BACKGROUND: Low-frequency acupuncture is used to maintain skeletal muscle flexibility and improve joint range of motion; however, its definite effects are unclear. This study aimed to determine the effects of low-frequency acupuncture on muscle and fascial stiffness and ankle dorsiflexion range of motion. METHODS: The participants included 12 randomly selected healthy adults. The medial head of the gastrocnemius muscle was selected as the target muscle, and changes in hardness and dorsiflexion range of motion of the ankle joint in the deep fascia, muscle, and deep intermuscular fascia of the same region were measured before and after low-frequency acupuncture intervention. Acupuncture needles were inserted until they passed through the deep intermuscular fascia and electrically stimulated at a frequency of 2 Hz for 15 min. The 12 right legs were the intervention legs, and the 12 left legs were the non-intervention legs. RESULTS: In the intervention leg, hardness increased in the deep fascia immediately after low-frequency acupuncture, but decreased in all regions (deep fascia, muscle, and deep intermuscular fascia) after 15 min. The rate of change in hardness was the greatest in the muscles and deep intermuscular fascia. Additionally, the ankle's dorsiflexion range of motion increased after 15 min. In contrast, the non-intervention leg showed no significant changes in stiffness or ankle dorsiflexion angle. CONCLUSIONS: Low-frequency acupuncture may decrease muscle stiffness and improve fascial gliding. The change in hardness tended to be greater in the deeper areas.

INTRODUCTION: To the best of our knowledge, no previous studies have linked the progression of hallux valgus (HV) with plantar pressure distribution. Therefore, this study aimed to determine the progression of HV angle in elite adolescent dancers and evaluate the risk factors associated with foot plantar pressure during demi-pointe movement. METHODS: For this cohort study, 40 adolescent dancesport dancers (age: 14.5 ± 1.3 years; height: 168.3 ± 8.3 cm; weight: 52.4 ± 8.1 kg) were recruited from a dancesport specialty school. All participants reported no foot or lower limb injuries or symptoms in the past year and were not undergoing any rehabilitation or medication treatment. The HV angle was measured by photography (HVAp). The HVAp survey included baseline and follow-up assessments after 1 year. Foot plantar pressures (kPa) were obtained using the F-Scan measurement system (Tekscan, Tokyo, Japan), and the data were divided into two categories based on the foot location (type 1: hallux, toe, and metatarsophalangeal [MTP] joint area and type 2: medial, middle, and lateral areas). Data were analyzed using the Pearson's chi-square test and multiple logistic regression. RESULTS: The HVAp measurement demonstrated excellent reliability. A significant increase of 2.1° ± 3.5° in the HV angle of elite adolescent dancers was found at the 1-year follow-up assessment relative to that at baseline. There were significant correlations between the HVAp variation values and the hallux (r = - 0.480, P = 0.002), toe (r = - 0.313, P = 0.049), and MTP joint area (r = 0.446, P = 0.004) plantar pressure percentages in the type 1 category and medial area (r = - 0.331, P = 0.037) and middle area (r = 0.386, P = 0.014) pressure percentages in the type 2 category. Based on the multivariate logistic regression analysis, the HVAp variation values were associated with foot plantar pressure in the hallux (odds ratio [OR]: - 0.12, 95% confidence interval [CI]: - 0.191 to - 0.048, P = 0.002) and middle areas (OR: 0.09, 95% CI: 0.019 - 0.161, and P = 0.014) from the two categories, respectively. CONCLUSION: This study demonstrated significant progression of the HV angle in elite adolescent dancers over 1 year, which was significantly associated with increased foot plantar pressure in the middle area and decreased plantar pressure in the hallux area. These findings highlight the importance of monitoring and addressing foot plantar pressure in adolescent dancers.

This study aimed to evaluate developmental patterns in athletic performance during youth and determine their association with changes in physical fitness. The testing included three athletic performance (i.e. ball speed in pitching, swing velocity in batting, 30-metre sprint time) and two physical fitness tests (i.e. medicine ball [MB] back throw and modified star excursion balance test [SEBT]). Data from 235 players (557 measurements) aged 6 to 14 were eligible for a longitudinal evaluation. The statistical analysis was based on the latent growth curve models of the athletic performance development process and the random-effect panel data multivariate regression analysis for ball speed, swing velocity, and 30-metre sprint time. The 30-metre sprint time showed a small curvature but an accelerated increase around 12‒13 years old. However, the ball speed, swing velocity, and modified SEBT demonstrated a slower or less accelerated change in the developmental pattern starting around 12‒13 years old. Multivariate longitudinal analysis revealed that developmental change in athletic performance was positively associated with age and MB back throw. Our findings highlight the developmental patterns of athletic performance associated with baseball exhibiting stagnation as well as acceleration, which may help develop effective age-appropriate strategies for improving performance in youth baseball players.

