Acute Effects of Local High-Frequency Percussive Massage on Deep Fascial and Muscular Stiffness and Joint Range of Motion in Young Adult Men

BACKGROUND

Local high-frequency percussive (HFP) massage has recently found widespread application in physical therapy. Although HFP massage reportedly improves range of motion (ROM), the mechanism underlying its action has not yet been proven. This study aimed to clarify whether a 5-minute percussive massage regimen affects muscular or connective tissues, such as the deep fascia and deep intermuscular fascia and the change in joint ROM.

METHOD

The study sample was calculated using G*Power analysis program, and this study enrolled 15 healthy men who underwent 5-minute HFP massage to the medial gastrocnemius muscle. Shear-wave elastography was used to measure tissue stiffness in the deep fascia, muscle, and deep intermuscular fascia through shear-wave velocity as well as the ROM of the volunteers' ankle joint dorsiflexion before and after the HFP massage. A value of P < .05 was used to declare statistical significance, and post hoc was used to calculate the effect size using G*Power.

RESULTS

Shear-wave velocity revealed a significant change in the deep fascia (P = .003; shear-wave velocity: -0.7 m/s) and significant increase in ROM of ankle dorsiflexion (P = .002; increase in ROM: 3.0°) after 5 minutes of HFP massage. However, the muscle and deep intermuscular fascia did not exhibit any significant changes.

CONCLUSIONS

HFP massage for 5 minutes modified the stiffness of the deep fascia and concurrently improved the ankle joint-dorsiflexion ROM. This method can be used as an intervention to decrease stiffness of the deep fascia and increase the ROM efficiently.

Differences in Lumbopelvic Alignment in Adolescent Male Soccer Players With Bilateral and Unilateral Lumbar Bone Stress Injuries: An MRI Evaluation

Background

Differences in the physical characteristics of bilateral and unilateral lumbar bone stress injuries (BSIs) are unknown.

Purpose

To compare bilateral and unilateral lumbar BSIs in adolescent male soccer players, with a focus on lumbopelvic alignment.

Study Design

Cross-sectional study; Level of evidence, 3.

Methods

A total of 78 players (age range, 12-15 years) from a local soccer club who had magnetic resonance imaging (MRI) evaluations were included in the study. Lumbopelvic alignment and lumbar BSI were evaluated using short-tau inversion recovery and 3-dimensional LAVA on 3-T MRI; lumbar BSI was defined as the presence of bone marrow edema and/or the complete and incomplete fracture in the pars region on the MRI. Pelvic tilt (PT) and pelvic outflare angles were assessed on the kicking and pivoting sides, and asymmetry for each parameter was calculated by subtracting the kicking side from the pivoting side. In addition, the lumbar lordosis (LL), sacral slope (SS), and SS relative to LL (calculated by subtracting LL from the SS) were assessed. One-way analysis of variance was performed to compare lumbopelvic alignment in players with bilateral BSI, unilateral BSI, or no abnormal findings (controls).

Results

No significant differences were found regarding lumbopelvic alignment between the players with bilateral versus unilateral lumbar BSI. PT asymmetry was significantly greater in both players with bilateral lumbar BSI and unilateral lumbar BSI compared with controls (P = .018 and P = .016, respectively). In addition, SS relative to LL was significantly greater in players with bilateral lumbar BSI compared with controls (P < .001).

Conclusion

Although there were no significant lumbopelvic alignment differences between bilateral and unilateral BSI, players with bilateral BSI exhibited increased sacral anterior tilt relative to the LL, and the pelvis was more posterior on the pivoting side than on the kicking side in both players with bilateral BSI and unilateral BSI. Our results suggest that lumbopelvic alignment assessment may contribute to the management strategy for players with lumbar BSI and to the identification of players at high risk of lumbar BSI.

