Limited literature has investigated epidemiology of sports-related fatalities during high school organizes sports in Japan. Therefore, the purposes of this study are to determine the frequency and incidence rate of sports-related fatalities in Japanese high schools by cause and sports, and to examine the type of on-site first responder. Insurance claim data of sports-related fatalities in Japanese high schools reported to Japan Sports Council Injury and Accident Mutual Aid Benefit System between 2009 and 2018 were retrieved as the primary data source. All fatalities were classified into direct or indirect type by the reported etiology and further categorized into cardiac-related, head and neck injury, exertional heat stroke (EHS), or other. Frequency and incidence rate were calculated by cause of death and sports, and incidence rates were expressed per 100,000 athlete-years (AY) with 95% confidence interval (CI). Information regarding first responder to the incident was also retrieved and examined by frequency. A total of 63 sports-related fatalities were analyzed. The overall incidence rate was 0.45 (95%CI = 0.25–0.65) per 100,000AY. The incidence rates of direct and indirect fatalities declined from 0.36 and 0.50 per 100,000AY to 0.28 and 0.00 per 100,000AY, respectively. The leading cause of deaths was cardiac-related (n = 30/63, 47.6%), followed by head and neck injury (n = 15/63, 23.8%) and EHS (n = 14/63, 22.2%). The number of fatalities was highest in male baseball (n = 12/63, 19.0%) and the incidence rate was highest in male judo (4.79 per 100,000 AY, 95%CI: 0.68–8.15). Coach was the most frequently reported first responder onsite (n = 52/63, 82.5%). Medically trained personnel were involved in onsite care in two cases (3.2%). In conclusion, the occurrence of sports-related fatalities has declined over time from 2009 to 2018. To deliver appropriate medical care onsite for better survival, employment of medically trained personnel should be promoted in high school sports setting in Japan.

PURPOSE: To evaluate the effect of the number of high-acceleration movements on muscle damage and the rating of perceived exertion (RPE) in basketball games. METHODS: Twenty-one male collegiate basketball players (mean age, 20.0 [1.0] y) were included. A triaxial accelerometer was used to measure acceleration in basketball-simulated scrimmages. To detect higher physical load during the actual game, the resultant acceleration was calculated, and 3 thresholds were set: >4G, >6G, and >8G resultant accelerations. The number of the extracted movements was calculated at each acceleration threshold. Plasma creatine kinase (CK) levels (marker of muscle damage) were estimated before and 24 hours after the match, and the session-RPE load was calculated within 30 minutes after the match. Pearson product-moment correlations with 95% confidence intervals were used to determine the relationships between the number of high-acceleration movements and plasma CK and session-RPE load. RESULTS: Significant correlations were observed between the number of high-acceleration movements >8G and CK level (r = .74; 95% confidence interval, 0.44-0.89; P < .0001). Furthermore, the correlation coefficient between acceleration and CK increased with increased acceleration threshold (>4G: r = .65; >6G: r = .69). Contrastingly, the correlation coefficient between acceleration and the session-RPE load decreased with increased acceleration threshold (>4G: r = .72; >6G: r = .52; >8G: r = .43). CONCLUSIONS: The session-RPE reflects the total amount of movement, while the high-acceleration movement reflects the momentary large impact load or intensity, and they evaluated different factors. Basketball coaching and conditioning professionals recommended combining acceleration and session-RPE when monitoring the load of athletes.

The ideal timing to implement anterior cruciate ligament injury prevention programs with respect to maturation is unclear. The purpose of this study was to investigate the effects of an injury prevention program on knee mechanics in early-, late-, and postpubertal females. In the study, 178 adolescent female basketball players were assigned to six groups: early-pubertal training, early-pubertal control, late-pubertal training, and late-pubertal control, post-pubertal training, and post-pubertal control. The training groups performed an injury prevention program for six months. Medial knee displacement, knee flexion range of motion, and the probability of high knee abduction moment were assessed before and after the training period. After the six-month training period, medial knee displacement was significantly increased in the early-pubertal control group whereas it was unchanged in the early-pubertal training group. Knee flexion range of motion was significantly decreased in the early-pubertal control group whereas it did not change in the early-pubertal training group. The probability of high knee abduction moment was increased in the early-pubertal control group whereas it was unchanged in the earl-pubertal training group. The probability of high knee abduction moment was also decreased in the post-pubertal training group whereas it did not change in the post-pubertal control group. The program limited the development of high-risk movement patterns associated with maturation in early puberty while improving the knee mechanics in post-pubertal adolescents. Therefore, an injury prevention program should be initiated in early puberty and continue through the post-puberty years.

The purpose of this study was to examine whether the NHE with an increased lower leg slope angle would enhance hamstring EMG activity in the final phase of the descend. The hamstring EMG activity was measured, the biceps femoris long head (BFlh) and the semitendinosus (ST). Fifteen male volunteers participated in this study. Subjects performed a prone leg curl with maximal voluntary isometric contraction to normalize the hamstring EMG activity. Subsequently, subjects performed the NHE, with the help of a certified strength and conditioning specialist, while the lower leg slope angle were randomly set at 0 degrees (NH), 20 degrees (N20), and 40 degrees (N40). To compare hamstring EMG activity during the NHE variations, the knee flexion angle was set in the range from 0 degrees to 50 degrees, divided into five phases (0-10 degrees, 10-20 degrees, 20-30 degrees, 30-40 degrees and 40-50 degrees), where 0 degrees indicated that the knee was fully extended. To calculate the knee extension angular velocity, the knee flexion angle divided by time, and break point angle (BPA) was the angle at which 10 degrees/s was exceeded. In the statistical analysis, a two-way repeated measures ANOVA was used for the hamstring EMG activity and a one-way repeated measures ANOVA was used for the BPA. The EMG activity of the BFlh and the ST in N20 and N40 was significantly higher than in NH at knee flexion angle of 0-20 degrees (p < 0.05). For the BPA, NH (57.75 degrees +/- 13.28 degrees), N20 (36.27 degrees +/- 9.89 degrees) and N40 (16.26 degrees +/- 9.58 degrees) were significantly higher in that order (p < 0.05). The results of this study revealed that the NHE with an increased lower leg slope angle shifted the BPA to the lower knee flexion angle and enhanced the hamstring EMG activity in the final phase of the descent.

OBJECTIVES: This study aimed to clarify the kinematic, kinetic characteristics associated with lateral ankle sprain. DESIGN: A 16-month prospective cohort study. SETTING: Laboratory. PARTICIPANTS: A total of 179 college athletes. MAIN OUTCOME MEASURES: Joint kinematics, moment during single-leg landing tasks, and ankle laxity were measured. The attendance of each participating team, injury mechanism, existence of body contact, presence of orthosis, with or without medical diagnosis, and periods of absence were recorded. RESULTS: Twenty-nine participants incurred lateral ankle sprain during non-contact motion. The Cox regression analysis revealed that greater knee varus peak angle (hazard ratio: 1.16 [95% confidence interval: 1.10-1.22], p < 0.001) and greater pelvic internal rotation peak angle toward the support leg were associated with lateral ankle sprain (hazard ratio: 1.08 [95% confidence interval: 1.02-1.15], p = 0.009). The cut-off values for each predictive factor were -0.17° (area under the curve = 0.89, p < 0.001) and 6.63° (area under the curve = 0.74, p < 0.001), respectively. CONCLUSIONS: A greater knee varus peak angle and pelvic internal rotation peak angle after single-leg landing are predictive factors for lateral ankle sprain.

OBJECTIVE: This study aimed to compare the effect of different density foam rollers on range of motion recovery. METHOD: Ten active men completed two, 3-day trials in random order. During the experimental trials, all participants performed 2 min of foam rolling (FR) using a medium-density (medium trial) or hard-density (hard trial) foam roller on the right posterior thigh after completing the 90-min Loughborough Intermittent Shuttle Test (LIST). The hip joint range of motion (ROM), muscle hardness, and muscle soreness were assessed before and after the LIST and at 0 min, 20 min, 60 min, 24 h, and 48 h after FR intervention. Serum creatine kinase (CK) concentrations were assessed before the LIST and at 60 min, 24 h, and 48 h after FR intervention. The contralateral leg in each trial was used as a control. RESULTS: The ROM at 0 min, 20 min, 60 min, 24 h, and 48 h after FR intervention were higher in the right leg (the massage leg) than in the left leg (the contralateral leg) (p < 0.05). In the right leg, the ROM at 0 min after FR intervention was higher than after the LIST (p < 0.05). There were no significant differences between the medium and hard trials for ROM. Muscle hardness, muscle soreness, and serum CK concentration were not affected by FR. CONCLUSION: FR has a positive effect on ROM recovery. Moreover, the two roller densities provided similar ROM recovery.

The semitendinosus (ST) muscle is primarily used during Nordic hamstring exercise (NHE), which is often prescribed for preventing hamstring injury, though the biceps femoris long head (BFlh) muscle that is more susceptible to injuries. Thus, this study aimed to identify the modulation of BFlh muscle activity with different knee flexion angles during NHE using an inclined platform. Fourteen male athletes performed NHE and maintained their position at maximum inclination (NH). Subjects also performed isometric NHE using a platform inclined to 50° (ICL) and 40° (ICH), and the knee flexion angle was controlled to 50° and 30°. The electromyography (EMG) activity of the BFlh, ST, semimembranosus, gluteus maximus, elector spinae, and rectus abdominus muscles was determined during each exercise. The EMG of the ST was higher than that of the BFlh during NHE and the highest of all muscles in all exercises (p &lt; 0.05). Moreover, the activity of the BFlh tended to be higher than that of the ST for ICH than for ICL, regardless of the knee joint angle. The activity of the BFlh becomes equivalent to that of the ST during NHE at a knee flexion angle of less than 50°. These results indicate that performing NHE at a shallow knee flexion angle will enhance the activity of the BFlh muscle.

