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Background Diminished balance is associated with the incidence of ankle and lower extremity injuries in adolescents. Although flexible flatfoot is a common foot condition in pediatric and adolescent populations, the association between balance control and foot morphology remain unclear in adolescent athletes. Methods Rearfoot angle in the double-limb standing position, body mass index (BMI), and isometric muscle strength related to the knee joint were retrospectively reviewed in 101 adolescent athletes (75 boys and 26 girls) with a mean age of 14.0 years (range 12–17). Postural stability during single-leg standing on static and dynamic platforms was investigated using Balance System SD in 119 feet without functional ankle instability. The participants were divided according to their rearfoot angle into control (less than 7°) and valgus (greater than or equal to 7°) groups. The measured parameters were compared between the control and valgus groups using Welch’s t-test, and P values Results The average rearfoot angle was 4.6° in all participants. An excessive valgus rearfoot angle was detected in 53 feet (26.2%). No significant difference was found between the groups in terms of BMI and isometric knee muscle strength. Although no statistical differences were observed in postural stability on the static platform between the control and valgus groups, the valgus group demonstrated poorer postural stability for single-leg standing on the dynamic platform. Multiple regression analysis revealed that BMI and rearfoot angle were significantly associated with a poor postural control on the dynamic platform. Conclusions Our findings suggest that excessive rearfoot valgus specifically contributes to the deterioration of postural stability in adolescent athletes, and that rearfoot alignment should be evaluated for the adolescent population to prevent sports-related lower extremity injury.

Objective. The physical condition of athletes can be assessed easily and quantitatively using objective indicators. Bioelectrical impedance measures the phase angle (PA), representing hydration and cell function, and is a potential clinical indicator of physical condition. This study aimed to investigate the association between PA and physical performance in adolescent athletes. Approach. Overall, 170 adolescent athletes underwent a sports medical check-up, including body composition measurements and physical performance tests. Whole-body and segmental PAs (arm and leg) were determined based on body composition values. Isometric grip power and knee isokinetic muscle strength were measured as parameters of muscle strength. Counter movement jump height and squat jump height were measured as jump parameters. Associations between PA and each muscle strength or jump parameters were analysed using Pearson product-moment correlation coefficient or Spearman’s rank correlation coefficient. Main results. Whole-body and upper limb PAs were highly correlated with grip power (r = 0.70–0.80). Whole-body and lower limb PAs were correlated with knee isokinetic muscle strength (r = 0.43–0.59). Whole and all segmental PAs were correlated with counter movement jump height (r = 0.46–0.57) and squat jump height (r = 0.42–0.52). Significance. PA can be used to monitor physical condition and sports performance in adolescent athletes. Segmental PAs can help assess the condition of the corresponding body part.

Design:Randomized controlled study.Setting:Laboratory.Participants:26 healthy swimmers randomly assigned to an exercise (n = 13; Ex) or control group (n = 13; Cont).Intervention:The Ex group performed respiratory-muscle exercises for 10 min thrice a week for 4 wk.Context:Respiratory-muscle exercises are used not only in the rehabilitation of patients with respiratory disease but also in endurance training for athletes. Respiration involves the back and abdominal muscles. These muscles are 1 of the elements responsible for posture control, which is integral to injury prevention and physical performance. However, the effects of respiratory-muscle exercise on posture remain unclear.Objective:To examine the potential of respiratory-muscle exercise for improving posture.Main Outcome Measures:Spinal curvature, pulmonary function, and trunk-muscle strength were measured for both the groups at baseline and after 4 wk. The data were compared between the Ex and Cont groups with Mann–Whitney U test and preintervention and postintervention within groups with a Wilcoxon signed rank-sum test.Results and Conclusion:The spinal curvature was significantly different in the Ex group, indicating a decrease in the thoracic (−13.1%, P < .01) and lumbar (−17.7%, P < .05) angles. The Ex group presented with lower thoracic (−8.6%) and lumbar (−20.9%) angles at postexercise than the Cont group (P < .05). With respect to trunk-muscle strength, only trunk-flexion strength significantly increased from pretest to posttest in the Ex group (P < .05). For pulmonary function, forced vital capacity and forced expiratory volume in 1.0 s were significantly increased after 4 wk in the Ex group (P < .05). The results suggest that respiratory-muscle exercise straightened the spine, leading to good posture control, possibly because of contraction of abdominal muscles.