BACKGROUND: Sports injuries often occur during landing, necessitating postural stability for injury prevention. Electrical stimulation of the plantar foot induces activities of the intrinsic foot muscles and improves somatosensory and postural stability during landing. However, this effect remains unclear. Therefore, the aim of this study was to investigate the immediate effects of electrical stimulation on the activities of the intrinsic foot muscles, plantar somatosensory system, and postural stability during landing. METHODS: Twenty-two college athletes were divided into an electrical stimulation group and a control group. Electrical stimulation was applied to the plantar foot using a commercial device. The toe function and plantar tactile sensations were evaluated. The activities of the intrinsic muscles and the parameters of the ground reaction force were measured and calculated. We compared pre- and postintervention outcomes. RESULTS: In the electrical stimulation group, two subjects showed improvement in toe function, and plantar tactile sensation improved significantly postintervention. The control group exhibited no significant change in plantar tactile sensation. A significant interaction was observed in anteroposterior postural stability during landing, notably improving in the electrical stimulation group. CONCLUSIONS: Electrical stimulation of the plantar foot immediately improved toe function, plantar tactile sensation, and postural stability during landing. Such stimulation would be beneficial in preventing sports injuries.

BACKGROUND: Growth-specific physical characteristics in adolescence may mediate throwing-related loads and movement patterns associated with elbow injuries. In a previous study, the authors calculated the forearm-hand inertia, which is the moment of inertia centered at the elbow joint. PURPOSE: To determine the relationship of forearm-hand inertia values with throwing motion patterns and elbow valgus load in adolescent baseball players. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 35 adolescent baseball players underwent measurements by dual-energy x-ray absorptiometry (DXA) scans and a throwing trial. Forearm-hand inertia was determined as the joint moment around the elbow using the subregion analysis mode of DXA. Elbow valgus torque and ball speed during throwing were measured using a dedicated sensor and speed gun, and throwing efficiency was calculated by dividing the elbow valgus load by the ball speed. Players were divided according to the throwing motion pattern in which maximum acceleration occurred: pelvis-upper arm-forearm (proximal-to-distal sequencing [PDS] group; n = 19) or pelvis-forearm-upper arm (proximal upper extremity [PUE] group; n = 16). The groups were compared in terms of ball speed, elbow valgus torque, throwing efficiency, and forearm-hand inertia using t tests and analysis of covariance, with forearm-hand inertia as covariates. The chi-square test was used to examine the relationship between throwing motion patterns and forearm-hand inertia. RESULTS: The PUE group had a higher elbow valgus load (effect size [ES] = 0.65; P = .03), throwing efficiency (ES = 0.63; P = .02), and forearm-hand inertia values (ES = 0.64; P = .04) than the PDS group. In addition, a significant relationship was observed with throwing patterns when forearm-hand inertia values were 350 kg·m2 (OR, 2.36; 95% CI, 1.09-5.12; P = .012) and 400 kg·m2 (OR, 1.68; 95% CI, 0.99-2.85; P = .037). CONCLUSION: Study results indicated that growth-specific physical characteristics in adolescent baseball players exhibited in forearm-hand inertia mediated the relationship between high elbow valgus and poor throwing efficiency caused by poor throwing motion patterns. CLINICAL RELEVANCE: A better understanding of the details in muscle function with throwing mechanics may prevent future injuries.

