Electromyographic activity in four superficial muscles of the thigh and hip during performance of the back squat to three different depths with relative loading.

Introduction: Inconclusive previous research on squat depth and the evoked electromyography (EMG) activity muddles our understanding of muscle recruitment in the back squat. This study determined EMG activity as a function of squat depth in four superficial muscles of the lower limb using relative loading. Method: Eight resistance trained males (mean ± SD age: 21 ± 1 years) performed back squats to partial, parallel and full depth using depth-relative 5-repetition–maximum loads. Muscle activity in the vastus medialis oblique (VMO), vastus lateralis (VL), gluteus maximus (GM), and biceps femoris (BF) during the concentric and eccentric phases of the squat was determined using surface electromyography. Peak (Peak EMG), mean (Mean EMG), and integrated (iEMG) EMG normalised to their respective maximum voluntary isometric contraction (MVIC) for each muscle were evaluated. Results: Three-way Anovas and Sidak post-hoc analysis revealed significant effects for squat type (p = 0.021 - 0.001), squat phase (p = 0.001), and muscle (p = 0.001). The significant differences were between the partial and the parallel squat (p = 0.016 - 0.001); for iEMG significant effects were also found between the partial and full squat (p = 0.001). The VMO elicited the highest EMG activity (e.g., Peak EMG 93.4 ± 36.9% MVIC; parallel squat, concentric) and the BF the lowest (e.g., Peak EMG 49.9 ± 14.7%). Greater GM activity occurred in parallel squats compared to full squats (mean difference in Peak EMG = 9.1% MVIC). Conclusion: The findings suggest that squatting to the parallel position or lower educes optimal contractile stimulation of the quadriceps. Squatting to parallel depth maximises EMG activation of the GM, possibly due to a more advantageous external moment arm or a reduction in neural drive.