Low Body Fat Percentage and Menstrual Cycle Disorders in Female Elite Adolescent Dancers

Introduction: The menstrual cycle is an important indicator of health in female athletes. Female elite adolescent dancers are expected to control their weight while also training intensely, which can lead to menstrual disorders. This study aimed to investigate the relationship between body composition and menstrual status in female elite adolescent dancers. Methods: In total, 131 female elite adolescent dancers (age: 15.9 ± 1.5 years) were enrolled in this study. We measured the height, weight, and body fat percentage (BFP) for each participant and calculated their body mass index (BMI). We gathered information on individual menstruation patterns and the participants' menstrual cycles over the previous year using recall methods. We then compared the differences between dancers with menstrual cycle disorders and those without. Primary amenorrhea was defined as menarche occurring after the age of 15, while secondary amenorrhe was defined as experiencing fewer than 5 or no menstrual periods for at least 3 of the previous 12 months. We conducted a reliability test using the same questionnaire 2 weeks later. Statistical significance was defined as P < .05, and we calculated the effect sizes (d) and 95% confidence intervals (95% CI). Results: The average BMI and BFP were 22.6 ± 3.0% and 19.4 ± 2.2 kg/m2, respectively. Low BFP and low BMI were observed in 51 (38.6%) and 47 (35.6%) participants, respectively. Primary amenorrhea in 3 participants (2.3%) and 29 (22.1%) reported experiencing secondary amenorrhea; they had lower BFP than the dancers who did not experience amenorrhea (P = .041, 95% CI, -2.51 to -0.05). Conclusion: Female elite adolescent dancers in China may have lower BFP and menstrual problems. Given that lower BFP may contribute to the occurrence of menstruation disorders, it is essential to pay an attention to both BFP and the menstruation status in female elite adolescent dancers.

Are floating toes associated with lifestyle in children? A cross-sectional study

BACKGROUND

Floating toes are a condition and deformity in which some of the toes are afloat. Many functional impairments in floating toes have been previously studied lately and several factors related to floating toes have also been reported. However, no reports have considered the relationship between lifestyle and floating toes among children. The purpose of this study was to reveal the prevalence of floating toes among school children and reveal its relationship with lifestyle.

METHODS

In total, 138 young male baseball players were recruited. Lifestyle was evaluated by using a questionnaire and chosen whether the main lifestyle was Japanese or Western, if the bedding was futons or beds, and if the toilet was Japanese style (a squat toilet) or Western style. Floating toes were defined as toes that were not in contact with the mat. Ankle dorsiflexion in the knee-flexed and knee-extended positions was measured in a weight-bearing position. The relationship between the floating toes and lifestyles, and the comparison of ankle dorsiflexion range of motion between the lifestyles were statistically analyzed.

RESULTS

Players living in a Western style showed a significantly higher prevalence of floating toes on both feet compared with the players living in a Japanese style (throwing side; 39% vs. 19%, p = 0.04, and non-throwing side; 43% vs. 19%, p = 0.01). Players living in a Western style with beds showed a significantly smaller range of motion on both sides of ankle dorsiflexion in the knee-flexed position compared with those who were not (throwing side; 37.2 ± 5.7° vs. 39.0 ± 6.6°, p = 0.04, and non-throwing side; 36.8 ± 5.8° vs. 38.6 ± 6.1°, p = 0.04).

CONCLUSION

Children mainly living in a Western lifestyle showed a significantly higher prevalence of floating toes on both feet compared to those mainly living in a Japanese lifestyle. The prevalence of floating toes may be related to lifestyles among children.

TRIAL REGISTRATION

The study was approved by the institutional review board of the Waseda University Graduate School of Sport Sciences (IRB number 2021-185).

Longitudinal changes in youth baseball batting based on body rotation and separation

BACKGROUND

Identifying the characteristics of batting mechanics, such as the proper angle and position of each body segment in youth baseball players, is important for proper instructions. This study aimed to identify the age-related changes in batting kinematics including rotational and separational movements of the head, upper trunk, pelvis, and arms, in youth baseball players.

METHODS

Over the three seasons, we measured the batting motion of baseball players aged 6- to 12 years using three high-speed cameras. Participants were divided into six age categories according to the little league eligibility rules (players were classified according to their age as of July 31 of a given year). Toss batting was performed using an automatic tossing machine set obliquely in front of the batter. Additionally, we analyzed the rotation angles of the head, upper trunk, pelvis, and arm direction, and the separation angles-calculated using the difference of each rotational angle and the head movement distance and step width-at five points in batting phase: stance, load, foot contact, pre-swing, and ball contact. Finally, 17 players from under 8 (U8, i.e., approximately 7-8 years) to U10 and 13 from U11 to U13 were analyzed. A one-way repeated measures analysis of variance was performed to analyze age-related changes in batting kinematics.

RESULTS

Several age-related changes in batting kinematics at various batting point were observed. The head-to-upper trunk separation angle increased with age from U8 to U10 during the foot contact (effect sizes [ES] = 0.658) and from U11 to U13 during the pre-swing (ES = 0.630). Additionally, the U13 showed a significantly increase in the upper and pelvis separation angles during load, foot contact, and pre-swing compared with U11 and U12 (ES = 0.131, 0.793, and 0.480).