This study aimed to investigate the influence of the task type on the relative electromyography (EMG) activity of biceps femoris long head (BFlh) to semitendinosus (ST) muscles, and of proximal to distal regions during isometric leg-curl (LC) and hip-extension (HE). Twenty male volunteers performed isometric LC with the knee flexed to 30° (LC30) and 90° (LC90), as well as isometric HE with the knee extended (HE0) and flexed to 90° (HE90), at 40% and 100% maximal voluntary contraction (MVIC). Hip position was neutral in all conditions. EMG activity was recorded from the proximal and distal region of the BFlh and ST muscles. BFlh/ST was calculated from the raw root-mean-square (RMS) amplitudes. The RMS of 40% MVIC was normalized using MVIC data and the proximal/distal (P/D) ratio of normalized EMG (NEMG) was calculated. The BFlh/ST ratio was higher in HE0 than in LC90 during MVIC and 40% MVIC (p<0.05), and was higher in HE90 than in LC90 (p<0.05) during 40% MVIC at the proximal region, whereas no difference was observed between HE0 and LC30. There was no inter-task difference in BFlh/ST ratio in the distal region. Furthermore, the P/D ratio was higher in LC90 than in LC30 and HE0 (p<0.05) in BFlh and ST muscles, and was higher in HE90 than in LC30 and HE0 (p<0.05) in BFlh during 40% MVIC. However, there was no difference in P/D ratio between LC30 and LC90, and HE0 and HE90. This showed that there was no task-dependent difference in the EMG activity of the BFlh muscle relative to the ST muscle between prone hip extension and prone knee flexion when the knee joint was set at an equivalent angle. Similarly, there was no task-dependent difference in the NEMG of the proximal region relative to the distal region in BFlh and ST muscles during 40% MVIC.

<italic><bold>Context</bold>:</italic> This study aimed to examine the differences in electromyographic (EMG) activity of the biceps femoris long head (BFlh) and semitendinosus (ST) muscles, break-point angle (BPA), and the angle at peak BFlh EMG activity between bilateral and unilateral Nordic hamstring exercise (NHE) on a sloped platform. <italic><bold>Design</bold>:</italic> This study was designed as a case-control study. <italic><bold>Methods</bold>:</italic> Fourteen men participated in the study. The participants initially performed maximum voluntary isometric contraction (MVIC) on the prone leg curl to normalize the peak hamstring EMG amplitude as the %MVIC. Then, participants were randomized to perform the following 3 variations of NHE: bilateral (N40) or unilateral (N40U) NHE with a platform angle of 40°, and unilateral NHE with a platform angle of 50° (N50U). The EMG activities of the BFlh and ST and the knee flexion angle during the NHE variations were recorded to calculate the EMG activity of the BFlh and ST in terms of the %MVIC, the angle at peak BFlh EMG, and BPA. <italic><bold>Results</bold>:</italic> The BFlh %MVIC was significantly higher in N40U (<italic>P</italic> &lt; .05) and N50U (<italic>P</italic> &lt; .05) than in N40. A significant difference in BFlh %MVIC and ST %MVIC was observed between N40U (<italic>P</italic> &lt; .05) and N50U (<italic>P</italic> &lt; .05). The mean values of BPA and the angle at peak BFlh EMG were &lt;30° for all NHE variations. <italic><bold>Conclusions</bold>:</italic> In the late swing phase of high-speed running, BFlh showed higher EMG activity; thus, unilateral NHE may be a specific hamstring exercise for hamstring injury prevention.

<p>股関節・鼠径部痛（Groin Pain:以下GP）の既往者におけるランニング動作の特徴を3次元動作解析を用いてバイオメカニクス的に明らかにすることを目的とした．過去1年間に股関節・鼠径部に痛みを有したことがある脚，11脚を股関節・鼠径部痛群（GP群）とし，痛みの既往がない脚，14脚をコントロール群（C群）として検討を行った．結果，GP群のランニングの特徴として支持期において遊脚側の骨盤が下制しているトレンデレンブルグ徴候が認められた．また股関節は内転位となり，足関節は回外から回内への角度変化が少なかった．GPのリハビリテーション・予防にはランニング動作における骨盤，股関節，足関節運動の改善の必要性が示唆された．</p>

Purpose: Lateral ankle sprain (LAS) in childhood can result in lateral malleolus avulsion fractures; additionally, bone nonunion may occur. Physical maturity relates to the development of bone morphology and physical functionality. It is unknown how changes in physical functionality attributable to physical maturity affect young soccer players with abnormal lateral malleolus (ALM) morphology. Hence, the present study aimed to investigate the bone morphology of the lateral malleolus in young soccer players and to examine its relationship with physical functionality at different maturity levels.Subjects and Methods: Two hundred and ninety young soccer players aged 6-15 years were included. The presence of ALM was assessed using ultrasonography. The subjects were allocated to three groups based on physical maturity (Pre-, Mid-, and Post-peak height velocity age [PHVA]). The prevalence of ALM and the relationship between ALM and physical maturity were examined for body composition, foot pressure distribution, foot alignment, ankle mobility, and single-leg balance.Results: The prevalence of ALM was 17.6%. For physical maturity, the post-PHVA group showed a decrease in ankle dorsiflexion and eversion and an increase in one-leg hop distance compared to the Pre-PHVA group (P < 0.05). In the ALM group, the center of pressure during heel raising was distributed laterally in the Post-PHVA (P < 0.01), and the weight-bearing dorsiflexion angle was decreased in the Mid- and Post-PHVA (P < 0.05).Conclusion: In the Post-PHVA young soccer players, decreased ankle dorsiflexion and eversion and increased one-leg hop distance were observed. The ALM group exhibited lateral loading during heel raising in the Post-PHVA group and decreased weight-bearing ankle dorsiflexion angle in the Mid- and Post-PHVA groups. The findings indicate the importance of secondary prevention of LAS and ultrasonography. Prospective studies of LAS in young athletes are required in the future.

Although a 3- to 7-min re-warm up (RW) elicits performance and physiological benefits after half-time (HT), a time-efficient and feasible RW protocol is required for the use of an RW in the athletic setting. This study aimed to investigate the effect of a 1-min RW at high-intensity on the performance and physiological responses during the Loughborough Intermittent Shuttle Test (LIST). In a randomized and counterbalanced cross-over design, 12 male amateur intermittent team sports players (soccer, basketball, handball, and lacrosse; age, 22 +/- 2 years; height, 1.70 +/- 0.08 m; body mass, 65.1 +/- 8.3 kg; body mass index, 22.4 +/- 1.9 kg m(-2); VO2max, 53.5 +/- 4.5 ml kg(-1) min(-1)) performed the LIST. The LIST comprised two 45-min halves separated by a 15-min HT. Each half comprised repetitions of exercise cycles consisting of 3 x 20-m walking, 1 x 20-m maximal sprint, 3 x 20-m jogging, and 3 x 20-m running. During the HT, the participants were assigned to a control trial (CON; 15-min seated rest) or an RW trial (1-min running at 90% of the maximal oxygen uptake after a 14-min seated rest). Compared to the CON, the RW prevents reductions in sprint performance at the fourth and sixth periods of the LIST (fourth: 2.4%, p = 0.002, d = 1.68, sixth: 3.6%, p = 0.012, d = 1.74) and a decrement of gastrointestinal temperature during HT (0.5 degrees C, p = 0.010, d = 1.41). Moreover, the RW decreased the electromyogram amplitude of maximal voluntary contraction (MVC) after HT (12%, p = 0.017, d = 1.12) without a decrease of maximal voluntary contraction force, suggesting an increased neuromuscular efficiency (9%, p = 0.048, d = 0.58). The RW also increased the mean heart rate in the initial part of the second half (4 bpm, p = 0.016, d = 0.38). In conclusion, the RW improved sprint performance, core temperature, muscle activation, and heart rate in the second half of the LIST. The findings suggest that the RW should be recommended for intermittent team sports players when longer RWs are not possible.

In this study, we investigated differences in electromyographic activity in the biceps femoris long head (BFl), semitendinosus, and semimembranosus muscles during 45° hip extension with different knee angles during eccentric, concentric, and isometric hip 0°, and isometric hip 45° conditions with non-external resistance and 5-kg load. Twenty-two male volunteers performed 45° hip extension with knee flexion angles of 0°, 45° and 90° with non-external resistance and 5-kg load eccentric, concentric, isometric hip 0°, and isometric hip 45° conditions. The electromyographic data obtained during each condition were normalized with the values collected during maximal voluntary isometric contraction of each muscle. A multivariate analysis of variance with repeated measures using syntax was used to compare the normalized electromyography of each muscle across different knee joint angles in each weight condition. Electromyographic activities of the BFl, semitendinosus, and semimembranosus at 45° and 90° knee flexion angles were significantly greater than at 0° in the eccentric, concentric, isometric hip 0°, and in isometric hip 45° conditions with both non-external resistance and 5-kg load (p<0.05), except for that of the BFl and semitendinosus in isometric hip 45° with 5-kg load. The electromyographic activity of the BFl was significantly higher than that of the semimembranosus at 90° knee flexion in all conditions (p < 0.05), except during eccentric with non-external resistance. There was no significant difference in electromyographic activity in the hamstring muscles among different knee angles and muscular contraction conditions. This study showed that 45° hip extension with 45° and 90° knee flexion might be better in terms of the recruiting hamstring activity compared to 0° knee flexion, regardless of the training intensity. We recommend 45° hip extension exercises with knee flexion angles of 45° and 90° to activate the BFl, in preventing hamstring strain.

