The aim of this study was to compare the effects of 3 sets of isometric conditioning activity (ICA), each with an equal total duration (9 s per set) but with different distributions contractions, on force production during ICA and subsequent countermovement jump (CMJ) performance. Fifteen resistance-trained males participated in this study (age: 22.1 ± 2.4 years; body mass: 85.1 ± 9.7 kg; height: 181.3 ± 6.5 cm; relative one-repetition maximum (1RM) in back squat: 1.59 ± 0.32 kg/kg of body mass). Participants completed 3 conditions, each consisting of ICA in the half-back squat with a pushing isometric muscle action (PIMA) position at a 120-degree knee angle against an immovable barbell, differing in repetition distribution: 3 sets of 9 repetitions lasting 1 s each (SUST-1), 3 sets of 3 repetitions lasting 3 s each (SUST-3), 3 sets of single repetitions lasting 9 s (SUST-9), and a control condition (CTRL) without ICA. A 1-minute rest was allowed between sets. Approximately 3 min pre-ICA and at 15 s, 3-, 6-, 9-, and 12-minutes post-ICA, the CMJ performance was assessed. Moreover, peak force (PF) production, and force generated at 100 (Force100) and 200 ms (Force200) during each ICA were evaluated. A two-way repeated measures ANOVA indicated a main effect of time on CMJ height (F = 2.674; p = 0.029; ηp2=0.171) but did not show significant differences between conditions (F = 0.934; p = 0.434; ηp2=0.067) or interactions (F = 0.826; p = 0.648; ηp2=0.060). Post-hoc comparisons indicated a significant decrease in CMJ height at the 9th minute compared to the 3rd minute (35.7 ± 5.6 cm vs. 36.8 ± 5.5 cm post-CA; d = 0.161; p = 0.048). In addition, no significant interactions or main effects were found for CMJ contraction time, PF and Force100 during ICA. However, a main effect of condition was demonstrated on Force200 (F = 19.181; p < 0.001; ηp2= 0.013). Post-hoc comparisons revealed higher Force200 values in SUST-1 (mean difference [MD] = 549 ± 137 N; d = 1.049; p < 0.001) and SUST-3 (MD = 348 ± 112 N; d = 0.665; p = 0.002) compared to the SUST-9 condition. None of the ICAs used in the present study had any effect on the CMJ performance. However, the significantly higher Force200 values noted in the SUST-1, and SUST-3 conditions compared to the SUST-9 condition suggest that the specific distributions of isometric contraction influence the force generated during their execution.

Department of Sports Games Faculty of Physical Education and Sport Charles University Prague Czech Republic

Institute of Sport Sciences The Jerzy Kukuczka Academy of Physical Education Katowice Poland

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