BACKGROUND: This study aimed to determine the risk factors of hallux valgus angle among preprofessional adolescent dancesport athletes. METHODS: A total of 275 athletes, (73 males and 202 females) aged between the ages of 11 and 18 years, participated in this study. A cross-sectional questionnaire was used to survey their demographic characteristics (sex and age), training information (starting age, weekly training time, and athletic career [number of years of training at this specific dancesport school]), and measured their height and weight. The hallux valgus angle was measured based on foot photographs. The chi-square test was used to compare the difference with prevalence of hallux valgus between male and female athletes. A normal distribution test was performed, and based on the test results, unpaired t-test and multiple logistic regression were conducted to identify training factors for the hallux valgus in this cohort. RESULTS: Chi-square test showed higher prevalence of hallux valgus in female elite adolescent dancesport athletes than males. The t-test results did not show any significant differences between the hallux valgus group and non-hallux valgus groups with start age, athletic career, and weekly training time. Multiple logistic regression analysis with hallux valgus as the dependent variable revealed that the female sex was a strong predictor of a higher prevalence of hallux valgus (odds ratio [OR]: 3.954, 95% confidence interval 95% CI: 2.193-7.131, and p < 0.001). Weekly training time was also entered into the multiple logistic regression model (OR: 1.033, 95% CI: 1.001-1.067, and p = 0.041). CONCLUSIONS: Our findings revealed that the prevalence of hallux valgus in adolescent dancesport athletes was higher in females than in males. Longer weekly training time was also a risk factor for hallux valgus. Training factors should be considered in preventive programs for elite adolescent dancesport athletes, and special attention should be paid to female athletes.

Activities on sandy soil are known to contribute to improved leg strength and balance. Lifesavers (LSs) have shown that sandy soil activity promotes intrinsic foot muscle development and improves balance. LS improves leg strength and balance through activities on sandy soil. However, the effect of foot muscle development on the actual muscle activity of LS remains unclear. We aimed to evaluate the effect of foot muscle development on muscle activity in lifeguards on a sandy beach compared with the corresponding in healthy participants. Fifteen LSs and 15 healthy adults underwent a Y-balance test to assess dynamic balance and surface electromyography to measure muscle activity. The LSs exhibited a significantly higher percentage of maximum voluntary contraction values in the tibialis anterior muscle in all directions than the healthy adults. The LSs showed increased peroneus longus and abductor hallucis muscle activity in the posterolateral and posteromedial directions, suggesting their involvement in contralateral postural control during dynamic balance. These findings suggest that engaging in barefoot activities on sandy soil enhances foot muscle activity and improves dynamic balance in LSs.

BACKGROUND: This study aimed to investigate age-related changes in the heel fat pad's microchamber and macrochamber layers, particularly focusing on load-induced alterations. Understanding these changes is crucial for elucidating age-related differences in foot mechanics and their potential implications for mobility and comfort. METHODS: Fifty-five healthy individuals were divided into three age groups: young adults (≤29 years), middle-aged adults (30-44 years), and elderly individuals (≥45 years). Ultrasonic imaging was utilized to measure the thickness of the heel fat pad's microchamber and macrochamber layers under varying load conditions. Thickness, percentage changes, and ratios of load-induced thickness changes were calculated to assess age-related differences. FINDINGS: Under no-load conditions, both microchamber and macrochamber layers of the heel fat pad were significantly thicker in middle-aged and elderly individuals than in young adults. When load was applied middle-aged and elderly participants exhibited smaller changes in the macrochamber layer and larger changes in the microchamber layer compared to young adults. INTERPRETATION: Our findings suggest that age influences the structural characteristics and response of the heel fat pad to mechanical loading. Thicker heel fat pad layers in middle-aged and elderly individuals under no-load conditions may reflect age-related changes in fat distribution or composition. Moreover, differences in load-induced thickness changes indicate altered mechanical properties with age, potentially affecting shock absorption and overall foot function. Understanding these age-related variations can help develop interventions aimed at preserving foot health and mobility across the lifespan.

Toe flexor strength is generated primarily by the flexor hallucis longus (FHL) of the extrinsic foot muscles (EFMs) and the plantar intrinsic foot muscles (PIFMs) of the great toe. Toe flexion methods can be broadly classified into toe grip (TG) and toe push-down (TP). Additionally, TP's interphalangeal joint (IPJ) position may influence the FHL and PIFMs activity ratios. This study aimed to elucidate the differences in the muscle activity and muscle activity ratios of the FHL and AbdH during TG, TP with IPJ flexion (TPIF), and TP with IPJ extension (TPIE). Surface electromyography and a custom-made instrument were used to measure the FHL and AbdH muscle activity during TG, TPIF, and TPIE of the great toe in 28 healthy men. The muscle activity and AbdH/FHL muscle activity ratio in the three conditions were statistically compared. The FHL activity was significantly higher during TG and TPIF than during TPIE. The AbdH muscle activity was significantly higher during TPIF and TPIE than that during TG. The AbdH/FHL muscle activity ratio was significantly higher for TPIE, TPIF, and TG in that order. This study showed that the FHL and AbdH muscle activity differed depending on the TG and TP of the great toe, and that the AbdH/FHL muscle activity ratio was different in the IPJ position. These results suggest that selecting a toe flexion method according to the target muscle when measuring and training the great toe flexor strength is important.

