Many elite female athletes struggle to maintain performance while transitioning from high school to university-level (senior) sports. This study explores factors of body composition that influenced performance in elite junior female track and field athletes transitioning to the senior division. Forty-two elite female track and field athletes, ranked among the top 100 in Japan, were enrolled in this study. Whole-body mode dual-energy X-ray absorptiometry scans were performed during the post-season of 2016 and 2017. Athletes’ performances were assessed using the International Association of Athletics Federation scoring system. Relationships between changes in performance and those in body composition were investigated. There were significant negative correlations between changes in performance and fat mass (FM), and percentage FM (FM%). This was seen in total body and lower extremities, and not in the trunk and upper extremities. In addition, there was a positive correlation between changes in performance and percentage lean mass (LM%). However, there were no correlations between changes in performance and LM and total mass. Elite female track and field athletes transitioning to senior division should decrease their FM and FM% and increase LM%, to sustain or improve performance. It is also more important to monitor changes in body composition than body mass.

Objective: To identify predictive risk factors of lumbar stress (LS) fracture developing from an asymptomatic stress reaction of the pedicle among adolescent male soccer players. Design: Prospective cohort study. Setting: Amateur Japanese adolescent male soccer team. Participants: Japanese adolescent male soccer players (n = 195) aged 12 to 13 years. Assessment of Risk Factors (Independent Variables): Height, body weight, body mass index, muscle tightness of both lower extremities (iliopsoas, hamstrings, and quadriceps), lumbar bone mineral content, developmental age, and lumbar lordosis angle were measured as baseline measurements. Main Outcome Measures (Dependent Variable): Players who were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle at baseline were followed; extension-based lumbar pain was defined 1 year after the baseline. The players were assigned to the LS fracture or control (CON) group at follow-up. Results: At baseline, 40 boys were diagnosed with an asymptomatic stress reaction of the lumbar spine pedicle. The difference in muscle tightness between the kicking leg and supporting leg was significantly different (P = 0.012) between the LS (n = 16) and CON (n = 22) groups. Increase in iliopsoas muscle tightness in the kicking leg was a predictive risk factor of developing extension-based lumbar pain after adjusting for developmental age and body mass index (odds ratio, 1.54; 95% confidence interval, 1.05-2.27). Conclusions: Development of extension-based lumbar pain from an asymptomatic stress reaction of the pedicle among adolescent male soccer players was associated with increased iliopsoas muscle tightness of the kicking leg relative to that of the supporting leg.

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.