Influence of stance width and foot rotation on muscle activity and ground reaction forces during squats in female lacrosse players

Female lacrosse players experience a high burden of non-contact lower-extremity injuries, and squat-based neuromuscular training is commonly used to develop lower-limb strength, coordination, and load tolerance. How common technique modifications such as stance width and foot rotation affect joint excursion, muscle activation, ground reaction forces (GRFs), and inter-limb loading symmetry during squats in this population remains unclear. This study aimed to examine the effects of stance width and foot rotation on lower-limb joint excursion, surface electromyography (sEMG), GRFs, and inter-limb GRF asymmetry during bodyweight squats in female lacrosse players. Ten Japanese university-level female lacrosse players performed squats under six stance conditions (narrow, shoulder-width, wide × parallel or external rotation). sEMG was recorded from ten lower-limb muscles, synchronized with 3D kinematics and bilateral force plates. Friedman tests with false discovery rate (FDR) correction evaluated stance-related differences, with effect sizes estimated using Kendall’s W. Stance significantly influenced hip (χ² = 33.31, p < 0.001, W = 0.67), knee (χ² = 19.94, p = 0.001, W = 0.40), and ankle (χ² = 24.23, p < 0.001, W = 0.49) joint excursion. Wide external rotation (WidER) yielded the greatest hip joint flexion–extension excursion (116.9° ± 7.9°), whereas narrow parallel stance (NarPar) produced the smallest (98.2° ± 4.8°). During the descending phase, gluteus maximus activation was significantly higher in wide stances compared with narrow and shoulder-width conditions (q < 0.013). GRFs showed consistent vertical peaks across stances (∼56–62 % body weight), but mediolateral peaks were substantially higher in WidER (∼17 % body weight) than in narrow stances (∼5–7 % body weight). In female lacrosse players, squat stance meaningfully modulates mechanics even under bodyweight loading. WidER squats preferentially increase hip excursion, gluteus maximus activation, and global mediolateral GRFs, whereas narrow parallel squats increase ankle dorsiflexion demands and are associated with greater vertical loading asymmetry. These findings support tailoring stance width and foot rotation to target hip-dominant strength and frontal-plane control versus ankle mobility demands within lacrosse-oriented neuromuscular training.