The acute effects of assisted or resisted variable resistance back squat exercise on countermovement jump performance

INTRODUCTION: Back squat warm-up activities using elastic band (EB) resistance in combination with free weight resistance (FWR) can improve subsequent countermovement jump (CMJ) performance [1], a phenomenon termed post-activation performance enhancement (PAPE). However, across the literature sub-maximal loads of 85% are commonly used, with limited research existing on the effect of lighter loads on acute performance enhancement under both FWR or EB (resisted [RES] or assisted [ASS]) conditions. The aim of the present study was to compare the effects of back squats at 50% 1-RM under two EB attachment sites (ASS and RES) and FWR alone after a task-specific comprehensive warm-up on subsequent CMJ performance. METHODS: Twenty active males (age = 24.9±3.7 y, height = 1.7±5.7 m, mass = 83.4±12.6 kg) volunteered for the study and completed three separate experimental conditions (FWR, RES, ASS) separated by 48 h following a randomised crossover design. During each condition, participants first completed initial baseline CMJ tests (BL1) followed by a task-specific comprehensive warm-up that involved 5 min of cycling, two sets of 5 bodyweight squats, 5 continuous CMJs at 70% of perceived maximum, and finally, maximal CMJs every 30 s until 3 consecutive jumps were within 3% of jump height. Baseline 2 (BL2) CMJ tests were then completed and followed by 3 back squats following either the FWR, RES or ASS protocols at 50% 1-RM with 35% of the load generated by EBs during the RES and ASS conditions. CMJs were then performed 30 s, 4 min, 8 min and 12 min later. RESULTS: Significant increases (p<0.05) in both jump height (4.6-18.8%) and peak power (5.3-10.8%) were observed across all timepoints when compared with BL1 measure in all conditions. In the ASS condition, significant increases in jump height (4.6-11.8%) and peak power (6.5-2.0%) were observed at 30 s, 4 min, 8 min, and 12 min compared to BL2. In the RES condition, significant increases in jump height (7.1-1.2%) and peak power (2.3-5.4%) were observed at 30 s, 4 min, and 8 min, and in the FWR condition, significant increases in jump height (2.2-5.7%) and peak power (1-4.6%) were observed at 30 s and 4 min. DISCUSSION: The implementation of back squats into a warm-up activity at 50% 1-RM increased jump performance when EBs were used during both the ASS and RES conditions, with the increase in jump height being greater than that observed in the FWR condition. The use of EB resistance speculatively reduces loading at the sticking point, potentially allowing for greater acceleration during the concentric phase as lower-limb joints extend at the point where more optimal muscle lengths are achieved [2].These data have important implications for warm-up design for strength and power activities. REFERENCES 1. Mina et al. (2019). Scand J Med Sci Sports. 29(3):380-392. 2. Anderson et al. (2008). J Strength Cond Res. 22(2):567-574.