The effects of added mass on the biomechanics and performance of countermovement jumps.

This study examined the kinetic and temporal differences between countermovement jumps (CMJs) and eccentrically loaded CMJs. A survey of 109 coaches and athlete showed that 87% of respondents regularly used jumps with added mass within training. Sixteen male and thirteen female track and field athletes from sprinting, hurdling and jumping events performed 5 bodyweight CMJs 5 jumps wearing a weighted jacket and 5 eccentrically loaded dumbbell (LDB) jumps trials in a randomised order. Peak force (PF), peak power (PP), flight time (FT), concentric time (CON-T), eccentric time (ECT), total time (TIME) and eccentric/concentric ratio (E/C-Ratio) were obtained from force plate data. Statistically significant differences (p < 0.05) with moderate to large magnitude effect sizes were found between men and women in FT, PP and PF but not in any of the temporal variables. The results indicated that the WJ decreased FT in men (↓9%) and women (↓10%) but LDB jumps had similar FT to CMJ. Overall, the results showed that LDB increased the E/C Ratio (↑50% and ↑42%) and decreased CON-T (↓37% and ↓25%) compared with WJ and CMJ respectively. LDB jumping is not recommended as a training modality as it tends to disrupt the relative timing of the jump action.