A Longitudinal Study of the Physical Characteristics, Muscle-Tendon Structure Properties, and Skeletal Age in Preadolescent Boys.

OBJECTIVES: The purpose of this study was to examine longitudinal growth changes in physical characteristics, muscle-tendon structure properties, and skeletal age in preadolescent boys and to compare the relationship between the changes in physical characteristics and muscle-tendon properties and the changes in chronological and skeletal ages. METHODS: Fourteen prepubescent boys (10.9 ± 1.1 years old at the onset of the study) participated in this study over two years (yearly). Maximal muscle strength and maximal strain of tendon structure during ramp isometric contraction and muscle and tendon thickness for knee extensors and plantar flexors were measured. In addition, skeletal age was assessed using Tanner-Whitehouse three method. RESULTS: Changes in height, thigh length, and lower leg length were highly correlated with changes in skeletal age but not chronological age. However, changes in the morphological and mechanical properties of muscle and tendon structure were not significantly associated with changes in chronological and skeletal ages. CONCLUSION: The present preliminary results suggest that longitudinal growth changes in the long-axis of the body are highly correlated with skeletal age change, whereas those in the muscle-tendon structure properties were not.

Effect of the FIFA 11+ injury prevention program in collegiate female football players over three consecutive seasons.

This study aimed to investigate the preventive effects of the FIFA 11+ for one-season and over three consecutive seasons on the injury incidence rates in collegiate female football players in terms of duration of intervention. A total of 763 collegiate female football players from seven teams belonging to Kanto University Women Football Association Division 1 in 2013-2015 seasons were included in the study. At the start of the study, 235 players were assigned to a FIFA 11+ intervention group (four teams, 115 players) and a control group (three teams, 120 players). The intervention period was set to three seasons, and the players were followed up during this period. The one-season effect of the FIFA 11+ was investigated after each season. The effect of continuous intervention was verified in 66 and 62 players from the intervention and control groups who continued the study for all three seasons, respectively. The one-season intervention showed significantly lower total, ankle, knee, sprain, ligament injury, noncontact, moderate and severe injury incidence rates in the intervention group in each season. Regarding the continuous intervention, compared with the first season, the injury incidence rates in lower extremity, ankle, and sprain, decreased in the intervention group by 66.0%, 79.8%, and 82.2%, respectively, in the second season, and by 82.6%, 94.6%, and 93.4%, respectively, in the third season, indicating the persistent effect of the FIFA 11+. In conclusion, the FIFA 11+ is an effective program for lower extremity injury prevention in collegiate female football players, and preventive effects persist with continuation of the program.

Risk factors of throwing injuries related to pitching mechanics in young baseball players: a longitudinal cohort study.

BACKGROUND: Risk factors for throwing injuries related to pitching mechanics are unknown. Insufficient pelvic rotation during pitching may be a risk factor for shoulder and elbow injury. This cohort study aimed to identify biomechanics risk factors for throwing injuries in young baseball players. We hypothesized that excessive mechanical load and motion errors would be risk factors for throwing injuries. METHODS: Young baseball pitchers (aged 8-9 years) were recruited from regional baseball leagues between December 2016 and December 2019. Pitching measurements were performed before the start of each season and after the end of the last season in December 2019. The trunk tilt angular displacement, pelvic rotation angular displacement, and forearm rotation angle were calculated using a markerless motion capture system. We also measured elbow varus torque using an accelerometer. After the initial test session, each participant was followed up for 3 years to determine the occurrence of throwing injuries. Players with throwing shoulder and elbow injuries were categorized into the throwing injury group, and those without shoulder and elbow pain for 3 years were categorized into the noninjured group. RESULTS: In this study, 97 baseball pitchers completed a 3-year follow-up. Among those participants, 66 (68.0%) had throwing injuries. A significant difference was observed between the throwing injury and noninjured groups, whereby the injured players had less pelvic rotation angular displacement. CONCLUSION: Insufficient pelvic rotation during pitching is a newly discovered risk factor related to throwing injuries.

Force-Velocity Profiling During the Braking Phase of Countermovement Jump: Relationship to Eccentric Strength and Validity of the 2-Point Method.

