No Changes in Depth Jump Height but Longer Ground Contact Times as Box Height Increases

Abstract

Depth jumps (DJ) are commonly implemented in plyometric training programs in an attempt to enhance lower extremity jump performance. However, it is unknown how different box heights affect jump height (JH) and ground contact time (GCT). PURPOSE: To assess JH and GCT of depth jumps from various box heights. METHODS: College students who engaged in plyometric training (M=13, F=7; age: 22.8±2.7y, height: 175.65±11.81cm, mass: 78.32±13.50kg) performed DJs from 30cm (DJ30), 45cm (DJ45), 60cm (DJ60), 76cm (DJ76), and 91cm (DJ91). A 16 camera Vicon system was used to tract reflective markers bilaterally to calculate JH (ASIS, PSIS), while a Kistler force plate was used to measure GCT. JH and GCT were compared using separate 2x5 (sex x box height) repeated measures ANOVAs. RESULTS: There was no interaction but there was a significant main effect for sex where both JH (M>F) and GCT (F>M) showed a significant M bias. There was no box height main effect for JH (DJ30 .4934±.1126m, DJ45 .5003±.1134m, DJ60 .4936±.1195m, DJ76 .4957±.1105m, DJ91 .4783±.1162m) but there was for GCT where DJ30 (.358±.097s), DJ45 (.360±.105s) and DJ 60 (.372±.104) were not significantly different from each other but were all less than DJ76 (.396±.116) and DJ91 (.420±115). CONCLUSION: Increasing box height beyond 60cm increased GCT but did not affect JH. Therefore, practitioners designing plyometric training programs to increase JH that implement DJs may utilize box heights between 30 and 60cm. This would insure minimal GCT which might be vital in other power and speed events.