Prevalence of impaired foot function among baseball players with and without a disabled throwing shoulder/elbow was investigated. The study included 138 male players. Players who had previously complained of shoulder/elbow pain during throwing motion were defined as the players with a history, and those who experienced shoulder/elbow pain during the examination were defined as having the injury. Foot function was evaluated by foot "rock paper scissors" movements and floating toes. Their prevalence was assessed and the relationships between players with and without the injuries were statistically analyzed. The prevalence of players with a history and injury was 27% and 7%, respectively. The prevalence of impaired foot function on the non-throwing side among players with injury was significantly higher than those without (60% vs. 28%, P < 0.001) and higher tendency on the throwing side than those without (60% vs. 32%). Regarding floating toes, players with a relevant history showed a significantly higher prevalence on the throwing side than those without (49% vs 28%, P < 0.001) and higher tendency on the non-throwing side than those without (49% vs 32%). Players with disabled throwing shoulder/elbow have a significantly higher prevalence of impaired foot function and floating toes than players without it.

本研究の目的は発育段階にある野球選手を対象に、投球側の上肢各分節の骨長、骨量(BMC)、骨密度(BMD)の投球側・非投球側の違いを明らかにすることとした。野球を始めて1年以上経過している中学生の男子野球選手49名を対象に、DXA装置を用いた全身スキャンを行った。その後SubRegion機能を用いて上肢を上腕部、前腕部、手部に分画し、それぞれの骨長、BMC、BMDを算出した。投球側と非投球側の比較にはt検定を、分節ごとのBMCおよびBMDと骨長との関係については単変量の線形回帰分析を投球側と非投球側に分けて実施した。投球側の上腕部および前腕部のBMC、上肢各分節のBMDは非投球側と比較して有意に高値を示した(いずれもp<0.001)。一方で上肢各分節長は投球側と非投球側との間に有意な差は認められなかった。また、上肢各分節のBMCおよびBMDと骨長との関係は投球側・非投球側を問わず、すべての組み合わせにおいて有意な関連が認められた(p<0.001)。なお、上腕部のBMCと上腕長との関係については投球側と非投球側との間に有意な交互作用が確認され、回帰式の傾きに差があることが示された。投球の反復によって上肢各分節の骨量獲得が促進されることが明らかとなった。投球側の上腕部のBMCは非投球側よりも上腕長との関係が強かったものの、上肢各分節長は投球側と非投球側で違いがなかったことを踏まえると、野球選手のBMCの獲得には上腕骨の短軸方向の発育への影響が関連する可能性が示唆された。(著者抄録)

BACKGROUND: This study aimed to investigate the thickness changes of the heel fat pad and the plantar fascia associated with loading and unloading in healthy individuals and patients with heel pain and reveal the differences between them. METHODS: The study included adult male participants with (n = 9) and without (n = 26) heel pain. The participants placed their right foot on an evaluation apparatus with a polymethylpentene resin board (PMP), while their left foot was positioned on a weighing scale used to adjust the loading weight. The heel fat pad was differentiated into superficial Microchamber and deep Macrochamber layers. These layers and plantar fascia thickness were measured using an ultrasonographic imaging device at loading phase ranging from 0% to 100% of their body weight and unloading phase from 100% to 0%. Additionally, the study examined the thickness change ratios of the superficial and deep heel fat pad layers when the load increased from 0% (unload) to 100% (full load). RESULTS: In healthy individuals and patients with heel pain, no significant thickness changes were observed in the Microchamber layer of the heel fat pad or the plantar fascia during loading and unloading evaluations. However, significant thickness changes were observed in the Macrochamber layer of the heel fat pad, and the pattern of change differed between the loading and unloading phases. Additionally, patients with heel pain showed differences in the thickness change and thickness change ratios of the microchamber and macrochamber layers of the heel fat pad during both loading and unloading phases. The thickness of the plantar fascia did not show significant differences between both groups. CONCLUSION: Compared with healthy individuals, in our relatively small study, patients with heel pain had greater deep fat pad compression in loading and less recovery after load removal. This finding suggests that these patients have different intrinsic fat pad function and related morphology than those without heel pain. LEVEL OF EVIDENCE: Level III, retrospective cohort study.

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 &lt; .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.

