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

Area of Science:

• Sports Science
• Biomechanics
• Strength and Conditioning

Background:

• Free-weight resistance training (FWT) imposes constant resistance, potentially limiting velocity and power output due to a sticking region.
• Variable resistance training (VRT) offers a method to modify resistance throughout the range of motion.

Purpose of the Study:

• To compare the effects of FWT versus VRT (15%, 25%, 35%) on back squat kinetics and kinematics during the concentric phase.
• To determine if VRT can improve velocity and power output by mitigating the effects of the sticking region.

Main Methods:

• Twenty resistance-trained men performed back squats at 90% of their one-repetition maximum under four conditions: FWT and VRT at 15%, 25%, and 35%.
• Kinetic and kinematic data were collected using force plates and linear position transducers.
• Statistical analysis involved one-way repeated-measures ANOVA with Bonferroni post hoc tests.

Main Results:

• No significant differences were observed in peak velocity, peak power, peak force, or mean force between conditions.
• Increasing VRT percentages significantly reduced sticking region duration and force at zero velocity.
• Mean concentric velocity, velocity at sticking region onset, and mean concentric power increased with higher VRT percentages.

Conclusions:

• Variable resistance training (VRT) enhances back squat mean concentric velocity and power output.
• VRT is an effective alternative to FWT for improving specific performance characteristics by reducing force at zero velocity and increasing velocity at sticking region onset.