The effect of an exercise ball on trunk muscle responses to rapid limb movement

The use of exercise balls as an aid to facilitate improvements in posture in patients with trunk weakness is widely advocated. However, mechanisms underlying any effect on postural mechanisms have received little attention. This study compared the increases in trunk EMG activity in response to limb movement when seated on an exercise ball or on a chair in 16 healthy, moderately active subjects. At the sound of an auditory cue, the subjects carried out either hip flexion or arm flexion (unilateral or bilateral), as fast as possible, whilst sitting on an exercise ball or a standard chair. The amplitude of EMG activity was recorded from selected trunk muscles (erector spinae, external obliques, internal obliques and rectus abdominis) and either an upper limb muscle (deltoid) or a lower limb muscle (rectus femoris). There were minimal differences in amplitudes of EMG activity in any of the trunk muscles between the conditions (ball or chair) following the upper limb movements. These results suggest that there is no benefit in simple arm flexion movements whilst seated on the exercise ball in comparison to a chair. The onset and amplitude of the rectus abdominis (RA) and external obliques (EO) were significantly different between conditions in the hip flexion protocol. However, they do suggest significant benefit in decreasing RA and EO muscle activity onsets and increasing amplitude in the hip flexion condition. These results may have implications for rehabilitation of those with trunk muscle deficits such as stroke. (C) 2011 Elsevier B.V. All rights reserved.