Differential effects of jump-induced fatigue on lower-extremity landing biomechanics in children and adults.

PURPOSE: The purpose of this study was to investigate whether jump-induced fatigue differentially affects lower-extremity landing biomechanics in children and adults. METHODS: Twelve children and twelve adults completed alternating sets of twenty countermovement jumps and twenty drop jumps from a 30-cm box for at least three cycles, with 5 sec of rest between cycles. Before and after fatigue, all participants performed three countermovement jumps, and lower-extremity joint angles, joint moments, and vertical ground reaction force during the landing phase were collected. Time series data and discrete variables were analyzed using mixed design analyses of variance to examine the main effects of group and fatigue, as well as their interaction. RESULTS: CMJ performance decreased after fatigue, as reflected by lower CMJ height, shorter flight time, and reduced take-off velocity. Interaction effects between fatigue and group were observed for the ankle sagittal plane angle, hip frontal plane angle, ankle sagittal plane moment, and subtalar frontal plane angle. After fatigue, children showed a more plantarflexed ankle posture, greater hip adduction, and lower ankle plantarflexion and subtalar inversion moments. Fatigue also reduced hip and knee flexion angles overall, whereas adults showed greater peak hip flexion, peak knee flexion, and ankle moment output after fatigue. CONCLUSIONS: Age-related differences were observed in landing responses to fatigue. Children displayed a more constrained landing adjustment under fatigued conditions, whereas adults retained greater hip and knee flexion and higher ankle plantarflexion moment output, suggesting a more flexion-preserving strategy.