CONCLUSION

Various changes in batting kinematics occurred among each age group. Notably, U12 and U13 had the greater upper trunk-to-pelvis separation angle at foot contact and pre-swing compared to U11. Therefore, it would be important for the instruction of younger baseball players to understand the underdevelopment of trunk separation when batting and encourage the acquisition of such separation movements.

Change in the sub-sesamoid soft tissue thickness under different loading conditions

[Purpose] To measure the sub-sesamoid soft tissue thickness change from non-loading to self-weight loading conditions. [Participants and Methods] The study included 17 female participants for the study. A questionnaire was used to collect the demographic data and participant anamnesis, such as the presence of foot injuries and diabetes. The measured height and weight were used to calculate the body mass index. Participants were required to stand on an evaluation device from non-loading to 100% loading conditions to measure the sub-sesamoid soft tissue thickness. [Results] Significant differences were observed between the tibial and fibular sub-sesamoid soft tissue thicknesses under non-loading and all loading conditions. Significant soft tissue thinning was observed with a change from non-loading to 25% loading condition. However, no significant differences in the rate of change were observed between the tibial and fibular sub-sesamoid soft tissue thicknesses at 100% loading. [Conclusion] The sub-fibular sesamoid soft tissue was thicker than the sub-tibial sesamoid soft tissue in all loading conditions. The sub-sesamoid soft tissue thickness change was larger during initial loading stage than during the late loading stage, which may be normal in healthy females in their 20s.

Characteristics of upper limb mass, muscle CSA and stiffness in adolescent baseball players with and without elbow injury

Since elbow injuries are common in adolescent baseball players, this study aimed to determine the relationship between musculoskeletal status and elbow injuries in 47 baseball players aged 12-14 years. Participants answered a questionnaire and had their general body measurements taken. Magnetic resonance imaging was used to evaluate muscle cross sectional areas (CSA) of the upper arm flexor and extensor muscles, and x-ray absorptiometry was used to determine the mass of the upper arm and the total mass of the forearm and hand. Shear wave elastography was used to determine muscle stiffness of the biceps brachii, brachialis, pronator teres, and brachioradialis. An orthopedic surgeon performed a clinical assessment and elbow ultrasonography for each participant to diagnose elbow injuries. The measured values were compared between the elbow injury and control groups using two-sample t-tests. The elbow injury group had significantly higher muscle stiffness in the brachialis (p < 0.001) and brachioradialis (p = 0.004) muscles and greater elbow flexor CSA of the distal upper arm (p = 0.004) than the control group. The total mass of the forearm and hand and the mass ratio of the forearm and hand to the upper arm were significantly greater in the elbow injury group than in the control group (p = 0.002 and p < 0.001). Thus, it may be necessary to increase flexibility of the brachialis and brachioradialis flexible by stretching and massaging in addition to evaluating the mass distal to the elbow and the elbow flexor muscle size of the distal upper arm to manage elbow injury in youth baseball players. Characteristics of Upper Limb Mass, Muscle Cross-Sectional Area and Stiffness in Adolescent Baseball Players with and without Elbow Injury.

Growth pattern of lumbar maturity stage at L1 to L5 during adolescent growth spurt

PURPOSE

This study aimed to clarify the order of the lumbar maturity stage, each at L1 to L5, and the relationships between age at peak height velocity (APHV) and the lumbar maturity stage.

METHODS

A total of 120 male first-grade junior high school soccer players were enrolled and followed for two years, and measurements were performed five times (T1 to T5). The lumbar maturity stage was assessed according to the degree of lesion of the epiphyseal from L1 to L5 using magnetic resonance imaging and classified into three stages: cartilaginous stage, apophyseal stage, and epiphyseal stage. The relationships between T1 and T5 temporal changes and developmental stages divided by 0.5 year increments based on APHV and the lumbar maturity stage at L1 to L5 were examined. For the apophyseal stage, developmental age calculated based on the difference between APHV and chronological age between each lumbar vertebra was compared.

RESULTS

We found that part of the cartilaginous stages decreased as time progressed, while that of the apophyseal and epiphyseal stages increased at L1 to L5 (chi-square test, p < 0.01). L5 matured earlier with the apophyseal stage than L1 to L4 (p < 0.05). The lumbar maturity stage was attained toward L1 from L5, comparing different lumbar levels.

