How drop height- and fatigue-dominated overtraining affect performance and its underlying mechanisms

The aim of this study was to analyse the effects of fatigue and drop height on the biomechanical characteristics of drop jumping movements, with a focus on revealing the mechanisms through which these factors increase the risk of injury. Standard drop jump (DJ) tests were conducted at two different drop heights (0.4 m and 0.8 m) before and after functional fatigue. Motion performance and biomechanical indicators were statistically analysed, and an innovative spring–damper model was used to analyse the joint stiffness and damping coefficients. Increased drop height and fatigue significantly prolonged the ground contact time (by 26.5 % and 13.6 % at 0.4 m and 0.8 m, respectively) and reduced the jump height (by 29.0 % and 24.6 %, respectively). The reactive strength index and average power output decreased. Higher drop heights led to greater ground reaction forces and increased knee stiffness during the initial impact phases (S 1 and S 2 ). Fatigue further impaired neuromuscular function, reducing the joint range of motion and increasing joint stiffness and damping coefficients. This study highlights the importance of balancing external (drop height) and internal (fatigue) factors in DJ training to maximize performance and minimize injury risk. These findings provide a foundation for optimizing training protocols by considering individual biomechanical adaptations and emphasize the need for further research into the mechanisms underlying overtraining, particularly with a more diverse participant pool.