Test-Retest Reliability and Usefulness of a Foot-Ankle Rebound-Jump Test for Measuring Foot-Ankle Reactive Strength in Athletes.

This study investigated the test-retest reliability and usefulness of the foot-ankle rebound-jump test (FARJT) for measuring foot-ankle reactive strength metrics in athletes. Thirty-six highly trained, healthy athletes (5 female; 21.5 [3.9] y; 1.80 [0.10] m; 72.7 [10.4] kg) performed 8 repeated bilateral vertical foot-ankle rebound jumps on 2 testing days. Testing days were 1 week apart, and these sessions were preceded by a familiarization session. Reactive strength metrics were calculated by dividing jump height (in meters) by contact time (in seconds) for the reactive strength index (RSI) and flight time (in seconds) by contact time (in seconds) for the reactive strength ratio (RSR). The mean of 4 jumps (excluding the first and last 2 jumps) on each testing session were considered for RSI and RSR reliability and usefulness analysis. We found a high reliability of the FARJT for RSI (intraclass correlation coefficient [ICC] > .90 and coefficient of variation [CV] = 12%) and RSR (ICC ≥ .90 and CV = 8%). Regarding their usefulness, both RSI and RSR were rated as "marginal" in detecting the smallest worthwhile change (typical error > smallest worthwhile change) and "good" in detecting a moderate change in performance. The results showed that a FARJT is a highly reliable test for measuring foot-ankle reactive strength in athletes and useful for quantifying changes, for example, following a training block. However, its usefulness as an accurate daily or weekly monitoring tool in practice is questionable.