Variable Versus Constant Resistance Squat Training for Lower-Limb Strength and Power: A Systematic Review and Meta-Analysis

The superiority of Variable Resistance Training (VRT) over traditional Constant Resistance Training (CRT) for enhancing lower-limb performance is debated, with previous meta-analyses limited by aggregating disparate exercises. This systematic review and meta-analysis, the first to focus exclusively on the squat, compared the acute and long-term effects of VRT versus CRT on maximal strength and explosive power. Following PRISMA guidelines, 20 studies were analyzed (literature search up to 15 June 2025), with Hedges’ g used for effect size (ES) calculation. Results demonstrated VRT’s superiority for both acute (ES = 0.34) and long-term adaptations. Acutely, effects peaked with an 8–12 min recovery (ES = 0.43). Long-term, VRT produced greater gains in maximal strength (ES = 0.31) and explosive power (ES = 0.17). Subgroup analyses on maximal strength revealed that elastic bands were highly effective (ES = 0.67), particularly in trained individuals (ES = 0.35), males (ES = 0.41), within cycles < 8 weeks (ES = 0.44), and at frequencies of ≤2 sessions/week (ES = 0.45). For explosive power, chains were most effective (ES = 0.37), significantly improving jumping performance but not sprinting. In conclusion, VRT is a more effective modality for squat training; optimal programs should utilize elastic bands for strength and chains for power, with strength-focused blocks being short-term (<8 weeks) and lower-frequency (≤2 sessions/week) for trained individuals.