Higher hip flexion decreases tensor fascia latae activation and increases GMed: TFL ratio during seated abduction machine

Joint position influences neuromuscular recruitment and may affect exercise prescription. This study investigated how hip flexion angle affects electromyographic (EMG) activity of the gluteus medius (GMed) and tensor fasciae latae (TFL) during machine-based seated hip abduction. Twelve recreationally trained participants performed the exercise at 45°, 90°, and 135° of hip flexion with a load corresponding to 60% of their individual six-repetition maximum (6RM). Surface EMG signals were recorded and normalized to maximal voluntary isometric contraction (%MVIC). TFL activation showed a significant angle-dependent reduction. Both peak and mean TFL EMG were significantly lower at 135° than at 45° and 90° ( p < 0.01), with no difference between 45° and 90°. In contrast, GMed activation showed fewer differences across conditions. Peak GMed EMG did not differ significantly between angles, whereas mean GMed activation was significantly lower at 135° than at 45° ( p < 0.05), with no difference between 45° and 90°. The GMed: TFL ratio was significantly higher at 135° than at both 45° and 90° ( p < 0.01). However, this increase was driven primarily by suppression of TFL activity rather than enhanced GMed activation. These findings indicate that hip flexion angle modifies the relative distribution of hip abductor muscle activity. Moderate flexion (45°–90°) maintains higher absolute GMed activation, whereas greater flexion (135°) increases relative GMed contribution by reducing TFL involvement. Adjusting hip position may therefore influence muscle recruitment patterns depending on whether the objective is to preserve absolute activation or reduce TFL dominance.