This study investigated the effects of trunk forward lean angle and contralateral load on gluteus medius muscle activity during single-leg squat performance in healthy adult males.
Twenty healthy male participants in their twenties without knee pain w...
This study investigated the effects of trunk forward lean angle and contralateral load on gluteus medius muscle activity during single-leg squat performance in healthy adult males.
Twenty healthy male participants in their twenties without knee pain were included in this study. All participants performed single-leg squats under six randomized conditions combining three trunk forward lean angles (0°, 20°, and 40°) and two contralateral load conditions (with and without contralateral load). Muscle activity was measured using surface electromyography for the gluteus medius, gluteus maximus, biceps femoris, rectus femoris, and lumbar erector spinae. The collected signals were processed using root mean square (RMS) and normalized to %MVIC (maximum voluntary isometric contraction). Data were analyzed using two-way repeated measures ANOVA, and simple main effects analysis with Bonferroni correction was performed for significant interaction effects.
The results showed significant interaction effects between trunk forward lean and contralateral load on the gluteus medius, gluteus maximus, and biceps femoris, with the gluteus medius exhibiting the greatest and most consistent response to both variables. Additionally, the gluteus medius showed the highest muscle activity under the condition combining a 40° trunk forward lean with contralateral load. The main effect of trunk forward lean was significant for the gluteus medius, gluteus maximus, biceps femoris, rectus femoris, and erector spinae, while the main effect of contralateral load was significant for the gluteus medius, gluteus maximus, biceps femoris, and erector spinae.
These findings suggest that increased trunk forward lean and the application of contralateral load effectively increase gluteus medius muscle activity during the single-leg squat, with the highest activity observed when both conditions are combined. Therefore, applying trunk forward lean and contralateral load during single-leg squat exercises may be clinically useful as a strategy for strengthening the gluteus medius.