Introduction

Unilateral strength training is becoming popular as a complement to bilateral training particularly in athletes active in sports performed primarily on one leg. Some studies have shown improved performance after unilateral compared to bilateral strength training, however the underlying cause for this improvement is unclear. The aim of this study was to compare electromyography (EMG) muscle activity in unilateral and bilateral squats performed with 80% of 1repetition maximum (RM) performed in a smith machine.

Methods

Participants in the study were 12 healthy women and men (mean age 25±2 years) with previous weight-lifting experience. EMG activity was measured during the concentric phase in the muscles vastus lateralis, biceps femoris, gluteus medius and erector spinae during A) a maximal voluntary isometric contraction (MVIC), B) 1RM squat (90 degree knee flexion) bilaterally and unilaterally, and C) 3 repetitions 80% of 1RM for both the unilateral and bilateral stance, where each squat was performed at a set speed with the aid of a metronome.

Results

EMG activities, calculated as percent of MVIC, in thigh and hip muscles (vastus lateralis, biceps femoris, gluteus medius) were significantly higher (p<0.01 for all) in the unilateral compared to the bilateral stance. The highest increase in EMG activity was in the gluteus medius where the unilateral squat elicited a 2.9 increase compared to bilateral stance. Unilateral stance muscle activation was in vastus lateralis 1.2 times higher and in biceps femoris 1.5 times higher compared to the bilateral stance. For the trunk muscle erector spinae, the opposite was apparent. EMG activity was 0.6 times lower (p<0.01) when the squat was performed unilaterally compared to bilaterally.

Discussion

Even when the load is made relative to the 1RM for each stance the muscles in especially the gluteus medius but also vastus lateralis and biceps femoris is activated to a higher degree when performed unilaterally which could be a partial explanation as to why the unilateral stance can be beneficial to include in a strength training regime despite the absolute load being lower.