Effects of plyometric exercise training with optimal drop heights on reactive strength, maximal strength, and vertical stiffness in junior basketball players: a randomised controlled trial

This study examined the effects of 8 weeks of low-to-moderate intensity plyometric training with optimal drop heights on maximal isometric strength, vertical stiffness, and reactive strength in junior male basketball players. Participants were randomly divided into training (<i>n</i> = 20) and control (<i>n</i> = 20) groups from 3 teams with same division in the state league. Before and after 8 weeks of training, the drop jump (DJ) and isometric mid-thigh pull (IMTP) tests were performed to evaluate force-time measures. The optimal drop height was determined as the height that provided the highest reactive strength index (RSI). The ground contact phase during the DJ was divided into 2 subphases, braking and propulsion, for a detailed analysis of force-time curves. The analyses revealed that plyometric training significantly improved RSI (<i>p</i> < 0.001, Cohen's <i>d</i> = 1.507), ground contact (<i>p</i> < 0.001, <i>d</i>=-1.255), braking (<i>p</i> = 0.001, <i>d</i>=-1.066) and propulsion phase (<i>p</i> < 0.001, <i>d</i>=-1.078) time. Significant improvements were observed in the peak vertical ground reaction force (<i>p</i> < 0.001, <i>d</i> = 1.715), peak centre of mass displacement (<i>p</i> = 0.005, <i>d</i>=-0.989), vertical stiffness (<i>p</i> = 0.004, <i>d</i> = 0.983). However, there was no significant difference in the jump height (<i>p</i> = 0.382, <i>d</i> = 0.267) and maximal isometric strength (<i>p</i> = 0.602, <i>d</i> = 0.147). Plyometric training provided improvements in reactive strength, vertical stiffness, but did not improve maximal isometric strength.