric elbow extensions, eccentric knee extension and concentric knee flexion were significantly higher in ESL than in CL.
Conclusions. The present results indicated that the magnitude of muscular development in limbs was similar in elite senior and college lifters whose predetermined weight classes were within the same range. As compared to college lifters, however, elite senior lifters had a higher F/CSA in specific muscle action modes, which might relate to the optimal execution of the Olympic lifts.

The purpose of the present study was to investigate the effect of recruitment on the relationship between peak torque and physiological cross-sectional area (PCSA) in human muscle. A group of 11 healthy men participated in this study. Isokinetic knee extension torques at seven (0, 30, 60, 120, 180, 240, and 300 degrees (.)s(-1)) velocities were determined. Magnetic resonance imaging (MRI) was performed to calculate PCSA of right quadriceps femoris (QF) muscle. Exercise-induced contrast shifts in spin-spin relaxation time (T2)-weighted MRI were taken at rest and immediately after repetitive knee-extension exercise and T2 of QF were calculated. The MRI pixels with T2 values more than 1 SD greater than the means at rest were considered to represent QF muscle that had contracted. The area of activated PCSA within the total in QF was expressed as percentage activated PCSA and used as an index of muscle recruitment. The PCSA correlated with peak torque at 0 degrees (.)s(-1) (r = 0.615, P &lt; 0.05); in contrast, activated PCSA correlated with peak torque at 120&lt;degrees&gt;(.)s(-1) (r = 0.603, P &lt; 0.05) and 180&lt;degrees&gt;(.)s(-1) (r = 0.606, P &lt; 0.05). Additionally, there was a significant difference in correlation coefficients between the activated PCSA-peak torque relationship and the PCSA-torque relationship (P &lt; 0.05). These results suggested that muscle recruitment affects the PCSA-torque relationship.

We investigated the recruitment plasticity of the superficial tibialis anterior (TA-s) and deep tibialis anterior (TA-d) regions of neuromuscular compartments (NMCs) in the m. tibialis anterior (TA) during exercise using echo-planar imaging (EPI). Six healthy men performed dorsiflexion exercise at 60% of maximum voluntary contraction at a frequency of 10 contractions/min inside the magnetic resonance imaging. Transaxial EPIs of the right leg were acquired every 6 s at rest (0.5 min), during exercise (2.5 min) and recovery(5 min). In TA-s, significantly higher signal intensities (SIs) were shown than those in TA-d from immediately after starting the exercise to recovery. It has been demonstrated that SI reflects the degree of recruitment in the activated muscle, thus our result suggest that preferential firing of motor neurons in the superficial region of the NMC occurs during exercise in human TA muscle. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.

The purpose of this study was to investigate the dynamics of human muscle-tendon complex (MTC) during stretch-shortening cycle exercises through in vivo observation. A total of seven male subjects performed dorsi flexion followed by plantar flexion at two different frequencies, 0.3 Hz (slow) and 1.0 Hz (fast), in a toe-standing position. The fascicle length (L-F) of the medial gastrocnemius muscle during the movements was determined using a real-time ultrasonography in vivo. The L-F at the switching phase from dorsi to plantar flexion was significantly shorter in the fast exercise (54.4 +/- 5.5 mm) than in the slow one (58.2 +/- 5.4 mm), suggesting that the elongation of tendon structures at that time was significantly greater in the former than in the latter. Furthermore, at the initial stage of plantar flexion during the fast movement, the L-F hardly changed with a rapid shortening of tendon structures at that time. The observed relation between MTC length and force showed that the behaviour of tendon structures contributed to 20.2 and 42.5% of the total amount of work completed during plantar flexion phase in the slow and fast movements, respectively. Thus, the present results suggest that tendon structures make the dynamics of MTC more efficient during stretch-shortening cycle exercises by changing their lengths.

The purpose of the study was to examine the effect of prolonged tonic vibration applied to a single synergist muscle on maximal voluntary contraction (MVC) and maximal rate of force development (dF/dt(max)). The knee extension MVC force and surface electromyogram (EMG) from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) during MVC were recorded before and after vibration of RF muscle at 30 Hz for 30 min. MVC, dF/dt(max), and the integrated EMG (iEMG) of RF decreased significantly after prolonged tonic vibration in spite of no changes in iEMG of VL and VM. The present results indicate that MVC and dF/dt(max) may be influenced by the attenuated Ia afferent functions of a single synergist muscle.

