Acute Effects of Intracontrast Rest After Back Squats on Vertical Jump Performance During Complex Training

Houlton, LJ, Moody, JA, Bampouras, TM, and Esformes, JI. Acute effects of intracomplex rest after back squats on vertical jump performance during complex training. J Strength Cond Res 38(11): e645-e655, 2024-Postactivation performance enhancement and complex-contrast sets are prevalent in sports science research. Typical complex-contrast sets consist of heavy back squats, an intracontrast rest period (ICRP) and vertical jumps (countermovement jumps [CMJs], or squat jumps [SJs]). Propulsive impulse (Jprop) is considered the leading indicator of jump performance. However, studies evaluating jump performance during complex-contrast sets use jump height as the primary performance measure, limiting insight into ICRP's effect on jump performance. We assessed the effect of a 3 repetition maximum (3RM) back squat and 6 ICRPs on vertical jump Jprop and associated force-time components. Fourteen subjects completed 12 experimental conditions, assigned equally to 4 testing sessions. Independent variables, in a 6 x 2 randomized, counterbalanced design, were ICRP (0, 60, 120, 180, 240, 300 seconds; ICRP0, ICRP60, ICRP120, ICRP180, ICRP240, ICRP300, respectively) and vertical jump (CMJ and SJ). Conditions consisted of baseline vertical jumps, followed by 3 back squat repetitions at 100% 3RM, an ICRP and experimental jumps. Symmetrized percentage changes between experimental and baseline jumps were assessed using repeated measures analysis of variance (ANOVA) and pairwise effect sizes. Results showed significant effects (p <= 0.05) on CMJ average rate of force development (RFD) between ICRP0 and ICRP120 and ICRP0 and ICRP300. Pairwise comparisons showed medium and large effect sizes for and increases in CMJ RFD (g = 0.83-2.69) whereas SJ RFD decreased (g = 0.81-2.57). Small effect sizes were found for Jprop, peak force, and mean force. Results suggest limited change in Jprop (g = 0.01-0.58), but back squats may potentiate RFD via the stretch-shortening cycle.