Variable Resistance Training Improves Velocity and Power Output by Reducing Concentric Deceleration in the Back Squat

Chiang, YC, Lin, WC, Weakley, J, and Chiang, CY. Variable resistance training improves velocity and power output by reducing concentric deceleration in the back squat. J Strength Cond Res 40(7): e663-e669, 2026-Free-weight resistance training (FWT) presents constant resistance, potentially causing a sticking region that negatively affects velocity and power outputs. We aimed to compare FWT with 15, 25, and 35% variable resistance training (VRT) using elastic bands on back squat kinetics and kinematics in the concentric phase. Twenty resistance-trained men performed back squats at 90% of their one-repetition maximum across the 4 conditions in a counterbalanced order in a single session. Resistance in VRT conditions was normalized to ensure the average resistance was equivalent to the FWT condition. Kinetic and kinematic data in the concentric phase were recorded using force plates and linear position transducers. One-way repeated-measures analysis of variance with Bonferroni post hoc comparisons compared dependent variables between conditions. Significance was set at p ≤ 0.05. No significant differences were found between conditions for peak velocity, peak power, peak force, or mean force in the concentric phase. However, a dose-response relationship was observed for other variables. Increasing the VRT percentage led to a significant reduction in sticking region duration, particularly at 25% and 35%VRT, and a significant decrease in force at zero velocity. Conversely, mean concentric velocity, velocity at sticking region onset, and mean concentric power all increased with higher VRT percentages. In conclusion, VRT enhances back squat concentric mean velocity and power output by reducing force at zero velocity and increasing velocity at sticking region onset, representing an effective alternative to FWT for improving these specific performance characteristics.