CONCLUSION

The lumbar maturity stage progresses from L5 toward L1, and the apophyseal and epiphyseal stages would replace the cartilaginous stage at approximately 14 years of age or after APHV.

Risk Factors for Symptomatic Bilateral Lumbar Bone Stress Injury in Adolescent Soccer Players: A Prospective Cohort Study

BACKGROUND

Lumbar bone stress injury (BSI) is a high-risk long time-loss injury for adolescent soccer players. However, the risk factors for lumbar BSI are unclear.

PURPOSE

To identify the risk factors for bilateral lumbar BSI for adolescent soccer players.

STUDY DESIGN

Case-control study; Level of evidence, 3.

METHODS

Adolescent soccer players underwent orthopaedic examination, whole-body dual energy x-ray scan, lumbar magnetic resonance imaging (MRI), and muscle tightness testing at baseline. Lumbar lordosis (LL), sacral slope, maturity stage of lumbar vertebral body, and bone marrow edema (BME) at the L5 were examined via MRI. In addition, bone mineral density and content; trunk lean body mass via dual energy x-ray scan; and bilateral muscle tightness including the iliopsoas, hamstrings, and quadriceps were measured. Lumbar BSI was diagnosed as positive bilateral BME and extension-based lumbar pain. All participants were examined twice, one at 6 months and one at 1 year, after the baseline examination. Multivariate logistic regression analysis was performed to identify the risk factors for bilateral lumbar BSI.

RESULTS

A total of 69 (26.3%) players were diagnosed with bilateral lumbar BSI. Asymptomatic BME (odds ratio [OR], 4.260; 95% CI, 2.153-8.431), apophyseal stage of the lumbar vertebral body (OR, 3.438; 95% CI, 1.698-6.959), sacral slope relative to LL ≥5° (OR, 4.067; 95% CI, 2.021-8.181), and hamstring tightness ≥50° (OR, 3.221; 95% CI, 1.385-7.489) were significantly associated with bilateral lumbar BSI.

CONCLUSION

The incidence of bilateral lumbar BSI was common at 26.2%. Asymptomatic BME, sacral anterior tilt relative to LL, immature lumbar epiphyses, and hamstring tightness were found to be risk factors for bilateral lumbar BSI. The results of this study suggest that regular MRI examination could facilitate the early detection of BME, and improvement in hamstring flexibility and lumbosacral alignment may prevent bilateral lumbar BSI in young athletes.

Ultrasonic Evaluation of the Heel Fat Pad Under Loading Conditions Using a Polymethylpentene Resin Plate: Part 2. Reliability and Agreement Study

Previously, we developed an instrument to evaluate the heel fat pad (HFP) two-layer structure, under varying loading conditions, with ultrasonography from the plantar surface through a polymethylpentene resin plate; the measured values were equivalent to those obtained without this plate. The study described here aimed to determine the intra- and inter-examiner reliabilities of the HFP thickness measurements and the agreement between long- and short-axis measured values using this instrument. Two examiners successively recorded the HFPs of 40 healthy adults twice under the no loading and loading conditions on the long- and short-axis scans. The HFPs were classified into two layers, and their thicknesses were measured. Short-term intra- and inter-examiner reliabilities were determined using the intraclass correlation coefficients. Measurements were repeated 1 mo later to determine the long-term intra-examiner reliability. The agreement between the measured long- and short-axis values was investigated by calculating the minimal detectable changes. The determined short- and long-term intra-examiner reliabilities ranged from 0.750 to 0.999 and from 0.765 to 0.952, respectively. Inter-examiner reliability ranged from 0.765 to 0.997. Differences may occur between the values measured at different axes. The measurements using this evaluation instrument were reliable, and it is best to unify the measurement axis for quantitative research.

The prevalence and effect of the sites of pain in female soccer players with medial shin pain

BACKGROUND

Female soccer players are often diagnosed with medial shin pain, which includes tibial stress fracture, medial tibial stress syndrome, and chronic exertional compartment syndrome. As the possibility of varied sites of pain affecting sports activities has not been fully researched, an urgent discussion and evidence is required. This study investigates the prevalence and effect of sites of pain on the sports activities of female soccer players with medial shin pain.