Background: Little is known about the activity of the abdominal internal oblique (IO) and lumbar multifidus (LM) muscles relative to kinetic chain exercises performed in a standing position.Hypothesis/Purpose: The purpose of this study was to identify the activity of the IO and the LM muscles during weight-bearing exercises. The authors hypothesized that IO and LM muscle activity would vary with lower body positions during the kinetic chain exercises.Methods: Nineteen healthy, young, active subjects volunteered to participate. The electromyographic (EMG) activity (via surface EMG) of the abdominal external oblique (EO), IO, and LM muscles on both sides and the rectus femoris and semitendinosus muscles on the dominant side was determined during rhythmical lower body twisting exercise with three lower body positions: straight leg (SL), athletic position (AP), dynamic knee extension (DE) at two exercise speeds: 150 and 90 beats per min. These were reported as % maximum voluntary contraction. Mean EO, IO, and LM muscle activities were also compared with those of common core stability exercises.Results: IO EMG activity was significantly greater in SL than that of AP (p < 0.05). In contrast, LM EMG activity was significantly greater in the DE position than that of both SL and AP positions (p < 0.05).Conclusion: IO muscle activity could be attenuated by the contraction of lower body extensor muscles during the standing position.

This study investigated the effect of high-intensity cycling re-warm up (RW) within a very short time-frame on the subsequent intermittent sprint performance. Twelve active males completed three trials in random order: control (CON); 3-min RW at 30% of maximal oxygen uptake (VO2max) (RW30); and 1-min RW at 90% of VO2max (RW90). During the experimental trials, participants performed 40-min intermittent cycling exercise followed by 15-min rest. During the rest period, participants completed CON, RW30, or RW90. After the rest period, participants performed the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10-s rest, 5-s maximal sprint, and 105-s active recovery with the cycles repeated over 10 min. The mean work during sprint for the CISP was significantly higher in both RW trials than in the CON trial (mean +/- standard deviation; CON: 3539 +/- 698 J; RW30: 3724 +/- 720 J; RW90: 3739 +/- 736 J; p<0.05). The mean electromyogram amplitude during the sprint for the CISP was higher in the RW30 trial than in the CON trial; however, there was no significant difference between the two trials (p=0.06). The mean median frequency during sprint for the CISP was significantly higher in the RW90 trial than in the other trials (p<0.05). Rectal temperature did not differ among the three trials. Oxygenated haemoglobin during the initial 30 s of the CISP was significantly higher in the RW90 trial than in the CON trial (p<0.05). Compared with seated rest, RW, irrespective of whether it comprised 1-min at 90% of VO2max or 3-min at 30% of VO2max, increased the subsequent intermittent sprint performance.

Context: Several studies have reported that self-massage using a foam roller (FR) increased joint range of motion (ROM) immediately. However, the mechanism of increasing ROM by the FR intervention has not been elucidated. Objective: To clarify the mechanism by investigating properties and morphological changes of muscles targeted by the FR intervention. Design: An interventional study. Setting: An athletic training laboratory. Participants: Ten male college volunteers with no injuries in their lower limbs (mean [SD]: age 23.8 [3.2] y, height 173.2 [4.9] cm, weight 69.5 [8.6] kg). Intervention: The FR intervention on the right plantar flexors for 3 minutes. Main Outcome Measures: Maximum ankle ROM, muscle hardness, and fascicle length of the gastrocnemius muscle at the neutral (0 degrees), maximum dorsiflexion, and maximum plantar flexion positions. All measurements were conducted before (PRE) and after (POST) the FR intervention. Results: Dorsiflexion ROM increased significantly at POST (PRE: 13.6 degrees [8.01, POST: 16.6 degrees [8.4 degrees]; P < .001), although plantar flexion ROM did not change significantly between PRE and POST (PRE: 40.0 degrees [6.1 degrees], POST: 41.1 degrees [4.9 degrees]). There was no significant difference in muscle hardness and fascicle length between PRE and POST in any of the angles. Conclusions: Dorsiflexion ROM increased significantly by the FR intervention in the present study; however, muscle hardness and fascicle length did not change. FR may affect not only the muscle but also the fascia, tendon, and muscle-tendon unit. The FR protocol of the present study can be applied in clinical situations, because it was found to be effective to increase ROM.

Purpose:Proprioceptive function of the lower limbs deteriorates in patients following total hip arthroplasty. Patients show poor balance and rely more on visual information than proprioceptive information. Plantar vibration stimuli can mechanically enhance somatosensory input from the plantar cutaneous mechanoreceptors, thereby improving static balance. Plantar vibration stimuli may improve static balance in patients after total hip arthroplasty. This is the first study to investigate whether plantar vibration stimuli affects static balance during the early phase following total hip arthroplasty. Materials and methods:In this cross-over design study, 16 female patients (aged 65.1 +/- 11.0 years) received plantar vibration stimuli for 2 minutes or the sham interventions after total hip arthroplasty in a randomized order on different days. The foot centre of pressure was measured for the total path length, mediolateral path length, and anteroposterior path length directions before and immediately after the interventions in the static standing position both with eyes open and closed. Patients were instructed to minimize body sway when standing. Results:A significant increase was observed in the centre of pressure parameters in the eyes closed condition than in the eyes open condition. The centre of pressure parameters for the eyes closed condition was significantly decreased after vibration interventions than that before intervention. Conclusions:This study supports the view that plantar vibration stimuli can change static balance in patients in the early phase after total hip arthroplasty temporarily by up-weighting sensory information. These stimuli may serve as a treatment option for influencing balance following total hip arthroplasty.

Koyama, T, Rikukawa, A, Nagano, Y, Sasaki, S, Ichikawa, H, and Hirose, N. Acceleration profile of high-intensity movements in basketball games. J Strength Cond Res XX(X): 000-000, 2020-This study aimed to elucidate movements that require greater acceleration during basketball games, their occurrence frequency, and compare acceleration components. Eighteen male collegiate basketball players (age: 19.5 ± 0.8 years) were enrolled. Triaxial accelerometer was used to measure acceleration and a synchronized video was recorded. Moments that generated resultant accelerations >4, 6, and 8 G, and their coincided movements were identified. Ratios and frequencies of the extracted movements were calculated and Jonckheere-Terpstra trend test was used to examine which movement rate increased when acceleration threshold increased. In addition, the top 7 movements that generated a resultant acceleration >6 G among the combination of basketball-specific movements were extracted. Their resultant, mediolateral, vertical, and anteroposterior accelerations were identified and compared using one-way analysis of variance. Cohen's d was used to calculate effect sizes. All p < 0.05 were considered statistically significant. The extracted frequencies were 33.6, 9.1, and 2.3 cases per minute for >4 G, >6 G, and >8 G, respectively. As the threshold increased, the rate of deceleration, landing, and physical contact increased. The mediolateral acceleration of physical contact was significantly greater than other movements, whereas the vertical acceleration of landing and deceleration was significantly greater than other movements. Thus, acceleration component analysis was performed to classify movement types. Greater acceleration appeared frequently in movement during defense. It is suggested that many defense movements involve a reaction to the ball and opponent. There are many passive movements during defense and speed changes rapidly. If many passive movements occur when defending, larger physical load is applied, and may lead to fatigue.

Itoh, R and Hirose, N. Relationship among biological maturation, physical characteristics, and motor abilities in youth elite soccer players. J Strength Cond Res 34(2): 382-388, 2020-Studies investigating skeletal maturity and motor abilities in youth Asian elite soccer players are lacking. We aimed to investigate the cross-sectional relationship among skeletal age (SA), physical characteristics, and motor abilities in youth elite soccer players. Skeletal age is commonly used to estimate the maturity status of youth athletes using a hand-wrist radiograph. We enrolled 49 youth elite male soccer players (12.7 ± 0.2 years). Height, body mass, body fat percentage, circumference (thigh/calf), flexibility, 10-m/50-m sprint, 10-m × 5 shuttle run, the crank test, 5-step bounding, Yo-Yo intermittent recovery test level 2, and cooper run were measured. Participants were divided into early (n = 14), average (n = 22), and late (n = 13) maturation groups according to their chronological age (CA) and SA based on the following criteria: SA-CA < -1 year, SA-CA = ±1 year, and SA-CA > +1 year, respectively. The difference in parameters among the groups was analyzed using one-way analysis of variance and Tukey's post hoc test. Statistical significance was set at p < 0.05. The early and average maturation groups were taller and heavier and had a larger circumference than the late maturation group (p < 0.05). Conversely, the early and average groups were significantly faster in 50-m sprint (p < 0.05) and scored higher in 5-step bounding (p < 0.05) than the late group. There was no difference in other parameters among the groups. In conclusion, the difference in biological maturity influences physical and physiological development, particularly height and muscular power, in youth elite soccer players.

