Inter-day reliability and usefulness of reactive strength index derived from two maximal rebound jump tests

Purpose: This investigation examined the inter-day reliability and usefulness of reactive strength index (RSI) derived from a maximal 5 rebound jump test (5max RJT) and a maximal 10 rebound jump test (10/5 RJT). Methods: Twenty male field sport athletes (24.5±3.0 y; 1.78±0.1 m; 84.9±5.2 kg) performed 2 maximal repetitions of the 5max RJT and the 10/5 RJT on two testing days following a specific warm up. A one week period separated each testing day and these sessions were proceeded by a familiarisation session. RSI was calculated by dividing jump height (m) by contact time (s). The 5max RJT and the 10/5 RJT trial with the highest RSI on each testing day was used for reliability and usefulness analysis. Results: Both tests were deemed reliable for determining RSI for male, female and pooled male and female cohorts as the ICCs ≥ 0.80 and the CV ≤ 10%. Only the 5max RJT was rated as ‘good’ at detecting the smallest worthwhile change (SWC) in performance for female athletes (SWC: 0.10 ˃ TE:0.07). The 5max RJT for males and the 10/5 RJT for males and females were rated as ‘good’ in detecting a moderate change in performance only. Conclusions: Both tests are reliable for the determination of RSI but the usefulness of the tests in detecting the SWC is questionable.