Effects of Support Surface Height on Thigh Muscle Activation During Single-Leg Squats

Purpose: This study examined the effects of the support surface height on the activation of the vastus medialis oblique (VMO), vastus lateralis (VL), and biceps femoris (BF) during single-leg squat (SLS) exercises.A height variation is proposed as a strategy to enhance knee stabilization through selective muscle activation.Methods: Forty healthy adults participated in the study.Surface electromyography (sEMG) electrodes were attached to the VMO, VL, and BF.The participants performed the SLS at three randomized support surface heights: 0 cm, 15 cm, and 25 cm after a brief practice session.Each condition was measured three times, and the average value was used for analysis.The EMG data were normalized to the maximum voluntary isometric contraction (MVIC) for each muscle.One-way repeated measures ANOVA was performed for each muscle separately to analyze the differences in muscle activation according to support surface height.Results: One-way repeated measures ANOVA revealed the significant main effects of support surface height for the vastus lateralis (VL) (F= 11.514, p< 0.001) and vastus medialis oblique (VMO) (F= 30.425, p< 0.001), but not for the biceps femoris (BF) (F= 0.638, p> 0.05).Post hoc comparisons suggested that VL and VMO activation were significantly greater at 25 cm compared to the 0 cm and 15 cm conditions (p< 0.017).No significant differences were found between the 0 cm and 15 cm conditions.BF muscle activation remained unchanged across all height conditions.Conclusion: Modifying the support surface height during SLS can selectively increase activation in specific thigh muscles.These findings have practical implications for designing targeted rehabilitation and injury prevention programs.In particular, gradually increasing the squat height may enhance the activation of the VMO and VL, contributing to improved knee joint stabilization.