Ankle sprains are the most prevalent injuries, and elevated fear avoidance beliefs after ankle sprain episodes could inhibit athletic performance and contribute to residual symptoms, such as functional and/or mechanical instability. However, it remains unclear how fear avoidance beliefs differ according to conditions of posttraumatic sequelae. The purpose of this study was to determine whether fear of movement/reinjury differed between individuals with and without functional ankle instability (FI, NFI) and healthy controls (CON) and to examine the relationship between fear and ankle joint laxity by sex. Participants (115 male athletes, 105 female athletes) completed the Identification of Functional Ankle Instability, Athlete Fear Avoidance Questionnaire (AFAQ), Tampa Scale for Kinesiophobia (TSK), and ankle joint laxity test. Total 168 athletes (79 males, 89 females) data were eligible for analysis. The results demonstrated that fear of movement/reinjury was lower in individuals in the absence of functional ankle instability although they experienced ankle sprain (FI; TSK=38.6±4.5, AFAQ=27.4±6.2, NFI; TSK=35.7±5.6, AFAQ=24.5±6.6). The fear of movement/reinjury had correlation with ankle joint laxity only in female athletes (TSK; r=0.285, p=0.013, AFAQ; r 0=0.322, p=0.045).

Previous studies suggest that marathon running induces lower extremity muscle damage. This study aimed to examine inter- and intramuscular differences in hamstring muscle damage after a marathon using transverse relaxation time (T2)-weighted magnetic resonance images (MRI). 20 healthy collegiate marathon runners (15 males) were recruited for this study. T2-MRI was performed before (PRE) and at 1 (D1), 3 (D3), and 8 days (D8) after marathon, and the T2 values of each hamstring muscle at the distal, middle, and proximal sites were calculated. Results indicated that no significant intermuscular differences in T2 changes were observed and that, regardless of muscle, the T2 values of the distal and middle sites increased significantly at D1 and D3 and recovered at D8, although those values of the proximal site remained constant. T2 significantly increased at distal and middle sites of the biceps femoris long head on D1 (p = 0.030 and p = 0.004, respectively) and D3 (p = 0.007 and p = 0.041, respectively), distal biceps femoris short head on D1 (p = 0.036), distal semitendinosus on D1 (p = 0.047) and D3 (p = 0.010), middle semitendinosus on D1 (p = 0.005), and distal and middle sites of the semimembranosus on D1 (p = 0.008 and p = 0.040, respectively) and D3 (p = 0.002 and p = 0.018, respectively). These results suggest that the distal and middle sites of the hamstring muscles are more susceptible to damage induced by running a full marathon. Conditioning that focuses on the distal and middle sites of the hamstring muscles may be more useful in improving recovery strategies after prolonged running.

In this study, we aimed to clarify the characteristics of neuromuscular function, kinetics, and kinematics of the lower extremity during sprinting in track and field athletes with a history of strain injury. Ten male college sprinters with a history of unilateral hamstring injury performed maximum effort sprint on an athletic track. The electromyographic (EMG) activity of the long head of the biceps femoris (BFlh) and gluteus maximus (Gmax) muscles and three-dimensional kinematic data were recorded. Bilateral comparisons were performed for the EMG activities, pelvic anterior tilt angle, hip and knee joint angles and torques, and the musculotendon length of BFlh. The activity of BFlh in the previously injured limb was significantly lower than that in the uninjured limb during the late-swing phase of sprinting (p < 0.05). However, the EMG activity of Gmax was not significantly different between the previously injured and uninjured limbs. Furthermore, during the late-swing phase, a significantly more flexed knee angle (p < 0.05) and a decrease in BFlh muscle length (p < 0.05) were noted in the injured limb. It was concluded that previously injured hamstring muscles demonstrate functional deficits during the late swing phase of sprinting in comparison with the uninjured contralateral muscles.

Background: Throwing injuries of the shoulder and elbow are common among youth baseball players. Hypothesis: A prevention program will reduce the incidence of throwing injuries of the shoulder and elbow by 50% among youth baseball players. Study Design: Randomized controlled trial; Level of evidence, 1. Methods: The authors block randomized 16 youth baseball teams consisting of 237 players aged 9 to 11 years into an intervention group (8 teams, 117 players) and a control group (8 teams, 120 players). The intervention program consisted of 5 stretching, 2 dynamic mobility, and 2 balance training exercises performed during warm-up. Both groups were followed up for 12 months, during which the incidence of shoulder and elbow injuries was recorded. In addition, ball speed during pitching as a performance-related factor and variables of physical function (passive range of motion of the elbow, shoulder and hip, dynamic balance, and thoracic kyphosis angle) were assessed during the pre- and postintervention periods. Results: The incidence of shoulder and elbow injuries in the intervention group (1.7 per 1000 athlete-exposures) was significantly lower than that in the control group (3.1 per 1000 athlete-exposures) (hazard ratio, 1.940; 95% CI, 1.175-3.205; P = .010). The factors related to pitching performance, as assessed by ball speed, tended to increase in the intervention group as compared with the control group (P = .010). The program also improved shoulder horizontal adduction deficits on the dominant side, hip internal rotation on the nondominant side, and the thoracic kyphosis angle. Conclusion: A prevention program decreases throwing injuries of the shoulder and elbow and enhances the parameter of pitching performance in youth baseball players.

Yoshimura, A, Inami, T, Schleip, R, Mineta, S, Shudo, K, and Hirose, N. Effects of self-myofascial release using a foam roller on range of motion and morphological changes in muscle: a crossover study. J Strength Cond Res XX(X): 000-000, 2019-Self-myofascial release using a foam roller (FR) is effective in improving range of motion (ROM) in at least some conditions. However, its mechanism is still unclear. Therefore, this study investigated potential acute muscle morphological changes after the FR intervention and aimed to clarify the mechanism of increases in ROM by the FR intervention. We hypothesized that the FR intervention may increase ROM because of changes in fascicle length (FL) and aponeurosis displacement. This crossover study, involving 22 male university students (21.5 ± 1.3 years, 170.6 ± 4.0 cm, and 64.1 ± 8.9 kg; mean ± SD), compared the FR intervention targeting the gastrocnemius muscle with the control trial. The outcome measures were maximum passive ankle ROM, morphology of the gastrocnemius muscle (FL and aponeurosis displacement) during passive ankle plantar flexor movement, degree of pain during the FR intervention, and sensation of the triceps surae muscle. Although ROM of both dorsiflexion and plantar flexion increased significantly after the FR intervention (p < 0.01), no significant differences were found in FL and aponeurosis displacement before and after the FR intervention. The mean perception of pain during the FR intervention was rated as "slightly uncomfortable," corresponding to a 2.3 ± 2.4-cm on a 9.5-cm visual analog scale. We found that the FR intervention did not influence the morphology of muscle. It is necessary to investigate other factors related to ROM as the next step of this study.

Objective: Joint torque differences between healthy and rehabilitated legs are often measured as a clinical index of recovery from muscle strain injury. Unfortunately, it should be noted that this is a questionable evaluation measure of the muscle after injury because it is a composite value including related cooperating muscles. Meanwhile, the use of ultrasound elastography for the measurement of individual muscle mechanical properties (i.e., muscle hardness) has recently expanded. The purpose of this study was to examine, using ultrasound elastography, the differences in the linear relationship between muscle contraction intensity and muscle hardness during knee extension in athletes who had recovered from grade II rectus femoris muscle strain injury through comparison of the healthy and rehabilitated legs. Methods: Six athletes participated. Rectus femoris muscle hardness, determined during isometric contraction at 10%, 20%, 30%, and 40% of maximum voluntary contraction, was evaluated using ultrasound strain elastography. Results and Conclusion: The results indicated that for the healthy legs, the strain ratios, as indicated by muscle hardness, decreased linearly (became harder) with contraction intensity, but the strain ratios for the rehabilitated legs decreased nonlinearly. These results show the danger of judging the recovery period using only the difference between healthy and rehabilitated muscle strengths and the importance of evaluating individual muscles.

Objective: To assess the discriminability as well as the reliability, and internal consistency of the Identification of Functional Ankle Instability questionnaire translated into Japanese (IdFAI-J).Design: Cross-sectional study.Setting: Collegiate athletic training/sports medicine clinic.Participants: Twenty bilingual and sixty-five collegiate athletes including participants with and without functional instability (FI).Main outcome measures: The sensitivity, specificity, test retest reliability, and internal consistency of IdFAI-J.Results: The optimal cutoff score between the FI and non-FI participants was >10, with an area under the curve of 0.92. We calculated high sensitivity (0.94) and specificity (0.77) at the cutoff point. For the testretest reliability, the intraclass correlation coefficient value of the IdFAI-J was 0.96; the standard error of measurement and minimal detectable change value was 1.69 and 3.60, respectively. Cronbach's a was 0.87; there was no improvement when a particular item was deleted from the scale.Conclusions: The IdFAI-J has excellent discriminability, test-retest reliability, and internal consistency. Hence, the IdFAI-J significantly contribute to clinical practice and future research related to ankle instability in Japan. (C) 2018 Elsevier Ltd. All rights reserved.

This study investigated the effect of very-short-duration, low-intensity half-time re-warm up (RW) on subsequent intermittent sprint performance. Using a randomized cross-over design, 11 healthy men performed 3 trials. In the experimental trials, participants performed the first 40-minute intermittent exercise followed by a 15-minute half-time. The interventions at half-time were 15 minutes of seated rest (control), 3 minutes of moderate-intensity RW (cycling at 60% of maximal oxygen uptake [<(V)over dot>O(2)max]; [60% RW]), and 3 minutes of low-intensity RW (cycling at 30% of <(V)over dot>O(2)max; [30% RW]). After half-time, participants performed the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10 seconds of rest, 5 seconds of maximal sprint, and 105 seconds of active recovery at 50% of <(V)over dot>O(2)max, with the cycles repeated over the 20-minute duration. The mean work and electromyogram amplitude during the sprint in the CISP were higher in both RW trials than in the control trial (p < 0.05). Muscle temperature, estimated from the skin temperature, at 60 minutes was higher in the 60% RW trial than in the control and 30% RW trials (p < 0.05). The mean change in oxygenated hemoglobin concentration during active recovery at 55-65 minutes tended to be higher in both RW trials than in the control trial (60% RW trial: p = 0.06, 30% RW trial: p = 0.06). In conclusion, very-short-duration, low-intensity RW increased intermittent sprint performance after the half-time, in comparison with a traditional passive half-time practice, and was as effective as a moderate-intensity RW when matched for total duration.

