Partial Bodyweight-Supported Squats Elicit Eccentric Contraction of the Thigh Muscles

Abstract

Purpose The study aimed to investigate how different levels of supporting forces during the squat exercise at a self-selected speed, along with different knee angles, affect fascicle length, pennation angle, and muscle activation for healthy young individuals. Methods Twelve healthy subjects participated in the study to measure fascicle length and pennation angle of the vastus lateralis (VL) at 0°, 60°, and 80° knee flexion. Leg muscle activities and the ground reaction force (GRF) were measured during squats using a squat aid machine with three supporting force levels. Results VL fascicle length and pennation angle at 0° knee flexion were significantly lower than at 60° and 80° flexion across all force levels (p < 0.05). Moreover, the leg muscles’ mean maximum electromyography and the three-direction normalized GRFs measured on both the squat aid machine and the subjects’ feet showed no significant variations across supporting forces. Conclusion Our findings indicate that squat exercise has the potential to induce eccentric contraction by increasing fascicle length and muscle activation and decreasing pennation angle, regardless of the supporting force level. Therefore, a squat aid machine for squats is recommended as a safe and effective approach to enhance muscle force through eccentric contractions.