From eccentric force to explosive output: A multidimensional analysis of mechanical efficiency, neuromuscular strategy, and performance prediction in national-level junior badminton athletes undergoing overload training

This study aimed to investigate the neuromechanical pathways linking eccentric force production to explosive concentric output during countermovement jumps (CMJ) in national-level junior badminton athletes undergoing a specialized eccentric training program. Objective: 36 male athletes (age 16.5 ± 1.2 years) were quasi-randomly assigned to an experimental group (EG; n=18), which completed a 6-week supervised eccentric overload training in-volving flywheel squats and depth jumps thrice weekly, or a control group (CG; n=18), which maintained their habitual in-season training without additional interventions. Methods: Pre- and post-intervention assessments included CMJ performance measured on a force platform, with detailed analysis of kinetic and temporal variables such as eccentric peak force, rate of force development (RFD), reactive strength index (RSI), and novel indices of stretch-shortening cycle efficiency (SSC-Efficiency) and energy transfer ratio (ETR). Results: Path analysis revealed a significant direct effect of eccentric peak force on concentric peak power and jump height, independent of time to peak force, suggesting that enhanced eccentric force capacity translates directly into improved explosive output. Cluster analysis identified three distinct neuromuscular profiles among athletes, differing in mechanical efficiency and jump strategy, highlighting individual variability in response to eccentric training. Regression models using LASSO selection demonstrated that RSI, eccentric peak force, concentric impulse, and time to peak force collectively predicted jump height with high accuracy (R²=0.73). Notably, SSC-Efficiency and ETR pro-vided additional insights into the mechanical economy of force transfer during CMJ. Repeated measures ANOVA indicated significant improvements in RSI and ETR in the EG post-training, whereas CG showed no significant changes, confirming the efficacy of the eccentric overload intervention. However, classification models based on principal component analysis and linear discriminant analysis yielded moderate accuracy in distinguishing high- versus low-performance athletes, suggesting the need for further refinement. Conclusion: These findings underscore the critical role of eccentric force development in enhancing explosive performance in junior badminton players and support the integration of eccentric overload training in athlete development programs. The novel mechanical efficiency indices introduced may serve as valuable tools for individualized monitoring and optimization of neuromuscular function.