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.

INTRODUCTION: This study examined the relationship between ball release points and pitching performance among professional baseball pitchers, with a focus on variability. METHODS: We used open-source data to compare ball release point variability between Major League Baseball (MLB) and Minor League Baseball (MiLB) players. The relationship between pitching performance and variability was analyzed using multiple regression analysis. RESULTS: MLB players exhibited smaller ball release point variability compared to MiLB players. The analysis showed that pitching performance was strongly related to ball release point variability, especially in the horizontal direction on the coronal plane. Horizontal ball release point variability was most strongly related to strikeout ability among pitching performances. DISCUSSION: These results suggest that reducing horizontal ball release point variability may improve pitching performance, particularly by increasing strikeouts and reducing home runs allowed. This study provides a data-driven approach to understanding the mechanics of pitching and can be applied to the development of advanced training methods and technical solutions aimed at improving pitching performance in baseball players.

慢性足関節不安定症(CAI)では,足関節の関節位置覚や足底表在感覚の低下といった固有受容感覚の低下が報告されている.これらの固有受容感覚の低下に対して,足底振動刺激の有効性が期待されているものの,その効果は不明な点が多い.そこで本研究では,健常アスリートおよびCAIを有するアスリートに対する,足底振動刺激が足関節関節位置覚および足底表在感覚に与える即時効果を明らかにすることを目的とした.対象は健常群8名,CAI群8名とし,介入前後での関節位置覚および足底表在感覚を測定した,介入は足底振動刺激実施条件または安静条件とし,crossover試験を行った.関節位置覚は底屈,内がえしの2方向を測定し,足底表在感覚は第1中足骨頭,第5中足骨底,踵部の3項目を測定した.関節位置覚,足底表在感覚ともに健常群とCAI群の間に有意な差を認めなかった.また条件に関わらず両群とも介入前後において有意な変化を認めなかった.健常群とCAI群に差を認めなかった要因の一つとして,CAI群におけるFAAMスコアが高かったことが考えられる.また健常群とCAI群ともに振動刺激後に関節位置覚と足底表在感覚に変化を認めなかった.振動刺激の周波数や振幅が,先行研究より小さかったことや,CAI群の関節位置覚や足底表在感覚が健常群と同程度であったことが要因として考えられる.今後,介入条件や異なる対象への介入を検証する必要がある.(著者抄録)

足関節捻挫の治療やその再発予防のために使用されている薄型足関節捻挫用サポーターは足関節の底背屈可動域を制限する可能性がある.また,運動によりその制限は更に低下する可能性があるが,現時点ではこれらに関しては不明である.本研究の目的は,薄型足関節捻挫用サポーターの装着による足関節底屈および背屈可動域制限の有無および運動による影響の有無を検討することである.対象は,一般成人男性5名,平均年齢は30.8±5.2歳である.足関節背屈と底屈の自動および他動可動域を,それぞれ膝関節伸展位と屈曲位で裸足とサポーター装着下で計測した.運動課題は,カーフレイズ,フルスクワット,垂直ジャンプ,ランニングとし,サポーター装着下各運動課題後に同様の可動域を計測した.全ての条件で3回計測し平均値を算出後,裸足とサポーター装着下,サポーター装着下での運動課題前後の可動域を対応のあるt検定で統計学的に解析した.その結果,裸足とサポーター装着下では全ての計測項目で有意な変化はなかった.また,各運動課題前後においても全ての計測項目で有意な変化はなかった.本研究の結果,薄型足関節捻挫用サポーターは足関節の底屈および背屈可動域を制限しない可能性がある.(著者抄録)

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).

Abstract

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.

本研究は小学生から高校生までの野球選手を対象に、上腕骨幅の発育変化を明らかにすることを目的に実施された。8歳から18歳までの野球選手124名を対象に、DXA装置を用いた全身スキャンを行った。そして画像解析ソフトを用いて上腕骨の中央部、遠位25%、近位25%における上腕骨幅を、投球側および非投球側それぞれで算出した。そして上腕骨幅の発育変化を明らかにするため、上腕骨中央部、遠位25%、近位25%の骨幅と暦年齢との関係を平滑化スプラインでフィッティングさせた。また、上腕骨中央部の骨幅と骨長との関連を単変量の回帰分析を実施し、共分散分析を用いて2群間の回帰の平行性を調べた。非投球側の近位25%における上腕骨幅と暦年齢との関係を除き、全ての関係において平滑化スプラインモデルが線形回帰モデルよりもあてはまりが良かった(p<0.05)。上腕骨幅の発育変化について、上腕骨中央部の骨幅は15歳から16歳頃に変化が横ばいになること、近位および遠位25%の骨幅は投球側が非投球側と比較して12歳以降に変化が急激になることが示された。上腕骨中央部の骨幅と上腕骨長との関係は投球側、非投球側ともに有意な関連が認められた(R2=0.474、p<0.001、R2=0.486、p<0.001)。投球側の上腕骨中央部の骨幅は非投球側と比較して有意に高値を示し、2群間に回帰の平行性が確認されことから、投球側の上腕骨中央部の骨幅は上腕骨長に依存せず非投球側より高値を示すことが明らかとなった。(著者抄録)