Background: The Kerlan-Jobe Orthopaedic Clinic (KJOC) score has been used to describe various parameters of throwing shoulder and elbow function for the return to play after a long period of rehabilitation, such as after ulnar collateral ligament reconstruction. No study has yet to identify how scapular dyskinesis (SD) in baseball players affects the KJOC score. This study investigated the relationship of the KJOC score to SD evaluated in collegiate baseball players with and without upper extremity injury.Materials and methods: The study participants were 30 male collegiate baseball players (13 pitchers) belonging to the National Collegiate Athletic Association D-I conference. Participants were assessed with the KJOC instrument in the beginning (PRE) and end (POST) of the season. The SD test was conducted (PRE) in shoulder flexion to identify SD.Results: The mean value of KJOC. score was significantly less in POST than that of PRE for the pitchers with SD (89.3 and 60.5, respectively; P = .001), whereas no difference was found in the KJOC score between PRE and POST for the pitchers without SD. For the position players, no difference in the mean value of KJOC score was found between PRE and POST, regardless of SD.Conclusion: The results of this study provide evidence that collegiate baseball pitchers with mild SD may have lower KJOC scores, particularly setup or relief pitchers. (C) 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.

The purpose of the present study was to investigate the effect of different durations of half-time re-warm up (RW) on intermittent sprint performance. Using a randomized crossover design, 13 healthy men performed three trials, which consisted of two, 40-min intermittent exercises separated by a 15-min half-time. Half-time interventions were 15 min of seated rest (Control), 7 min of cycling at 70% of maximal heart rate (HRmax) (7 min RW), and 3 min of cycling at 70% of HRmax (3 min RW). The second 40-min intermittent exercise as an exercise performance test was the Cycling Intermittent-Sprint Protocol (CISP), which consisted of 10 s of rest, 5 s of maximal sprint, and 105 s of low-intensity exercise at 50% of VO2max, with the cycles repeated over the 40-min duration. The mean work during the maximal sprint in the initial 10 min of the CISP was higher in the both RW trials than in the control trial (control: 3638 +/- 906 J, 7 min RW: 3808 +/- 949 J, p < 0.05, 3 min RW: 3827 +/- 960 J, p < 0.05). There were no significant differences among three trials for mean work at 10-20, 2030, and 30-40 min of the CISP. In the initial 10 min of the CISP, the change in oxygenated hemoglobin concentration during the 105 s of exercise at 50% of VO2max, oxygen uptake, carbon dioxide production, and respiratory exchange ratio were higher in both RW trials than in the control trial (p < 0.05). The rating of perceived exertion after half-time interventions was higher in both RW trials than in the control trial (p < 0.05). In conclusion, the 3 min RW increased intermittent sprint performance after the half-time, compared with a traditional passive half-time practice, and was as effective in improving intermittent sprint performance as the 7 min RW.

© 2017 Springer International Publishing AG, part of Springer Nature An Online First version of this article was made available online at https://link.springer.com/article/10.1007%2Fs40279-017-0799-7on 29 October 2017. Errors were subsequently identified in the article, and the following corrections should be noted:

Background: Concussion causes acute, short-term brain dysfunctions. However, the impact of repetitive concussion history on brain function remains unclear. Objectives: The present study examined the effect of a history of multiple concussions on the cognitive functions and dynamic cerebral blood flow (CBF) regulation in collegiate rugby football players. Methods: Nine male rugby football players with a history of≤1 concussion and nine players with a history of multiple concussions (≤ 4 concussions) participated in this study. Reaction time and working memory were assessed using a neurocognitive assessment device (CogSport
CogState Ltd., Melbourne, Australia). Arterial blood pressure and middle cerebral artery blood velocity (MCAv) were measured continuously throughout the experiment. Dynamic cerebral autoregulation was examined using a thigh-cuff occlusion and release technique. Results:We found a significant difference in the short-term working memory between players with a history of ≤1 concussion and those with a history of multiple concussions (P &lt
0.05). However, dynamic cerebral autoregulation was not significantly different between the two groups. Conclusions: We found a dysfunction in the short-term memory function of collegiate rugby football players with a history of multiple concussions. However, this impairment in brain function was not associated with changes in dynamic CBF regulation.

Background: Programs to prevent anterior cruciate ligament (ACL) injuries in female basketball players are scarce. Also, ACL injury prevention training that focuses on hip joint function has not been reported.Purpose: To determine the effectiveness of a hip-focused ACL injury prevention program in female basketball players.Study Design: Cohort study; Level of evidence, 2.Methods: A prospective intervention study was conducted for 12 years. Incidence rates of ACL injuries were collected in the first 4 years (observation period) from college female basketball players. After the observation period, a hip-focused ACL injury prevention program was implemented for 8 years (intervention period). A total of 309 players (mean +/- SD age, 19.6 +/- 1.2 years; height, 163.7 +/- 5.6 cm; weight, 59.1 +/- 5.1 kg; body mass index, 22.0 +/- 1.4) were tracked in the observation period and compared with 448 players (age, 19.6 +/- 1.1 years; height, 162.6 +/- 5.8 cm; weight, 58.0 +/- 5.7 kg; body mass index, 21.9 +/- 1.5) who participated in the intervention period. Athlete-exposures (AEs), ACL numbers and mechanisms of injury (MOIs), relative risk (RR), absolute risk reduction (ARR), numbers needed to treat (NNT), and compliance were analyzed.Results: There were 16 ACL injuries (13 noncontact MOIs) in the 4-year observation period, whereas 9 ACL injuries (8 noncontact MOls) were recorded in the 8-year intervention period. The overall ACL injury incidence was 0.25/1000 AEs in the 4-year observation period compared with 0.10/1000 AEs in the 8-year intervention period, respectively. Compared with the 4-year observation period, significant RR reduction was observed (0.38; 95% CI, 0.17-0.87; P =.017) with ARR and NNT of 0.032 (95% CI, 0.027-0.037) and 31.6 (95% CI, 27.1-37.7), respectively, in the 8-year intervention period. The noncontact ACL injury incidence was 0.21 per 1000 AEs during the 4-year observation period compared with 0.08/1000 AEs in the 8-year intervention period, which also showed significant RR reduction (0.37; 95% CI, 0.15-0.92; P =.026), with ARR and NNT of 0.024 (95% CI, 0.020-0.029) and 41.3 (95% CI, 34.6-51.3), respectively. The mean compliance rate during the intervention periods (8 years) was 89%.Conclusion: A hip-focused injury prevention program demonstrated significant reduction in the incidence of ACL injury in female collegiate basketball players.

Background: Youth baseball players are at high risk for elbow injuries, which can lead to future functional disability.Purpose: To evaluate the effectiveness of a prevention program to lower the risk of medial elbow injury in these athletes.Study Design: Cohort study; Level of evidence, 2.Methods: Youth baseball players, 8 to 11 years old, without a history of elbow and shoulder pain, were allocated to either the intervention (n = 136) or control (n = 169) group. The intervention consisted of 9 strengthening and 9 stretching exercises, performed during warm-up or at home, with high compliance defined as completion of the program 1 or more times per week. The following outcome variables were measured: clinical assessment of the elbow and shoulder joint, ultrasonography assessment of the elbow, and assessment of physical function (passive range of motion of the elbow, shoulder, and hip; strength of the shoulder and scapular muscles; and measurement of the thoracic kyphosis angle). The clinical and ultrasonography assessments were measured at baseline and at 3-month intervals over the 1-year follow-up. Physical function outcomes were measured at baseline and at the endpoint of the follow-up. The primary endpoint of effectiveness was the incidence of medial elbow injury. Secondary endpoints were absolute measures of physical function and change in these measures over the 1-year follow-up.Results: The incidence rate of medial elbow injury was significantly lower in the intervention group (0.8/1000 athlete-exposures) than the control group (1.7/1000 athlete-exposures) (hazard ratio, 50.8%; 95% CI, 0.292-0.882; P = .016). The program improved total range of shoulder rotation (dominant side), hip internal rotation (nondominant side), shoulder internal rotation deficit (bilaterally), lower trapezius muscle strength (dominant side), and the thoracic kyphosis angle. Improvements in the following variables of physical function were predictive of a lower rate of medial elbow injury: increased total shoulder total rotation (odds ratio [OR], 0.973; 95% CI, 0.950-0.997), increased hip internal rotation of the nondominant side (OR, 0.962; 95% CI, 0.936-0.989), and decreased thoracic kyphosis angle (OR, 1.058; 95% CI, 1.015-1.103).Conclusion: A prevention program aiming to improve physical function can prevent medial elbow injury in youth baseball players.

