Differential Effects of Standing Widths and Foot Abduction Angles on Muscle Synergy During Squatting in Adult Males

The effects of foot abduction angle and stance width on muscle activation remain inconsistent in current research. We aim to investigate this issue from the perspective of muscle synergies, thereby providing evidence-based squatting guidelines for sports training and rehabilitation. Nineteen males performed squats under six conditions: three widths (wide, medium, narrow) × two foot abduction angles (0°, 30°). Surface electromyography was recorded from seven lower limb muscles. We employed principal component (PC) analysis to investigate the muscle synergies of seven lower-limb muscles. Repeated-measures two-way ANOVA was performed to statistically analyze both muscle peak activation and PC scores, with significance set at p <. 05. Results In the descending PC3, which is primarily composed of the peroneus longus and vastus lateralis, 0° abduction scores were higher than 30° ( p =.003); narrow stance scores were higher than wide stance ( p =.017). In the ascending PC2 is composed of vastus lateralis, rectus femoris, and soleus, the score at 0° abduction was higher than that at 30° abduction ( p =.046). The other PCs were statistically non-significant ( p >.05). Increasing foot abduction angle and stance width appear to shift neuromuscular control from a strategy dominated by stabilizer muscles toward one dominated by the prime movers, indicating that in healthy adult men, simple adjustments to these stance parameters can predictably redistribute muscular load between stabilizer muscles and prime movers. • Effects of foot abduction angle and stance width on muscle synergies during squats were investigated. • Abduction angle and stance width affected peroneus longus and vastus lateralis activation during descending. • Vastus lateralis, rectus femoris, and soleus were affected by the abduction angle during ascending. • Wider stance width and greater foot abduction angle during squats could optimize muscular development.