METHODS

A questionnaire survey was conducted for 196 female soccer players with medial shin pain to assess symptom duration, the effect of practice and performance, and sites of pain. The players were classified into three conditions (tibial stress fracture, medial tibial stress syndrome, or medial shin pain with neurological symptoms) and compared based on sites of pain.

RESULTS

We observed that medial tibial stress syndrome had a lower impact on performance compared to that of tibial stress fracture and medial shin pain with neurological symptoms. While participants with tibial stress fracture had to suspend practice sessions more frequently, the difference in symptom duration between the classified groups was not statistically significant. The effect of sites of pain on sports activities was not significantly different in participants with medial tibial stress syndrome.

CONCLUSIONS

Medial shin pain should be evaluated carefully to differentiate between medial tibial stress syndrome and medial shin pain with neurological symptoms. Restriction of sports activities may help improve the patient's condition early, regardless of the presentation.

Growth until Peak Height Velocity Occurs Rapidly in Early Maturing Adolescent Boys

The timing and tempo of growth rate varies inter-individually during adolescence and can have an impact on athletic performance. This study aimed to determine the difference in growth rate for each maturity status. We combined data collected both retrospectively and prospectively from 78 adolescent boys aged 12 years old; growth charts were collected from their elementary school records, and the height of each participant was subsequently measured every six months over a period of two years. Take Off Age (TOA), Peak Height Velocity Age (PHVA), and Final Height Age (FHA) were estimated using the AUXAL 3.1 program. Growth Tempo 1 and 2 were calculated by dividing the height increase by the time difference between TOA and PHVA, and FHA, respectively. Our results showed three group differences based on the maturation status of PHVA: Growth Tempo 1 and 2 were both higher in the early than during middle and late maturation. Additionally, entering the height at each event as a covariate, the group differences for Growth Tempo 1 did not change; however, for Growth Tempo 2, group differences were eliminated. Therefore, we conclude that during early maturation, growth from TOA to PHVA occurs rapidly and in a shorter period.

The Effect of Foot Deformity and First Metatarsophalangeal Joint Plantar Pain on Performance in DanceSport Athletes

Background: Adolescent DanceSport athletes who regularly dance in high heels have a higher possibility of developing hallux valgus deformity and foot pain. We believe that the occurrence of foot disorders may change the loading on their feet, which thus affects the athletic performance of those adolescents. Methods: A total of 63 adolescent DanceSport athletes (16 boys, 47 girls) were included. The plantar pain in the first metatarsophalangeal (1st MTP) joint was evaluated using a questionnaire, and the hallux valgus angle was evaluated using digital photographs (HVAp). The loading values of the plantar pressure while performing relève on demi-pointe were measured using sensor sheets. The participating boys and girls were analyzed separately. Results: The results showed that female adolescent DanceSport athletes with the 1st MTP joint plantar pain showed a decrease in the loading distribution and plantar pressure percentage on the hallux and an increased loading distribution and pressure distribution of the metatarsal head as the HVAp increased. Conclusion: Among adolescent DanceSport athletes with plantar pain in the 1st MTP joint and a large HVAp, the loading manner of the foot may have changed, which may be associated with a decrease in the toe function and performance.

Ultrasonic Evaluation of the Heel Fat Pad under Weight-Bearing Conditions Using a Polymethylpentene Resin Plate: Part 1

To evaluate the two-layer structure of the heel fat pad (HFP) from non-weight-bearing to full-weight-bearing conditions, we developed an instrument that assesses these changes from the sole through a polymethylpentene resin plate (PMP) with ultrasonography. For actual use, we investigated the influence on measured values and ultrasonogram appearance by interposing the PMP. Additionally, as the PMP may be bent under weight-bearing conditions, its influence on the measured values was investigated. First, two examiners measured the distances inside the phantom with and without a PMP. Second, ultrasonograms were obtained from 40 healthy adults with and without a PMP, and the thicknesses of the whole layer and the two layers of the HFP were measured using the same ultrasonogram. For each experiment, reproducibility was investigated. Third, the distances inside the phantom were measured and compared through the bent PMP, which models the weight-bearing condition, and the flat PMP. The reproducibility of the measurements was equivalent with and without the PMP interposed. Potential bias in measured values arising from deformation of PMP under weight-bearing conditions was not detected. Overall, the PMP's interposition and the bending of the PMP might not influence the measured values and reproducibility of the measurements.