[Purpose] The purpose of this study was to examine whether preventive rehabilitation improves the asymmetry between the involved side and the uninvolved side of single-leg landing, dynamic balance, and lower limb muscular strength of young female athletes after anterior cruciate ligament reconstruction (ACLR). [Subjects and Methods] The subjects were twelve young females who returned to sports after preventive rehabilitation after ACLR. Two-dimensional analyses of single-leg landing and lower limb muscular strength (knee extension/flexion, hip abduction/external rotation), and the modified star excursion balance test (M-SEBT) were performed at the time of the return. The difference between the involved side and the uninvolved side of each measure was compared, and the limb symmetry index (LSI) was calculated. [Results] There were no differences in knee valgus and flexion angle in single-leg landing, and in the M-SEBT. LSI of lower limb muscular strength was over 90%. [Conclusion] The asymmetry between the involved side and the uninvolved side was improved by preventive rehabilitation.

Background This study examines age-related changes in the quadriceps femoris (QF), subdivided into the vastus medialis oblique (VMO), vastus medialis (VM), rectus femoris (RF), vastus intermedius (VI) and vastus lateralis (VL) in basketball players. Subjects Seventy male basketball players were divided into four groups according to age (12-13, 14-15, 16-17, and 18-20 years). Methods Ultrasonography was used to measure muscle architecture of the VMO, VM, RF, VI and VL. We created cubic approximate expressions and calculated inflexion points to evaluate peak growth age of each muscle head. Results Significant interactions were observed for all QF parts (p < 0.01-0.001). Muscle thickness (MT) in all QF parts was significantly lower in 12-13-year olds than in 18-20-year olds (p < 0.01-0.001). Significant differences were recognised between 12-13 and 16-17-year olds in VM (p < 0.001), RF (p < 0.001) and VL (p = 0.007). MT was significantly lower in 14-15-year olds than in 16-17-year olds in the VM (p = 0.007) and RF (p = 0.026) and in 18-20 year olds in the VM (p < 0.001), RF (p = 0.036) and VI (p < 0.001). Peak growth age was estimated for each QF part (VMO, 155.0 months; VM, 187.8 months; RF, 212.2 months, VI, 188.9 months; VL, 181.1 months). Conclusion QF parts have different growth rates due to differing functions in each muscle head.

Background: The risk of anterior cruciate ligament (ACL) injury is higher in female soccer players than in male soccer players. The most common reason for non-contact ACL injury has been found to be a cutting or stopping maneuver combined with deceleration and landing from a jump. In a previous study, there was no difference in the incidence of ACL injury between offensive and defensive players and in the risk of ACL injury between goalkeepers and other players. Recently studies reported that the most frequent injury situation was pressing in male players. However, the most common type of situation associated with ACL injury in female soccer players has not been clarified. Objectives: The purpose of the present study was to identify the most common type of situation associated with ACL injury in female soccer players. Methods: We handed out questionnaires to 80 female soccer players with a history of ACL injury (90 ACL injuries). The players were asked about the injury characteristics, injury circumstance, maneuver being performed when the injury occurred, and playing type associated with the injury. The players responded to the questionnaire under the guidance of the medical staff of each team. Results: The 80 female soccer players reported a total of 90 ACL injuries during soccer. Among 55 non-contact injuries, 29 (55%) occurred during a cutting maneuver and 22 (44%) occurred during pressing. On assessing the frequency distributions of playing type (pressing vs. others) and body contact (contact vs. no contact), we found that non-contact injuries at pressing were significantly more common than contact injuries at pressing (odds ratio: 3.03
95% confidence interval, 1.11 - 8.25, P = 0.036) Conclusions: ACL injury often occurs as non-contact injury during pressing at the time of defense, regardless of the playing area, in female soccer players.

Background: There is a large amount of information regarding risk factors for fifth metatarsal stress fractures; however, there are few studies involving large numbers of subjects. This study aimed to compare the static foot alignment and distribution of foot pressure of athletes with and without a history of fifth metatarsal stress fractures.Methods: The study participants comprised 335 collegiate male soccer players. Twenty-nine with a history of fifth metatarsal stress fractures were in the fracture group and 306 were in the control group (with subgroups as follows: 30 in the fracture foot group and 28 in the non-fracture group). We measured the foot length, arch height, weight-bearing leg-heel alignment, non-weight-bearing leg-heel alignment, forefoot angle relative to the rearfoot, forefoot angle relative to the horizontal axis, and foot pressure.Results: The non-weight-bearing leg-heel alignment was significantly smaller and the forefoot angle relative to the rearfoot was significantly greater in the fracture foot group than in the control foot group (P = 0.049 and P = 0.038, respectively). With regard to plantar pressure, there were no significant differences among the groups. Midfield players had significantly higher rates of fifth metatarsal stress fracture in their histories, whereas defenders had significantly lower rates (chi-square = 13.2, P < 0.05). There were no significant differences in the frequency of fifth metatarsal stress fractures according to the type of foot (kicking foot vs. pivoting foot) or the severity of ankle sprain.Conclusions: Playing the midfield position and having an everted rearfoot and inverted forefoot alignment were associated with fifth metatarsal stress fractures. This information may be helpful for preventing fifth metatarsal stress fracture recurrence. More detailed load evaluations and a prospective study are needed in the future.

Introduction: Center of pressure (COP) is a sudden displacement at the time of a lateral ankle sprain (LAS). It has been suggested that the distribution of plantar pressure and the quantity of COP displacement are important for assessing the risk of LAS. Therefore, we evaluated the plantar pressure during a single-leg balance test with eyes closed (SLB-C) to identify the factors and characteristics of plantar pressure in people with repeated cases of LAS.Methods: We recruited 22 collegiate athletes and divided them into an instability group (IG; n= 11) and a control group (CG; n= 11). We measured the distribution of plantar pressure and lower extremity muscle activity during a SLB-C along with static alignment and isometric ankle strength.Results: The fibularis longus (FL) activity was significantly lower in the IG than in the CG. The lateral plantar pressure (LPP)/medial plantar pressure (MPP) ratio was also higher in the IG than in the CG. In addition, the LPP/MPP ratio was correlated with the tibialis anterior (TA)/FL ratio.Conclusion: These results suggest that increased lateral plantar pressure is related to decreased FL activity and increased TA/FL ratio.

This study aimed to investigate the in vivo kinematics of shear modulus of the lower leg muscles in patients with medial tibial stress syndrome (MTSS). The study population included 46 limbs with MTSS and 40 healthy limbs. The shear modulus of the medial head of the gastrocnemius, lateral head of the gastrocnemius, soleus, peroneus longus and tibialis anterior muscles were measured using shear wave ultrasound elastography. As a result, the shear modulus of the lower leg muscles was significantly greater in patients with MTSS than in healthy patients (p &lt; 0.01). Based on the differences in shear modulus of lower leg muscles between the patients with MTSS and healthy patients, the measurements obtained via shear wave ultrasound elastography could be used to evaluate risk factors of MTSS. (E-mail: kei.akiyama@jpnsport.go.jp) (C) 2016 World Federation for Ultrasound in Medicine & Biology.

Objectives: The present study examined 2-year changes in anthropometric variables and motor abilities in elite male youth soccer players to identify potential talent identification indexes.
Design: This was a cross-sequential study examining two different age groups at two time points.
Methods: Height, weight, 40-m sprint speed, muscular power (5-step bounding), and change of direction (COD) ability (10 m x 5 COD) were measured in 12- and 14-year-old soccer players and repeated after 2 years (at 14 and 16 years of age). Correlations and changes in ranking between the two measurements were determined.
Results: Both groups had small ranking changes in height (12-14-year-olds: r = 0.80, 14-16-year-olds: r=0.89; p &lt; 0.01), weight (r=0.94, r = 0.80; p &lt; 0.01), 40-m sprint speed (r = 0.81, r=0.90; p &lt; 0.01), and muscular power (r = 0.48, r = 0.64; p &lt;0.05), with a statistically significant correlation between the initial values and those obtained 2 years later. However, 10 m x 5 COD ability had a large ranking change, with no statistically significant correlation observed between the first- and second-year values.
Conclusions: Because of the minimal ranking change in sprint speed in normal circumstances of soccer practice, linear sprint speed has the potential to be a useful talent identification index for youth soccer players. On the other hand, muscular power and COD ability is changeable during growth period suggests that these parameters is not useful for talent identification index. (C) 2015 Sports Medicine Australia. Published by Elsevier Ltd. All rights reserved.

Objectives: The present study examined 2-year changes in anthropometric variables and motor abilities in elite male youth soccer players to identify potential talent identification indexes. Design: This was a cross-sequential study examining two different age groups at two time points. Methods: Height, weight, 40-m sprint speed, muscular power (5-step bounding), and change of direction (COD) ability (10 m × 5 COD) were measured in 12- and 14-year-old soccer players and repeated after 2 years (at 14 and 16 years of age). Correlations and changes in ranking between the two measurements were determined. Results: Both groups had small ranking changes in height (12-14-year-olds: r = 0.80, 14-16-year-olds: r = 0.89
p &lt
0.01), weight (r = 0.94, r = 0.80
p &lt
0.01), 40-m sprint speed (r = 0.81, r = 0.90
p &lt
0.01), and muscular power (r = 0.48, r = 0.64
p &lt
0.05), with a statistically significant correlation between the initial values and those obtained 2 years later. However, 10 m × 5 COD ability had a large ranking change, with no statistically significant correlation observed between the first- and second-year values. Conclusions: Because of the minimal ranking change in sprint speed in normal circumstances of soccer practice, linear sprint speed has the potential to be a useful talent identification index for youth soccer players. On the other hand, muscular power and COD ability is changeable during growth period suggests that these parameters is not useful for talent identification index.