(目的)Magnetic resonance imaging(MRI)を用いた仙骨傾斜角評価を基準とし,傾斜計を用いた腰仙椎角の計測の精度を検証とすること,予測回帰式を探索することを目的とした.(方法)中学生の男子70名を対象とし,腰部のMR撮像および傾斜計を用いた腰仙椎アライメント測定を実施した.得られたMR画像から脊柱の正中矢状断を抽出し,仙骨の上縁と画像の水平線をなす角を仙骨傾斜角として算出した.また,腰仙椎角の測定には傾斜計を用い,腰仙椎部に傾斜計の0°の軸が通る位置で計測を行った.そしてBland-Altmanプロットを用いた両測定法の一致度の検証に加え,MR撮像による仙骨傾斜角と傾斜計による腰仙椎角との関係を線形回帰分析によって検討した.(結果)MRIを用いた仙骨傾斜角と傾斜計による腰仙椎角との差で求められる固定誤差は10.06±3.29°を示した一方で,比較誤差および偶然誤差は小さかった.MRIを用いた仙骨傾斜角と傾斜計による腰仙椎角との間には有意な関連が見られ,予測回帰式はy=0.85x+13.49が得られた.(結論)傾斜計を用いた腰仙椎角の評価はMRIを用いた仙骨傾斜角と比べて計測値が過小評価されやすい可能性がある.しかしながら比例および偶然誤差は小さく,傾斜計で得られる数値を基に仙骨傾斜角の予測が可能となると考える.(著者抄録)

本研究の目的は中学生の側腹部筋厚全体の筋厚の発育様式と外腹斜筋(external oblique;EO),内腹斜筋(internal oblique;IO),腹横筋(transversus abdominis;TrA)の個別の筋厚の発育様式の違いを明らかにすることを目的とした.対象は地域クラブチームに所属する中学生191名で,超音波画像診断装置を用いて右側のEO,IO,TrAの筋厚を測定した.身長で5cmごとの階級に分類し,身長(x)と側腹部筋(y)のアロメトリー式y=bxaを算出した.その後直線式を算出し両者が複数の直線で表される場合,隣接する直線の交点を変移点とした.変移点はアロメトリー係数aの値が1以上変化した点とした.側腹部筋のアロメトリー係数aは1つの変移点をもつ2相の直線で表され,それぞれアロメトリー係数aは1.28,3.42で変移点は168.8cmであった.EOとIOは2つの変移点をもつ3本の直線で表され,EOのアロメトリー係数aは2.58,1.56,2.76で変移点は142.0cm,171.3cmとなった.IOは0.82,2.05,4.55で変移点は157.4cm,170.4cmとなった.TrAは1つの変移点をもつ2本の直線で表され,-1.53,1.56で変移点は145.3cmとなった.このことから,体幹を安定させる作用をもつTrAは早期に発育することが考えられた.(著者抄録)

[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.

足半(あしなか)は,踵が地面に直接触れる前足部のみの草鞋であり,現代では,足底感覚や足趾屈曲筋力の向上を期待されている.本研究は,短時間の足半着用歩行が足趾屈曲筋力へ及ぼす影響を明らかにすることを目的とした.対象者は足半着用経験のない一般男性7名とし,足半着用とスニーカー着用において5分間の歩行課題(日常生活歩行速度)を行った.各歩行課題実施前後に母趾屈曲筋力と第2～5趾屈曲筋力をハンドヘルドダイナモメーターにて測定した.足半のみ歩行課題実施前後で母趾屈曲筋力が上昇した.足半歩行では,足趾で鼻緒を挟み,足半の先端を覆うように把持するため,足趾屈曲に関与する筋を促通させる可能性が示唆された.(著者抄録)

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.

