Does task experience moderate habituation effects in drop jumps? - An intra- and interday reliability and measurement error analysis

Drop jumps (DJs) are common tests for determining stretch-shortening cycle efficiency. Despite their wide implementation, numerous studies did not adhere to validity guidelines, and participants reached ground contact times (GCTs) of > 250ms. The DJ is a coordinatively-demanding task and it could be hypothesized that a lack of adherence to GCT thresholds could be attributed to insufficient test familiarization. Accordingly, this study evaluated the impact of extensive task habituation on test-retest reliability and GCT adherence. Eighty-nine healthy participants were allocated to an experienced and inexperienced subgroup. All subjects performed DJs on five days from three different drop heights, with three trials per height (5 × 3 × 3 DJs = 45 jumps). Reliability coefficients and test-retest systematic and random errors were quantified between testing days. The inexperienced subgroup showed systematic performance increases between test day 1 and the subsequent days in most evaluated parameters with largest effects obtained for GCTs (up to d = 0.83, p  < 0.001). With up to 30%, the MAPEs peaked for reactive strength index (RSI) in the day 1 to day 5 comparison. No systematic test-retest increases occurred in the experienced group, and the random percentage error was meaningfully smaller (16–17% for the RSI). The systematic bias observed in the inexperienced subgroup might indicate significant task habituation, while the experienced group was already familiar with the testing procedure and showed no test-retest improvements. Since subgroup measurement errors differed meaningfully (e.g. 16% versus 30% RSI MAPE), future DJ research should provide their own reliability quantifications and sufficient habituation.