Dual-task interference in the drop jump: Frequentist, Bayesian, and waveform analysis of vertical ground reaction force

To ensure standardization, reliability, and maximal performance, physical performance tests are usually performed with little to no cognitive load. However, during training and competition, athletes usually perform physical actions while under the demands of a concurrent cognitive task (CT). This study examined the effect of a concurrent CT on the force-time metrics of the drop jump (DJ) and their reliability under single-task (DJ without a CT) and dual-task conditions (DJ with a CT based on simple arithmetic calculations). Thirty-five healthy young participants performed single-task and dual-task DJ trials in a randomized order. Nineteen force-time metrics covering the braking, propulsion, and landing phases of the DJ were compared between conditions using paired t-tests with Holm adjustment and Hedges’ g z , Bayesian paired t-tests, and statistical parametric mapping (SPM) of vertical ground reaction force (VGRF) waveforms. For three-trial mean scores, 17 of the 19 metrics had within-session intraclass correlation coefficients (ICCs) of 0.812–0.930 across both conditions. Under the dual-task condition, jump height (p < 0.001, g z =1.40, Bayes factor BF 10 = 1.76 × 10 7 ) and reactive strength index (p < 0.001, g z =1.04, BF 10 = 45,943) were lower, while ground contact time was longer (p = 0.025, g z =−0.57, BF 10 = 20.57). SPM showed that VGRF was significantly lower under the dual-task condition during 29.2–34.3% (within braking) and 52.0–79.1% (within propulsion) of ground contact. In the landing phase, VGRF was significantly lower under the dual-task condition during 1.3–6.3% (initial force rise) and significantly higher during 15.5–19.6% (attenuation of the impact force). The spring-like correlation (p = 0.462, g z =0.20, BF 01 = 2.79) and the vertical time to stabilization (p = 0.462, g z =0.15, BF 01 = 3.74) showed no significant difference between conditions, with weak and moderate evidence for the absence of an effect. These findings suggest that a concurrent CT reduces force production within both the braking and propulsion phases of the DJ and alters the VGRF waveform during the subsequent landing phase in healthy young participants.