Purpose: Correcting movement syndromes requires utilizing compound movements which maximally activate prime mover muscles such as the gluteus maximus (GM). This study aimed to examine prime mover and synergist muscle activity at varied training loads during the back squat, a common lower body corrective and training exercise. Methods: Muscle activity was examined using surface electromyography in the GM, rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), vastus medialis (VM), and semitendinosus (ST) at six intensities (10% intervals) from 40 to 90% of one-repetition maximum (1RM) during the back squat. Repeated measures ANOVAs were utilized in statistical analysis. Results: Training load had a significant effect on the GM, RF, and VL (p < 0.05) during the descending phase and the VL, RF, GM, BF, and ST (p < 0.05) during the ascending phase of the back squat. The GM produced the greater muscle activity at 80% and 90% of 1RM than at 1RM during the ascending phase. The VM produced greater muscle activity at 80% of 1RM than at 1RM in both phases of the back squat. All other muscles were maximally activated at 1RM. Conclusions: These results suggest that when utilizing the back squat as a corrective exercise, the prime movers VM and GM are maximally activated at training loads of 80-90% of 1RM. After this point, synergist muscles are utilized to complete the movement, potentially lowering the muscle activity of the VM or GM.
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