【はじめに，目的】慢性足関節不安定症（CAI）は足関節捻挫受傷後の後遺症であり，足関節構造及び機能の問題から反復性の足関節捻挫を引き起こす。CAIは動作時に足関節運動の変化をもたらすと報告されているが，近年は膝関節運動にも変化が生じ，特に膝関節矢状面上での角度変化が報告されている。一方，足関節捻挫が頻発するとされるカッティング動作において膝関節運動を3運動面から詳細に検討した研究はない。本研究ではカッティング動作課題にて，Point Cluster法を用いてCAIの膝関節運動を詳細に検討した。【方法】被験者は健常群8名（男性4名，女性4名）とCAI群8名（男性4名，女性4名）とした。両群において身体的特徴に差は認められなかった。動作解析には3次元動作解析システム（Motion Analysis社）を用い，赤外線カメラ（Motion Analysis社；サンプリング周波数250Hz）8台，床反力計（Kistler社；サンプリング周波数1000Hz）1枚を使用した。被験者にはボディスパッツを着用で，Andriacchiら（J Biomech Eng, 1998.）の方法に基づき，身体の各ランドマークに加えて検査脚大腿部に10個，下腿部に6個のクラスターマーカーを，そして全身に41個の反射マーカーを貼付した。動作課題は1歩のサイドステップからの180度方向の方向転換動作とした。データは床反力垂直成分が10Nを超えた時間を初期接地（IC）と定義して，IC前後100msを解析区間とし，Point Cluster法を用いて膝関節屈曲・外転・内旋角度を算出した。膝関節の運動は，立位からの変位で示した。統計解析にはSPSS ver.22（International Business Machines社）を用い，健常群とCAI群のIC前後100msにおける膝関節角度の差を対応の無いt検定（有意水準95%）を行った。なお，時間の影響を考慮するため3データポイント以上連続して有意差が認められた場合のみ有意差ありとした。【結果】IC前100ms～68ms及びIC後40ms～80msにおいて健常群よりもCAI群の屈曲角度が有意に小さかった（p＜0.05）。また，IC前20ms～IC後36ms及びIC後52ms～76msにおいて健常群よりもCAI群の内旋角度が有意に小さかった（p＜0.05）。外転角度は2群間で有意差が認められなかった（p＞0.05）。【結論】本研究では新たな知見として，カッティング動作においてCAIはIC前後で膝関節内旋角度が小さくなる，つまり膝関節外旋傾向にあることが示された。接地時に足関節が固定された状態での膝関節外旋角度の増大は，足関節内旋ストレスを高めて足関節捻挫の受傷リスクを高める可能性がある。今後は足関節運動についても検討していく必要がある。また，膝関節のScrew home movementから，膝関節屈曲角度変化と膝関節内旋角度変化の関連性も考慮する必要がある。

Background: The rearfoot motion during sports activities in patients with the medial tibial stress syndrome (MTSS) is unknown. This study aimed to investigate the difference in kinematics of the rearfoot in MTSS patients (eight male soccer players) and control participants (eight male soccer players) during a forward step.
Methods: Sixteen male soccer players, including eight players with MTSS, participated. Forward step trials were recorded with cineradiographic images obtained at a sampling rate of 60 Hz. Geometric bone models of the tibia and talus/calcaneus were created from computed tomography scans of the distal part of one lower limb. Following a combination of approaches, anatomical coordinate systems were embedded in each bone model. The talocrural joint motion (relative motion of the talus with respect to the tibia) and subtalar joint motion (relative motion of the calcaneus with respect to the talus) were examined.
Results: A significantly larger range of internal/external rotation and inversion/eversion motion was observed in the subtalar joint of MTSS patients compared to healthy controls (P &lt; 0.05) from heel contact to heel off. There were no significant differences between the MTSS patients and healthy participants in the ranges of all talocrural joint angles during the forward step.
Conclusion: Our results indicate that the range of subtalar joint motion is greater in patients with MTSS during the stance phase of the forward step. The kinematic results obtained of this study may have important clinical implications and add quantitative data to an in vivo database of MTSS patients.

Purpose:To describe cross-sectional age differences in change-of-direction performance (CODp) in female football players and investigate the relationship between CODp and linear-sprint speed, muscle power, and body size. Methods: A sample of 135 well-trained female football players was divided into 8 age groups. Anthropometry (height, body mass, and lean body mass) and athletic performance (10-m sprint speed, 10-m x 5-CODp, and 5-step bounding distance) were compared to determine interage differences using ANOVA. Then, the participants were divided into 3 age groups: 12- to 14-y-olds, 15- to 17-y-olds, and &gt;= 18 y-olds. Simple- and multiple-regression analyses were conducted to determine the correlation between CODp and the other measurement variables in each age group. Results: Age-related differences were found for CODp (F = 10.41, P &lt; .01), sprint speed (F = 3.27, P &lt; .01), and bounding distance (F = 4.20, P &lt; .01). Post hoc analysis revealed that the CODp of 17-y-old players was faster than that of 16-y-old players (P &lt; .01), with no interage differences in sprint speed and bounding distance. Sprint speed and bounding distance were weakly correlated with CODp in 15- to &gt;= 18-y-old players, but only sprint speed was correlated with CODp in 12- to 14-y-old players. Conclusions: CODp improves from 16 to 17 y of age in female players. Linear-sprint speed, muscle power, and body size were weakly correlated with the age differences in CODp.

The purpose of this study was to identify the period of the gait cycle during which the hamstring muscles were likely injured by estimating the magnitude of tensile force in each muscle during overground sprinting. We conducted three-dimensional motion analysis of 12 male athletes performing overground sprinting at their maximal speed and calculated the hamstring muscle-tendon length and joint angles of the right limb throughout a gait cycle during which the ground reaction force was measured. Electromyographic activity during sprinting was recorded for the biceps femoris long head, semitendinosus, and semimembranosus muscles of ipsilateral limb. We estimated the magnitude of tensile force in each muscle by using the length change occurred in the musculotendon and normalized electromyographic activity value. The study found a quick increase of estimated tensile force in the biceps femoris long head during the early stance phase of the gait cycle during which the increased hip flexion angle and ground reaction force occurred at the same time. This study provides quantitative data of tensile force in the hamstring muscles suggesting that the biceps femoris long head muscle is susceptible to a strain injury during the early stance phase of the sprinting gait cycle.

The purpose of this study was to investigate growth changes in human plantar flexor muscle and tendons. In addition, we ascertained whether growth changes in muscle and tendon were more closely related to skeletal age than chronological age. 22 elementary school children (ESC), 19 junior high school students (JHS), and 23 young adults (ADT) men participated in this study. Maximal strain and hysteresis of tendon structures and cross-sectional area of Achilles tendon were measured using ultrasonography. In addition, skeletal age was assessed using Tanner-Whitehouse III method. Maximal strain of ESC was significantly greater than that of other groups, while no significant difference was observed between JHS and ADT. There was no difference in hysteresis among 3 groups. Relative cross-sectional area (to body mass 2/3) of ADT was significantly smaller than that of other groups. For ESC and JHS, measured variables of muscle and tendon were significantly correlated to both chronological and skeletal ages. These results suggested that immature musculoskeletal system was protected by more extensible and larger tendon structures in ESC and only by larger tendon structures in JHS, respectively. Furthermore, there were no differences in correlation coefficient values between measured variables of muscle and tendon and chronological or skeletal ages.

The purpose of this study was to compare the morphological and mechanical properties of the human patellar tendon among elementary school children (prepubertal), junior high school students (pubertal), and adults. Twenty-one elementary school children, 18 junior high school students, and 22 adults participated in this study. The maximal strain, stiffness, Young's modulus, hysteresis, and cross-sectional area of the patellar tendon were measured using ultrasonography. No significant difference was observed in the relative length (to thigh length) or cross-sectional area (to body mass(2/3)) of the patellar tendon among the three groups. Stiffness and Young's modulus were significantly lower in elementary school children than in the other groups, while no significant differences were observed between junior high school students and adults. No significant differences were observed in maximal strain or hysteresis among the three groups. These results suggest that the material property (Young's modulus) of the patellar tendons of elementary school children was lower than that of the other groups, whereas that of junior high school students was already similar to that of adults. In addition, no significant differences were observed in the extensibility (maximal strain) or viscosity (hysteresis) of the patellar tendon among the three groups.

No studies have identified the direct effect of changes in cerebral blood flow (CBF) on cognitive function at rest and during exercise. In this study, we manipulated CBF using hypercapnic gas to examine whether an increase in CBF improves cognitive function during prolonged exercise. The speed and the accuracy of cognitive function were assessed using the Stroop color-word test. After the Stroop test at rest, the subjects began exercising on a cycling ergometer in which the workload was increased by 0.5 kilopond every minute until a target heart rate of 140 beats/min was achieved. Then, the subjects continued to cycle at a constant rate for 50 min. At four time points during the exercise (0, 10, 20, 50 min), the subjects performed a Stroop test with and without hypercapnic respiratory gas (2.0% CO2), with a random order of the exposures in the two tests. Despite a decrease in the mean blood flow velocity in the middle cerebral artery (MCA Vmean), the reaction time for the Stroop test gradually decreased during the prolonged exercise without any loss of performance accuracy. In addition, the hypercapnia-induced increase in MCA Vmean produced neither changes in the reaction time nor error in the Stroop test during exercise. These findings suggest that the changes in CBF are unlikely to affect cognitive function during prolonged exercise. Thus, we conclude that improved cognitive function may be due to cerebral neural activation associated with exercise rather than global cerebral circulatory condition.