バスケットボールにおける足関節捻挫要因である,ポジション(ガード,フォワード,センター),受傷場面(試合,練習),受傷機転(接触の有無及び接触部位(足・足関節部,足・足関節部以外))の3点を複合的に検討し,足関節捻挫発生率との関連性を明らかにするために,大学女子バスケットボール選手延べ60名を対象に3シーズン33ヵ月の疫学調査を行った.単一因子での検討では,Forward,試合時,足部同士の接触による発生率がそれぞれ最も高かった.複数因子での検討では,Guardで試合時の足部同士の接触による発生率が最も高かった.単一因子と複数因子の検討間で結果に差異があることから,単一因子ではなく,複数因子によるより詳細な検討の必要性が明らかとなった.(著者抄録)

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.

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.

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.

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.

【目的】中学生野球選手における投球障害肩の既往が上肢分節重量および肩甲帯除脂肪量に与える影響を明らかにすることを目的とした。【方法】対象は中学1〜3年生の野球選手149名とし、その内16名をInjured Shoulder群、133名をNon Injured群に分類し、比較検討を行った。測定はDXA装置を用い、whole body modeを用いて全身スキャンを行った。そしてSubRegion機能を用いて上肢を分画し、上腕、前腕、手部の重量、ならびに肩甲帯部の除脂肪量を算出した。上肢、上腕、前腕、手部の重量、肩甲帯除脂肪量、肩甲帯除脂肪量に対する上腕重量の群間比較にはt検定もしくはMann-WhitneyのU検定を用いた。また、上腕重量、上肢重量、肩甲帯除脂肪量については群間の体格差を考慮するため、体重を共変量とする共分散分析を実施した。【結果】前腕重量、上腕重量、上肢重量はInjured Shoulder群がNon Injured群と比較して有意に高値を示した(p=0.045、0.014、0.028)。また、肩甲帯除脂肪量に対する上腕重量はInjured Shoulder群がNon Injured群よりも有意に高値を示した(p=0.045)。共分散分析の結果、肩甲帯除脂肪量はInjured Shoulder群がNon Injured群と比較して有意に低値(p=0.028)を示した一方、上肢および上腕重量は高値を示した(p=0.049、0.046)。【結論】投球障害の既往を有する中学野球選手は上肢重量に対して肩甲帯筋量が不足することが明らかとなった。肩痛の既往は肩障害再発の危険因子となることから、肩甲帯除脂肪量の発育がピークとなる中学生期に肩甲骨周囲筋のトレーニングを介入することは再発予防に貢献する可能性がある。(著者抄録)

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.

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.

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.

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.

PURPOSE: The flexor digitorum longus and posterior tibial tendon as well as the perforating veins are located along the distal posteromedial tibial border. Adipose tissue may surround these structures and possibly play a role in reducing mechanical stress. This study aimed to examine the adipose tissue along the posteromedial tibial border via magnetic resonance imaging (MRI), ultrasound, and gross anatomical examination. METHODS: The lower legs of 11 healthy individuals were examined every 3 cm from the medial malleolus using MRI and ultrasound. The fat fraction was calculated using fat fraction images. In addition, the gross anatomy of the flexor digitorum longus origin and adipose tissue along the posteromedial tibial border was examined in seven fresh cadavers. The fat fraction was compared at different heights along the posteromedial tibial border and in Kager's fat pads; we also compared the height of the flexor digitorum longus origin and adipose tissue. RESULTS: In vivo, the adipose tissue was identified along the entire posteromedial tibial border using MRI and ultrasound. There was no significant difference in fat fraction between Kager's fat pads and the adipose tissue along the posteromedial tibial border, except at the 6 cm mark. All seven cadavers presented adipose tissue along the posteromedial tibial border, significantly more distal than the flexor digitorum longus origin. CONCLUSION: The adipose tissue was identified along the posteromedial tibial border via MRI, ultrasound, and gross anatomical examination; thus, this tissue may play a role in reducing friction and compressive stress in tendons.