ABSTRACT: Nishiumi, D, Yamaguchi, S, Kurokawa, T, Wakamiya, K, and Hirose, N. Force-velocity profiling during the braking phase of countermovement jump: Relationship to eccentric strength and validity of the 2-point method. J Strength Cond Res 37(11): 2141-2148, 2023-The aims of this study were threefold: to investigate the force-velocity profile during the braking phase (bFVP) of the countermovement jump (CMJ) and its relationship with other performance indicators, and whether it could be measured using the two-point method. Sixteen trained men performed 6 different loaded CMJs (0%, 32 kg, 60, 80, 100, and 120% body mass), and eccentric strength measurements were determined. Scatter plots were created using the mean force and velocity during the braking phase of each loaded CMJ. The corrected Akaike's information criterion (AICc) was calculated by fitting linear, quadratic, and cubic regression equations to the bFVP and compared using the 1-way analysis of variance and Bonferroni's post hoc tests. A correlation analysis was performed between the bFVP and other performance indicators. A bias assessment was performed to validate the 2-point method of the bFVP. The significance level was set at p < 0.05. The AICc in the linear regression equation was significantly lower (p < 0.05) than those in the other regression equations. Significant correlations were found between the slope and theoretical maximum force of the bFVP obtained from the linear regression equation and eccentric 1 repetition maximum. The acceptable condition for bias was met by 0-120%. The bFVP is likely to have a linear relationship and can be associated with eccentric strength. Furthermore, the 2-point method in bFVP has validity.

Maturity-Associated Variations in Resistance Exercise-Induced Hormonal Responses in Young Male Athletes.

PURPOSE: To examine differences in resistance exercise-induced hormonal responses among young athletes according to their maturity levels. MATERIALS AND METHODS: A total of 12 collegiate and 32 junior high school male athletes were enrolled. The junior high school participants were divided into pre-peak height velocity (PHV) and post-PHV groups, according to their PHV ages. The salivary testosterone, cortisol, and human growth hormone levels were analyzed before (pre), immediately after (post), and at 15 minutes after performing body weight resistance exercise. RESULTS: The testosterone levels were higher in the collegiate than in the junior high school group (P < .01) and increased after 15 minutes of exercise (P < .01). A significant decrease in the cortisol levels postexercise in the junior high school groups (P < .01) and an increase in the human growth hormone levels at 15 minutes after exercise in the post-PHV group were observed (P < .01). In the collegiate and post-PHV groups, the testosterone-to-cortisol ratio increased post and at 15 minutes after exercise (P < .01). The testosterone-to-cortisol ratio values were higher in the collegiate than in the post-PHV (at preexercise and at 15 min after [P < .01]) and pre-PHV groups (at all times [P < .01]). CONCLUSION: Exercise-induced acute hormonal responses to resistance exercise may depend on individuals' maturity levels, even in those having the same age.

Neuromuscular responses of the hamstring and lumbopelvic muscles during unanticipated trunk perturbations.

Hamstring strain often occurs when an opponent unanticipatedly perturbs an athlete's movements. We examined the neuromuscular responses of hamstring and trunk muscles during unanticipated trunk perturbations in athletes with and without a history of hamstring strain injury. Male college athletes (11 with a history of a unilateral hamstring injury and 10 without prior injury) knelt while wearing a chest harness attached to a cable that was pulled backward. They were instructed to resist the force isometrically and maintain their position when the perturbations were applied. The pressure was released with or without a cue (CUE or NoCUE). We measured trunk acceleration, three-dimensional kinematic data, and surface electromyography (EMG) signals of the erector spinae, internal oblique, gluteus maximus, biceps femoris long head, and semitendinosus muscles. Maximum trunk acceleration and displacement were greater with NoCUE in both groups (p < 0.05). EMG amplitude did not differ after perturbation of any investigated muscle. The injured group demonstrated a delayed onset of the gluteus maximus and erector spinae muscles in NoCUE versus CUE stimuli (p < 0.05). Athletes with a history of hamstring strain injury exhibited a reduced neuromuscular coordination of the lumbopelvic muscles in response to unanticipated trunk movement.

Acceleration Profile of High-Intensity Movements in Basketball Games.

ABSTRACT: 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 36(6): 1715-1719, 2022-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.