Background The purpose of this study was to compare the elastic properties and size of tendinous structures and muscle architecture for knee extensors and plantar flexors in boys and men. Methods Twenty-two early pubescent boys (9.6-12.7 yrs) and 23 young adult men (19.8-26.2 yrs) participated in this study. The maximal strain and thickness of tendinous structures for knee extensors and plantar flexors were measured using ultrasonography. In addition, the fascicle lengths of vastus lateralis and medial gastrocnemius muscles were measured. Findings The maximal strain of tendinous structures for plantar flexors was significantly greater in boys than in men, while there was no difference in the maximal strain for knee extensors between the two groups. The relative thickness (to body mass1/3) of Achilles tendon was significantly greater in boys than in men, although there was no difference in that of patellar tendon between the two groups. The relative fascicle length (to limb length) of vastus lateralis muscle was significantly lower in boys than in men, although there was no difference in that of medial gastrocnemius muscle between the two groups. Interpretation These results suggest that the amount of changes in the elastic properties and sizes of tendinous structures and in the fascicle lengths from early pubescence to maturity is different for different muscle groups (in particular, the knee extensors and the plantar flexors). © 2014 Elsevier Ltd. All rights reserved.

In the present study, we aimed to determine whether the advancement in skeletal age (SA) of youth soccer players relative to chronological age was dependent on the maturation spurt or selection bias toward biological maturation. These factors were investigated using cross-sectional and mixed longitudinal study designs. Height, body mass, SA, and maturation differences in 181 youth soccer players (age range; 9.3-16.0 years) were measured. SAs were assessed using the Tanner-Whitehouse three (TW3) and Japanese-standardized SA (J-SA) methods. Thirty-seven of the 181 players (age range; 9.6-13.0 years) then participated in a one-year follow-up study. The participants were divided into seven age groups (under 10 (U10)-U16). Cross-sectional differences in all measurements between the categories were compared with annual increment data. There were significant cross-sectional differences in height (14.9 vs. 10.9±3.3 cm), body mass (13.4 vs. 8.2±3.1 kg), and SA (J-SA: 1.7 vs. 1.0±0.6 yrs; TW3: 2.6 vs. 1.5±0.8 years) between the U12 and U13 groups (p<0.01 each). Furthermore, these differences were higher than those for mixed longitudinal data. These findings imply that advanced biological maturation in youth soccer players may depend on selection bias towards the early biological maturation.<br>

The purpose of this study was to obtain evidence to support the hypothesis that motor unit recruitment is reduced in the quadriceps femoris (QF) of patients with ACL rupture.
We compared muscle torque per unit volume in the QF from injured and uninjured sides to normal subjects. If high-threshold motor unit recruitment is reduced in patients with ACL rupture, this reduction will theoretically lead to a reduction in muscle torque per unit volume compared to the control group. The subjects included 22 patients with ACL rupture and 22 subjects with no history of knee injury. To identify the muscle torque per unit volume, the isokinetic peak torque was divided by QF volume which was obtained by MRI.
Tests revealed that the mean muscle torque per unit volume of the uninjured and injured sides was significantly lower than those of the control group.
This study demonstrated that the values of the muscle torque per unit volume of both injured and uninjured sides of patients with ACL rupture were significantly lower than those of the control group, thereby providing indirect evidence of the hindrance of motor unit recruitment in these patients. The results of the present study also indicate that there may be bilateral QF weakness in patients with ACL rupture. Since persistent QF weakness is a significant barrier to effective rehabilitation in patients with ACL injuries, a better understanding of the underlying mechanisms will allow clinicians and scientists to develop more effective therapeutic strategies for patient rehabilitation.

The aim of the present study was to clarify relationships among the distribution of birth month, maturation and body size in young soccer players. We therefore examined physical and maturational differences between selected players, who were considered to have higher potential to play soccer at a professional level as decided subjectively by coaches, and unselected players. Participants were 332 elite soccer players (mean age 12.2 +/- 1.5 years; range 9.1-15.0 years). Participants were divided into six categories (under - U10 to U15), depending on chronological age. Height, body mass skeletal age and maturation difference (skeletal age - chronological age) were compared among four groups (quarter = Q1 to Q4) depending on month of birth. Overall, the distribution of players across the four quarters was skewed such that numbers were greatest in Q1 and smallest in Q4. No significant differences in maturation difference were observed between birth quarters in any age category. On the other hand, except for the U14 age category, there were no significant differences in height between Q4 and Q1 players. However, the height of Q4 players was significantly smaller than those of Q1 in three (U11, U13 and U14, P &lt; 0.01) of six categories when maturation difference was statistically controlled. Our results suggest a clear bias toward quarter of birth and this bias may depend to some extent on differences in individual skeletal age and body size. Individual biological maturation should thus be considered when selecting adolescent soccer players.

In this study, we examined the relationship between birth-month distribution, skeletal age, height, and weight in adolescent soccer players. The participants were 271 well-trained male adolescent soccer players aged between 9.1 to 15.9 years (N=101 for U12, N=132 for U15, and N=38 for U18). They were divided into four groups according to their month of birth (Q1: Apr-Jun, Q2: Jul-Sep, Q3: Oct-Dec, and Q4: Jan-Mar). Then, the number of players in each group was compared with the standard population of children in Tokyo. Our result showed significant asymmetries in the birth-month distribution for participants of all age groups (p<0.001); it was less than 10% for participants belonging to group Q4. However, no significant difference in maturation ratio (skeletal age-chronological age) was seen among the groups. Moreover, skeletal age did not differ significantly among birth-month for all groups except for Q3. These tendencies were also seen in height and weight distributions. These findings imply that players who biologically mature at an early stage may be selected systematically as soccer players at competitive levels; however, biases based on maturation and physique may cause asymmetric birth-month distribution, as seen in this study.

論文

In this study, the effect of biological maturity in developments of central information processing (CIP) evaluated from choice reaction time (CRT) was investigated from cross-sectional and longitudinal studies. The subjects were Japanese adolescent soccer players. Biological maturity was evaluated according to skeletal age. CRT was measured using the Talent-Diagnose-System. In the cross-sectional study, skeletal age correlated with CRT (r = -0.52, p &lt
0.01), and there were some differences in developmental aspects of CRT between chronological age and skeletal age. In the longitudinal study, CRT improved significantly from 10 to 11 years of chronological age. During this period, development of skeletal age exceeded chronological maturation. Moreover, the annual improvement of CRT correlated with that of skeletal age (r=-0.45, p &lt
0.01). Our results suggest that while we have to consider the effect of external input, such as experience and training, development of CIP was influenced by development of biological maturity in Japanese adolescent soccer players.

KONISHI, Y. Y. SUZUKI, N. HIROSE, and T. FUKUBAYASHI. Effects of Lidocaine into Knee on QF Strength and EMG in Patients with ACL Lesion. Med. Sci. Sports Exerc., Vol. 35, No. 11, pp. 1805-1808, 2003. Purpose: In our previous study, we found that injection of lidocaine into intact knees reduced the maximal voluntary contraction (MVC) and integrated electromyogram (I-EMG) of the quadriceps femoris (QF). This study was designed to investigate changes in the MVC and I-EMG of the QF in response to lidocaine, in patients with anterior cruciate, ligament (ACL) lesion, to evaluate alpha-motoneuron activity innervating the QF. Methods: The MVC of knee extension and I-EMG of the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles were measured in eight patients with ruptured ACL, before and after lidocaine injection into the knee. Results: There were no significant differences between preinjection and postinjection values of MVC (preinjection: 167 +/- 49 N(.)m; postinjection: 164 +/- 55 N(.)m) and I-EMG (preinjection: VL: 0.11 +/- 0.06, VM: 0.13 +/- 0.10, RF: 0.09 +/- 0.04) (postinjection: VL: 0.12 +/- 0.07, VM: 0.13 +/- 0.10, RF: 0.09 +/- 0.05). Conclusion: Our results indicated that hindrance of afferent feedback from the knee in patients with ACL rupture did not significantly change alpha-motoneuron activity. Lidocaine injection into the knee joint of the subjects in this study only attenuated afferent feedback from mechanoreceptors in the knee joint cavity, but not in the ACL. as afferent feedback from ACL was already lost due to ACL rupture. This indicated that attenuation of afferent feedback from mechanoreceptors in the knee joint cavity other than the ACL did not significantly decrease the activity of alpha-motoneurons innervating the QF during MVC exertion. Therefore, our findings provide evidence that afferent feedback from the ACL has a major influence on the MVC exertion of the QF.

The purpose of this study was to clarify the differences in reaction time, stepping frequency and stepping endurance estimated by chronological age compared to skeletal age. The participants were 76 well-trained soccer players aged from 9.7 to 14.8 years old. Height and weight were measured before training. Their skeletal ages were evaluated by RUS score of TW II method. RUS score was calculated for skeletal age by Murata's method. Reaction time, stepping frequency and endurance were measured by Talent-Diagnose-System (Werthner Sports Consulting, KEG, Co, Ltd.) . For chronological age, height increased linearly from 9 to 14. Height estimated by skeletal age increased slowly from 8 to 10, then increased drastically between the ages of 10 to 15. Significant change was shown between the ages of 12 and 13 (p<0.01) . Complex reaction time (CRT) estimated from chronological age developed linearly from 9 to 14 years of age. However for skeletal age, CRT at 10 was slower than at 8 and 9 years of age. Then it developed significantly between the ages of 10 and 11 (p<0.05) . On the other hand, stepping frequency and endurance did not show as remarkable a change with increasing age as reaction time. The results of this present study indicate that in adolescent soccer players, there are some differences between skeletal age and chronological age in cross-sectional change of reaction time. Moreover, skeletal age did not affect the development of stepping frequency and endurance.