Introduction

In sports, force production and movement are predominantly generated in a unilateral weight-bearing stance. Therefore, unilateral resistance training may possibly elicit more sport-specific strength gains compared to traditional bilateral strength training. Hip- and trunk- muscles stabilize the pelvis and trunk to maintain proper technique and posture in resistance training and are thought to play a central role in sports performance as well as injury prevention. Hip- and trunk- muscle activity increases as the body weight balance change from a bilateral to a unilateral stance. Little research has examined the magnitude of change in muscle activation differences between bilateral and unilateral stance in lower body exercises.

Aim

The aim of this study was to examine the electromyographic (EMG) activity in hip and trunk muscles in three bodyweight exercises performed in a bilateral and a unilateral stance.

Methods

14 healthy, young adults participated in a single session, single-group, observational study. Manual muscle testing was used to attain a maximal voluntary isometric contraction (MVC) value for gluteus medius, gluteus maximus, rectus abdominis, and erector spinae. EMG measurements (4 channel ME6000, MegaWin Software, Kuopio, Finland) were taken during performance of squat, bridge, and plank exercises in both a bilateral and a unilateral stance.

Results

In all three exercises, EMG activity (presented as magnitude of change) was greater in the unilateral stance compared to the bilateral stance (p< 0.05), for the muscles gluteus medius (squat 478%, bridge 204%, plank 285%) and gluteus maximus (squat 371%, bridge 172%, plank 233%). In addition, in plank, EMG activity was greater in unilateral stance compared to the bilateral stance (p< 0.05) in rectus abdominis (120%) and erector spinae (127%). In the squat and bridge, no differences were identified in EMG activity for rectus abdominis and erector spinae between the bilateral and the unilateral stance.

Discussion

Nearly all unilateral exercises activated the hip muscles (gluteus medius, gluteus maximus) more than double compared to the same exercises performed bilaterally. In particular, gluteal muscle activity during the unilateral squat was more than 3.5 fold greater as compared to the bilateral stance. This greater magnitude of change in the unilateral squat might be explained by the single contact point with the ground in the squat, whereas the bridge and plank exercises include more ground contact points even in their unilateral stance. A unilateral training program including squat exercises might be beneficial for developing hip strength which is of great importance in sports performance.