The present study aimed to investigate the validity of bioelectrical impedance and ultrasonographic methods for predicting the muscle volume of the upper arm. Bioelectrical impedance of the right upper arm and the thickness of elbow flexor and extensor muscles were measured from 26 healthy young adult men using a specially designed bioelectrical impedance data acquisition system and brightness-mode ultrasound apparatus, respectively. As reference data, the muscle volume (MVMRI) of the right upper arm was determined using a magnetic resonance imaging method. The impedance index was calculated as L-2/Z, where L is the upper arm length and Z is the impedance of the shoulder to the elbow. The muscle volume (MVULT) was calculated as pi . (d/2)(2) . L, where d is muscle thickness. L-2/Z and MVULT were significantly correlated with MVMRI with correlation coefficients of 0.971 and 0.962, respectively. In these relationships, the standard errors of estimation were 44.2 cm(3) (6.3%) for L-2/Z and 50.7 cm(3) (7.2%) for MVULT. There was no significant difference between the absolute errors of muscle volumes estimated by L-2/Z and MVULT: 36.2 (4.8, SEM) cm(3) for L-2/Z versus 40.3 (5.8) cm for MVULT. The present results suggest that both bioelectrical impedance and ultrasonographic methods may be useful for predicting the muscle volume of the upper arm.

Isometric skeletal muscle fatigue is usually assumed to be a linear process based upon the monotonic decrease in spectral frequency of the EMG. Since spectral analysis by fast Fourier transform (FFT) constitutes a linear transformation of the data, the present study was designed to reevaluate the time-course of muscle fatigue with a nonlinear tool, recurrence quantification analysis (RQA). Surface EMG recordings were obtained from the multifidus muscle of 17 human subjects during isometric posture-holding of the upper torso. The process of muscle fatigue was found to be linear for 59% of the subjects by FFT criteria, but nonlinear for 76% by RQA criteria. As a demonstrative control, both slow and fast transients occurring within a nonlinear mathematical process could be accurately depicted by RQA, but not by FFT. It is concluded that assessment of EMG patterns by nonlinear techniques can give insight into the time-course of fatiguing muscles attributed to the summation of several nonlinear and competing processes.

The purpose of this study was to investigate the effects of resistance training on the morphological and functional properties of human lower limb muscles during 20 days of 6 degrees head-down-tilt bed rest. Nine men were randomly assigned to the resistance training group (BR-Tr, n = 5) or the non-training, control group (BR-Cont, n = 4). Isometric leg-press exercises were performed: 3 s x 30 repetitions (30 s rest between repetitions) daily for 20 days during the bed-rest period. Serial axial magnetic resonance images were taken from the right thigh and leg muscles, and muscle volume, muscle length, and fibre length were estimated. The physiological cross-sectional areas (PCSAs) of the knee extensor. knee flexor, ankle plantarflexor, and ankle dorsiflexor (tibialis anterior) muscle groups were determined as muscle volume multiplied by the cosine of the angle of fibre pennation divided by fibre length. Maximum voluntary contraction (MVC) during knee extension was measured. No significant changes were observed in the PCSA of the knee extensor muscles in BR-Tr group, whereas the PCSA in the BR-Cont group decreased by 7.8%. The PCSA of the knee flexor and plantarflexor muscles in the BR-Tr group and BR-Cont group significantly decreased after bed rest (knee flexors, 10.2% and 11.5%; plantarflexors, 13.0% and 12.8%, respectively). However, in both groups bed rest had no effect on the muscle volume and PCSA of the tibialis anterior. MVC was maintained by resistance training in the BR-Tr group (decreased by 1%). In contrast, a decline of strength was observed in the BR-Cont group (-16%), but this result was not statistically significant. These results suggest that isometric leg-press training prevents the deconditioning (i.e. atrophy and decline of strength) of the knee extensor muscle group.

To determine the shortening velocities of fascicles of the vastus lateralis muscle (VL) during isokinetic knee extension, six male subjects were requested to extend the knee with maximal effort at angular velocities of 30 and 150 degrees/s. By using an ultrasonic apparatus, longitudinal images of the VL were produced every 30 ms during knee extension, and the fascicle length and angle of pennation were obtained from these images. The shortening fascicle length with extension of the knee (from 98 to 13 degrees of knee angle; full extension = 0 degrees) was greater (43 mm) at 30 degrees/s than at 150 degrees/s (35 mm). Even when the angular velocity remained constant during the isokinetic range of motion, the fascicle velocity was found to change from 39 to 77 mm/s at 150 degrees/s and from 6 to 19 mm/s at 30 degrees/s. The force exerted by a fascicle changed with the length of the fascicle at changing angular velocities. The peak values of fascicle force and velocity were observed at similar to 90 mm of fascicle length. In conclusion, even if the angular velocity of knee extension is kept constant, the shortening velocity of a fascicle is dependent on the force applied to the muscle-tendon complex, and the phenomenon is considered to be caused mainly by the elongation of the elastic element (tendinous tissue).

