Investigation of Optimal Depth Jump Box Height for Reactive Strength Index

Reactive strength index (RSI) is used to assess athleticism through use of the stretch-shortening cycle for power and is determined by jump height over ground contact time. RSI is typically assessed utilizing an incremental drop jump test and while it is well-established that plyometric training positively impacts power production, the optimal depth jump box height for RSI remains unknown. PURPOSE: To measure RSI between different depth jump starting heights. METHODS: 20 college students were recruited for this study (M=13, F=7; age: 22.8±2.7y, height: 175.65±11.81cm, mass: 78.32±13.50kg) and were prepped using reflective markers on their ASIS and PSIS, bilaterally, which allowed for vertical jump height measurements. After a specific warm-up, subjects were instructed to perform three maximal DJs onto a force plate from five different heights: 30cm (DJ30), 45cm (DJ45), 60cm (DJ60), 76cm (DJ76), and 91cm (DJ91). RESULTS: A repeated measures ANOVA revealed no effect of sex but significant differences in RSI between starting heights (DJ30=1.36±0.11; DJ45=1.42±0.12; DJ60=1.35±0.12; DJ76=1.28±0.12; DJ91=1.16±0.11), with DJ45 and DJ60 being greater than DJ30, DJ76, and DJ91. CONCLUSION: A parabolic relationship was observed between depth jump box height and RSI, with the optimal depth jump starting heights being 45 and 60 cm. A potential avenue for future research would be to investigate training effects on RSI from various depth jump box starting heights.