Difference of Hamstring Activity Between Bilateral and Unilateral Nordic Hamstring Exercises With a Sloped Platform.

CONTEXT: 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. DESIGN: This study was designed as a case-control study. METHODS: 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. RESULTS: The BFlh %MVIC was significantly higher in N40U (P < .05) and N50U (P < .05) than in N40. A significant difference in BFlh %MVIC and ST %MVIC was observed between N40U (P < .05) and N50U (P < .05). The mean values of BPA and the angle at peak BFlh EMG were <30° for all NHE variations. CONCLUSIONS: 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.

Effects of Self-myofascial Release Using a Foam Roller on Range of Motion and Morphological Changes in Muscle: A Crossover Study.

ABSTRACT: 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 35(9): 2444-2450, 2021-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.

Biceps Femoris Muscle is Activated by Performing Nordic Hamstring Exercise at a Shallow Knee Flexion Angle.

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 < 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.

Effects of an Injury Prevention Program on Anterior Cruciate Ligament Injury Risk Factors in Adolescent Females at Different Stages of Maturation.

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 post-pubertal 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.

Effect of Different Slopes of the Lower Leg during the Nordic Hamstring Exercise on Hamstring Electromyography Activity.

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° (NH), 20° (N20), and 40° (N40). To compare hamstring EMG activity during the NHE variations, the knee flexion angle was set in the range from 0° to 50°, divided into five phases (0-10°, 10-20°, 20-30°, 30-40° and 40-50°), where 0° 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°/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° (p < 0.05). For the BPA, NH (57.75° ± 13.28°), N20 (36.27° ± 9.89°) and N40 (16.26° ± 9.58°) 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.

Immediate effects of plantar vibration stimuli during static upright posture following total hip arthroplasty in females.

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.

Fear Avoidance Beliefs in College Athletes with a History of Ankle Sprain.

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).

Relationship Among Biological Maturation, Physical Characteristics, and Motor Abilities in Youth Elite Soccer Players.

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.

Effects of Self-Massage Using a Foam Roller on Ankle Range of Motion and Gastrocnemius Fascicle Length and Muscle Hardness: A Pilot Study.

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°), 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° [8.0°], POST: 16.6° [8.4°]; P < .001), although plantar flexion ROM did not change significantly between PRE and POST (PRE: 40.0° [6.1°], POST: 41.1° [4.9°]). 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.

Influence of Altered Knee Angle and Muscular Contraction Type on Electromyographic Activity of Hamstring Muscles during 45° Hip Extension Exercise.

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.

Hamstring muscles' function deficit during overground sprinting in track and field athletes with a history of strain injury.

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.

Longitudinal Age-Related Morphological and Physiological Changes in Adolescent Male Basketball Players.

This study aimed to examine longitudinal age-related changes in muscle morphology and jump and sprint performances of youth athletes. The subjects of this longitudinal study were 41 youth male basketball players who were assigned to late, mid, and early groups based on differences regarding the estimated age at peak height velocity. The vastus medialis, vastus intermedius, rectus femoris, vastus lateralis, biceps brachii, and triceps brachii thicknesses were assessed using ultrasonography. The subjects' anaerobic capacities were evaluated based on Abalakov jumps and 20-m sprint time. After 1 year, the vastus medialis and biceps brachii thicknesses increased significantly in all groups, and the rectus femoris, vastus intermedius, and vastus lateralis thicknesses increased significantly in the late and mid groups, but not in the early group. The Abalakov jumps and 20-m sprint time improved significantly in all groups. The early group's 10-m sprint time improved significantly. Cross-sectional comparisons showed that after 1 year, the early group's Abalakov jumps and 20-m sprint time at baseline, its Abalakov jumps, and 10-m and 20-m sprint times were significantly better than those in the mid and late groups. Hence, significant muscle growth occurred before the athletes reached the age at peak height velocity. During puberty, late maturers' sprint times and jump performances may not catch up with those of early maturers. The speed and tempo of the morphological growth and anaerobic ability of athletes in the same age category depend on athletes' biological maturity.

Kerlan-Jobe Orthopaedic Clinic (KJOC) score and scapular dyskinesis test in collegiate baseball players.

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.