The Integral Reactive Strength Index: An Accurate Measurement for Evaluating Drop Jump Performance in Sprinter Athletes

Abstract

The reactive strength index (RSI) is a performance measure previously used to assess lower extremity performance; however, this study addresses limitations in its interpretation that need to be readdressed. The purpose of this study is twofold: to test the correlation of a new variable denominated integral reactive strength index (IRSI) with the RSI and to compare the flight time, ground contact time, jump height, RSI, reactive capacity, and IRSI between Olympic athletes in 100 m and 400 m. Ten elite male track and field athletes who qualified for the Olympics participated in this study (age = 24.9 ± 2.42 years; height = 1.75 ± 5.0 cm). They were divided into two groups, the first with five 100 m sprinters and the second group with five 400 m sprinters. The drop jump (DJ) attempts from 0.20 m were performed with the force plate 0.10 m away from the jump box. The DJ 0.30 m and DJ 0.40 m had a 0.15 m separation, and the DJ 0.50 m and DJ 0.60 m had a 0.20 m separation. The correlation analysis showed a high correlation (r = 0.805; p = 0.02) between the RSI and the IRSI. The comparisons between 400 m sprinters versus 100 m sprinters showed that there are no significant differences between the groups for any of the reactive strength variables (p > 0.05). Coaches of these sports’ specialties should take these criteria into account when developing plyometric programs and introduce the IRSI as an accurate measurement for evaluating DJ performance.