Volleyball Competition on Consecutive Days Modifies Jump Kinetics but Not Height

Purpose: In volleyball, jump execution is critical for the match outcome. Game-play-related neuromuscular impairments may manifest as decreased jump height (JH) or increased jump total duration, both of which are pivotal for performance. To investigate changes in JH and kinetics with game play, the authors conducted a prospective exploratory analysis using minimal-effect testing (MET) and equivalence testing with the 2 one-sided tests procedure, univariate, and bivariate functional principal component analysis, respectively. Methods: Twelve male varsity athletes completed 3-set matches on 2 consecutive days. Countermovement jumps were performed on a force platform immediately prematch and postmatch on days 1 and 2 and once on days 3 and 4. Results: Across sessions, JH was equivalent (P < .022, equivalence test), while total duration reported inconclusive changes (P > .227). After match 2, MET indicated that relative force at zero velocity (P = .036) decreased, while braking duration (P = .040) and time to peak force (P = .048) increased compared with baseline. With the first and second functional principal components, these alterations, together with decreased relative braking rate of force development (P = .092), were already evident after match 1. On day 4, MET indicated that relative peak force (P = .049), relative force at zero velocity (P = .023), and relative braking rate of force development (P = .021) decreased, whereas braking duration (P = .025) increased from baseline. Conclusions: Impairments in jump kinetics were evident from variables related to the countermovement-jump braking phase, while JH was equivalent. In addition to these experimental findings, the present research provides information for the choice of sample size and smallest effect size of interest when using MET and 1- and 2-dimensional analyses for countermovement-jump height and kinetics.