The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%-100%, of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle Fat every 10% of MVC became almost constant. The maximal L (L-max) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for L-max and 1.55 (SD 0.25) x 10(-2) mm . N-1 in LDR compared to 1.88 (SD 0.82) x 10(-2) mm . N-1 in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (E-e) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with countermovement was significantly correlated to either MTC compliance (r = 0.554, P &lt; 0.05) or E-e (r = 0.563, P &lt; 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ.

The present study aims to investigate the elasticity of tendon structures of the lower limbs in sprinters and its relation with sprint performance. Subjects were 10 male sprinters and 14 controls whose anthropometric variables and isometric maximum strength were similar. The elongation iii of the tendon and aponeurosis of vastus lateralis (VL) and medial gastrocnemius muscles (MG) during isometric knee extension and planter flexion, respectively, were determined using a real-time ultrasonic apparatus in vivo, while the subjects developed a gradually increasing torque from zero (relax) to maximal effort (MVC) within 5 s. While sprinters compared with controls showed significantly greater L above 500 N (about 50% of MVC) and higher dL/dF for VL at less than 20% of MVC during knee extension, there were no significant differences between the two groups in L and dL/dF for MG at every 10% of MVC during planter flexion. Moreover, the average value of dL/dF above 50% of MVC, proposed as the compliance of tendon structures, did not significantly differ between sprinters and controls in either VL or MG. In a regression analysis within sprinters, the compliance of VL was negatively correlated to 100-m sprint time, r= -0.757 (P &lt; 0.05), but that of MG was not, r= 0.228 (P &gt; 0.05). Thus the present results indicate that the elasticity of tendon structures of VL and MG at high force production levels, which might be assumed to associate with the storage and subsequent release of energy during exercises involving the stretch-shortening cycle, are similar in both sprinters and controls. For sprinters, however, the tendon structures of VL are more compliant than that for controls at low force production levels, and its elasticity at high force production levels may influence sprint performance.

During human walking, the body accelerates during the second half of the phase in which the foot touches the ground, before it decelerates. Recently developed real-time ultrasound imaging makes it possible to observe the behavior of the muscle-tendon complex during walking. Muscle fiber (MF) of the m. gastrocnemius medialis (MG), which acts as one of the main agonist muscles, contracted isometrically during the body acceleration phase, whereas the MG tendinous tissue (TT) was lengthened. Before toe clearance, both the MF and TT shortened drastically without MG activation. No mechanical power exerted by the MF contraction was observed while the foot was on the ground, but the TT provided mechanical power in lengthening (negative) following the shortening (positive) during the body acceleration phase. It was observed that during walking the MG fiber contracts isometrically whereas the tendinous tissue is stretched, causing the storage of elastic energy in tendinous tissue. Before toe clearance, the abrupt shortening of tendinous tissue and total muscle-tendon complex is caused by release of the elastic energy stored in tendinous tissue.

A new dynamometer was developed for the measurement of specific movement power (SMP) exerted by mono- or multi-articular movements. To determine the reproducibility of SMP, two identical test protocols were carried out on separate days for six movement types on seven adult males. The movement types were arm pull (AP), leg rise (LR), knee extension (KE), elbow flexion (EF), hip extension (HE) and squat movement (SQ). Variations in peak power obtained in two tests ranged from 0.7% (AP) to 9.6% (SQ). Coefficients of the test-re-test correlation in peak power ranged from 0.805 (SQ) to 0.961 (AP) and standard errors ranged from 4 W (EF) to 14 W (SQ). SMP in upper extremities increased from 166 TV (EF) to 307 W (AP) resulting from the increase in velocity. However, in the movements of lower extremities, SMP increased from 586 W (KE) to 1351 W (SQ) as a result of the increase in force. To evaluate the validity of the SMP, a pull movement in weightlifting was tested and related to the athletic performance on weightlifters. Positive linear correlation (r = 0.862, p&lt;0.001) was observed between SMP and the total weight best records. It is concluded that this newly developed dynamometer has enough reproducibility and validity for evaluating the SMP, which is developed by various joint movement patterns related to the sport. The feasibility of applying this measuring protocol to the testing and training programmes for improving the daily living activities and athletic performances should now be assessed.