We aimed to investigate the changes caused by focused extracorporeal shock wave pain therapy (f-ESWT) in patients with patellar tendinopathy by means of ultrasound imaging. We included 18 knees from 11 college athletes with patellar tendinopathy. We assessed the tendon thickness and blood flow of the patellar tendon using ultrasound imaging, rest pain using NRS and tenderness using a pressure pain gauge. We recorded four measurements: immediately before f-ESWT (PRE 1) and after f-ESWT (POST 1) and two weeks after the first irradiation before f-ESWT (PRE 2) and after f-ESWT (POST 2). Only the resting pain in both the first and second irradiations showed a significant difference immediately before and after the treatment. In terms of pain changes after two weeks later, we observed significant differences in the resting pain between PRE 1 and PRE 2 and also in the resting pain, tenderness and blood flow area between PRE 1 and POST 2. No significant difference was seen in the tendon thickness. We concluded that pain in the patellar tendon at rest decreased before and after irradiation, suggesting that f-ESWT may have influenced the nociceptive structures and had an analgesic effect.

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.

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.

BACKGROUND: In understanding the onset factors associated with Plantar heel pain and the structure of heel fat pad, measuring its thickness is the most basic frequently reported evaluation. This study aimed to determine changes to heel fat pad thickness associated with age and gender and the relationship between heel fat pad thickness, age, and physique in Japanese. METHODS: This study was carried out in 1126 healthy individuals between the ages of 1 and 96 years. Participants were categorized according to age. Heel fat pad thickness was measured with an ultrasonography device using a linear ultrasonography probe. FINDINGS: Heel fat pad tends to become thicker from ages 1-5 to 30-44 years and thinner from ages 30-44 to 80-96 years. Heel fat pad thickness in males and females was similar within each group, and males had higher heel fat pad thickness than females of corresponding ages. Heel fat pad thickness of males had a good correlation with height and body mass. Moreover, male heel fat pad thickness had a fair correlation with age. Heel fat pad thickness of females had a moderate correlation with height and body mass and a fair correlation with age. INTERPRETATION: Heel fat pad thickness became thicker from ages 1-5 to 30-44 years and thinner from ages 30-44 to 80-96 years. Females had a lower heel fat pad thickness than males of corresponding ages. This result suggests that higher heel fat pad thickness in males is related to body mass and height.

It is important to understand the timing of the maximum increase of forearm-hand inertia value and lean body mass (LBM) of the shoulder girdle musculature when elbow injury frequently occurs. This study aimed to clarify the discrepancies of those in youth baseball players. Forty-three male baseball players (8- to 14-years-old) participated in this study. The forearm-hand inertia value and LBM of the shoulder girdle musculature were calculated using dual-energy X-ray absorptiometry (DXA). A cubic spline fit was applied to the annual increase forearm-hand inertia value and LBM of the shoulder girdle musculature for each chronological age and years from peak height velocity (PHV) age. As a result of cubic splines fitting, the peak timing for forearm-hand inertia value and LBM of the shoulder girdle musculature was 12.42 and 12.75 years in chronological age, -0.66 and -0.11 years in PHV age. Therefore, the peak timing of forearm-hand inertia value was about 4 months earlier in chronological age and half a year earlier in PHV age than LBM of the shoulder girdle musculature. Acquiring sufficient shoulder girdle musculature during the period when the growth of the shoulder girdle musculature cannot catch up with forearm-hand inertial value is necessary to reduce the elbow load while throwing.

The purpose of this study was to identify the growth changes of the inertial in baseball players from both chronological age and relative growth, and to play a part in the elbow injury prevention. The subjects were 184 baseball players from elementary school students to university students. A whole body scan was performed using a DXA device, and the forearm-and-hand inertia were calculated according to Ganley’s method of calculating the inertia. In addition, the inertia ratio was calculated by the forearm-and-hand inertia for the region of scapular lean mass and the inertia ratio of that under the condition of the ball holding. In addition, the allometry method was used to determine the inertia ratio and the inertia ratio of ball holding condition from the viewpoint of relative growth based on height. The inertial ratio showed the peak at the age of 12 or about 150 cm in height, suggesting an increased risk of elbow disorders at this time.

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.

踵骨下に存在する踵部脂肪褥は、heel fat padとも呼ばれる脂肪組織で、構成要素の異なる浅層のmicrochamber layer(MIC)と深層のmacrochamberlayer(MAC)の大きく2層から構成されており、歩行などの際にクッション機能として働く。本研究では、超音波B-modeによる押し込み手法の前後の変化量とMICとMACの硬度値の相関を検討し、クッション機能を評価する手法について検討することを目的とした。押し込み変化量とMICのSRとの相関は見られなかったが、MACのSRと有意な正の相関が見られた。RTE法による踵部脂肪褥の硬度測定は、MACの弾性評価に有用である。(著者抄録)