Acute effects of rapid versus sustained isometric contraction durations on countermovement jump performance in national level young male soccer players

This study investigated the effects of different distributions of isometric conditioning activity (ICA) within a single set-1 s contraction performed 9 repetitions (RAPID) versus 3 s contractions performed 3 repetitions (SUST)-on countermovement jump (CMJ) performance in national level young male soccer players. Fifteen players completed three conditions: RAPID, SUST each involving maximal isometric contractions in the half-back squat position, as well as a control condition without ICA. Approximately 3 min pre-ICA and at 3-, 6-, 9- and 12-min post-ICA, the CMJ performance was assessed. The results showed a significant decrease in CMJ height and relative peak power following the RAPID protocol, with the greatest impairments occurring at 12 min post-ICA. In contrast, no significant changes were observed in the reactive strength index modified, contraction time, and countermovement depth. These results demonstrate that short, repetitive isometric protocols do not facilitate subsequent jump performance, with the RAPID protocol causing a transient decrease in CMJ performance. Therefore, the RAPID protocol should not be recommended as an acute strategy for enhancing jump performance in national level young soccer players.