Reduced metabolic energy cost in bounce squats driven by lower vasti contribution during the eccentric phase

The back squat is a fundamental resistance exercise, yet technical variations such as bounce squats may substantially alter energetic demands. While previous research highlighted mechanical and neuromuscular effects of the stretch-shortening cycle, the phase-specific and muscle-specific metabolic consequences of bounce squats remain unclear. To inform training strategies aimed at improving movement economy or managing fatigue during high-volume training, this study examined how bounce influences whole-body and muscle-level metabolic energy cost across different loads using musculoskeletal simulation.

Nine resistance-trained adults performed bounce and standard squats under five loading conditions (0-100% body weight) while motion capture, ground reaction forces, and surface EMG were recorded. Musculoskeletal modeling was used to estimate instantaneous metabolic power, integrated to compute phase-specific energy costs.

Two-way repeated-measures ANOVA revealed that bounce squats reduced total metabolic energy cost by approximately 10.5% compared with standard squats (p < 0.001), with the most pronounced effect during the eccentric phase (25.5% lower, p < 0.001). Muscle-level analyses indicated that the vasti (VAS) consistently exhibited lower metabolic cost in bounce squats across loads during descent, highlighting their central role in energetic savings. In contrast, during the concentric phase, VAS and gluteus maximus costs scaled with external load, with no detectable benefit of bounce. Other lower body muscles showed statistical effects of squat type, but their absolute contributions were minimal.

These findings demonstrate that the energetic benefit of bounce squats is phase- and muscle-specific, reflecting the reduced metabolic cost of eccentric VAS control and tendon recoil during rapid reversal. Bounce squats may therefore enhance movement economy without diminishing mechanical loading, offering practical value for athletic performance and rehabilitation.