Effect of rebound jump improvements on reactive agility performance: Insights into joint mechanics during the takeoff phase

The relationship between rebound jump (RJ) performance and lower limb joint mechanics differs depending on task demands, such as pre-planned change of direction (COD) versus unanticipated agility. However, longitudinal associations with agility remain unclear. This study examined improvements in the RJ performance and their relationship with reactive agility performance, focusing on joint mechanics during takeoff. Twenty-five female soccer players completed sprint, RJ, COD, and reactive agility tests during the pre- and mid-seasons. Based on changes in reactive agility time, participants were classified into improved (n = 17) and non-improved (n = 8) groups. Performance variables and RJ takeoff mechanics were analyzed using 3D motion analysis and force plate. Linear mixed models and empirical best linear unbiased predictors were used to assess group effects and individual variability. Paired t-tests were used to evaluate within-group changes. The COD time and RJ-index (jump height/contact time) improved significantly, along with increased ankle negative power and knee eccentric torque. No changes were observed during sprint time and reactive agility time. However, the improved group showed improvements in reactive agility time, RJ performance, and joint mechanics, whereas the non-improved group showed only limited changes. Individual analysis revealed that those with a high baseline RJ-index improved further via increased hip joint output, whereas those with low initial values improved RJ-index, but not reactive agility performance. These findings support plyometric strategies that consider joint-specific eccentric requirements and initial performance characteristics.