Using Reactive Strength Index-Modified as an Explosive Performance Measurement Tool in Division I Athletes

Abstract

The purposes of this study included examining the reliability of reactive strength index-modified (RSImod), the relationships between RSImod and force-time variables, and the differences in RSImod between male and female collegiate athletes. One hundred six Division I collegiate athletes performed unloaded and loaded countermovement jumps (CMJs). Intraclass correlation coefficients and typical error expressed as a coefficient of variation were used to establish the relative and absolute reliability of RSImod, respectively. Pearson zero-order product-moment correlation coefficients were used to examine the relationships between RSImod and rate of force development, peak force (PF), and peak power (PP) during unloaded and loaded jumping conditions. Finally, independent samples t-tests were used to examine the sex differences in RSImod between male and female athletes. Intraclass correlation coefficient values for RSImod ranged from 0.96 to 0.98, and typical error values ranged from 7.5 to 9.3% during all jumping conditions. Statistically significant correlations existed between RSImod and all force-time variables examined for male and female athletes during both jumping conditions (p ≤ 0.05). Statistically significant differences in RSImod existed between male and female athletes during both unloaded and loaded CMJs (p < 0.001). Reactive strength index-modified seems to be a reliable performance measurement in male and female athletes. Reactive strength index-modified may be described and used as a measure of explosiveness. Stronger relationships between RSImod, PF, and PP existed in female athletes as compared with that in male athletes; however, further evidence investigating these relationships is needed before conclusive statements can be made. Male athletes produced greater RSImod values as compared with that produced by female athletes.

Modified Reactive Strength Index in Adolescent Athletes Competing in Different Sports and Its Relationship with Force Production

“…Previously established moderate to large correlations of RSImod with the rate of force development (RFD) indicate that RSImod can be used to measure explosiveness in athletes [5,6]. In a recent study [7] the authors confirmed the validity of the RSImod as a measure of explosiveness, suggesting that RSImod incorporates both essential factors of explosiveness, namely force and speed.…”

“…t ecc was defined as the time duration from the start to the deepest point of the countermovement (velocity is zero); t con was the time duration from the bottom of the countermovement to the moment of takeoff. Total time of the jump (t total ), as described elsewhere [5] is the time duration from the start of the countermovement to takeoff and was calculated by adding t ecc and t con . The ratio of t ecc to t total was calculated and expressed as percentage.…”

“…Total vertical displacement (Vh total ) was calculated by adding vertical displacement during the eccentric and the concentric phases of the jump. Jump height was calculated based on the flight time method [2,5,14]. Flight time was calculated from the moment of takeoff to the moment of landing.…”

“…Reliability studies with RSI [3,4] or with RSImod [2,5] have shown high reliability for both measures. Previously established moderate to large correlations of RSImod with the rate of force development (RFD) indicate that RSImod can be used to measure explosiveness in athletes [5,6].…”

“…Studies with RSImod so far have included adult athletes [2,5,7] revealing differences between male and female athletes [5] or between different plyometric exercises [2]. Between the ages of 15 to 18, young athletes at high competition levels quite often are exposed to considerable training loads designed to prepare them to compete at the adult level.…”