Comparison of foot posture and foot muscle morphology between lifesaver athletes and healthy adults

This study aimed to compare the foot muscle morphology and foot posture between healthy adults and lifesavers in sandy beach sports. The participants included 15 lifesaver athletes and 15 healthy adults. Using a non-contact three-dimensional foot measurement device, the foot length, width, and arch height of the right foot were measured while standing and sitting without back support, and the transverse arch length ratio and arch height index were subsequently calculated. Muscle cross-sectional area was measured using an ultrasound imaging device. Muscle cross-sectional areas, arch height, foot width, arch height index, and transverse arch length ratio were larger in the lifesaver than in the healthy adult group. Lifesavers had higher arches and more developed intrinsic and extrinsic muscles than healthy adults. Performing physical activity while barefoot on sandy beaches may effectively develop the foot intrinsic and extrinsic muscles and raise the arch.

Increase in foot arch asymmetry after full marathon completion

Long-distance running results in lowering of the foot medial longitudinal arch, but it is unknown whether the left and right arches decrease equally. This study aimed to determine whether foot arch asymmetry increases upon completion of a full marathon and to identify factors capable of explaining the degree of asymmetry of navicular height and navicular height displacement. The three-dimensional foot posture data of 74 collegiate runners were obtained using an optical foot scanner system before (PRE) and immediately after (POST) a full marathon. The navicular height and arch height ratio (normalised navicular height by foot length) of both feet significantly decreased from PRE to POST full marathon completion (44.3 ± 6.3 mm versus 40.8 ± 6.5 mm, 17.8 ± 2.5 versus 16.6 ± 2.7, respectively; p < 0.001, both). The asymmetry of the arch height ratio was significantly greater POST than PRE marathon. Multiple linear regression analysis indicated that the POST-race Asymmetry Index (AI) of navicular height was significantly predicted by the PRE-race AI of navicular height; navicular height displacement was predicted by PRE-race navicular height and the marathon time. Full marathon running induced increasing asymmetry and lowering of the medial longitudinal arch in runners.

Identification of physical characteristics associated with swing velocity of batting in youth baseball players

BACKGROUND

Identifying the characteristics of physical function and muscle strength related to swing velocity is necessary for improving batting performance. The purpose of this study was to identify the factors related to swing velocity in youth baseball players.

METHODS

191 youth baseball players aged 7-13 years old participated and were divided into the Tee Ball (˂9.5 years) and Major (≥9.5 years) divisions. We measured the swing velocity for batting performance, medicine ball (MB) back throw and modified star excursion balance test (SEBT) for physical function, and hip muscle torque for lower extremity muscle strength.

RESULTS

Height and MB back throw (β=0.403 and 0.380) for physical function (R2=0.646), and height and internal rotation (IR) torque of the step leg (β=0.620 and 0.216) in lower extremity muscle strength (R2=0.616) were all extracted as related independents for the multiple regression analysis on swing velocity in all subjects. Additionally, height, MB back throw and modified SEBT in the pivot leg (β=0.420, 0.324 and 0.218) for the Major division (R2=0.579), and IR torque of the pivot leg and step leg (β=0.555 and 0.525) for the Tee Ball Division (R2=0.568) were selected.

CONCLUSIONS

Swing velocity was related to height, MB back throws on physical function, and IR torque of the stepping leg in lower extremity muscle strength in youth baseball players. Therefore, the explosive power and strength for stopping the body opposite to the hitting direction are considered necessary to increase the swing velocity.

Optimum Angle of Force Production Temporarily Changes Due to Growth in Male Adolescence

The peak increase in lean mass in adolescents is delayed from peak height velocity (PHV), and muscle flexibility temporarily decreases as bones grow. If the decrease in muscle flexibility is caused by muscle elongation, the relationship between the exerted torque and the joint angle could change in adolescents. The purpose of this study was to investigate the change in the optimum angle of force production due to growth. Eighty-eight healthy boys were recruited for this study. Isokinetic knee extension muscle strength of the dominant leg was recorded. The outcome variable was the knee flexion angle when maximal knee extension torque was produced (optimum angle). The age at which PHV occurred was estimated from subjects’ height history. We calculated the difference between the age at measurement and the expected age of PHV (growth age). A regression analysis was performed with the optimal angle of force exertion as the dependent variable and the growth age as the independent variable. Then, a polynomial formula with the lowest p-value was obtained. A significant cubic regression was obtained between optimum angle and growth age. The results suggest that the optimum angle of force production temporarily changes in male adolescence.

Regional differences in hamstring muscle damage after a marathon

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.