Effects of abdominal muscle fatigue on anticipatory postural adjustments associated with arm raising

Anticipatory postural adjustments (APAs) are postulated to ameliorate the effects of the disturbance to posture caused by voluntary movement. The primary hypothesis tested in our study was that the magnitude of anticipatory trunk muscle activity is altered by abdominal muscle fatigue. A subsidiary aim of the present study was to examine the directional nature of APAs and use this information to elucidate the central or peripheral nature of changes in postural muscle activity associated with abdominal muscle fatigue. The present study was a within subject design, where abdominal muscle fatigue was induced by a static abdominal curl. Surface EMG was used to assess postural muscle activity in the following trunk muscles; rectus abdominis, erector spinae and internal oblique. Following abdominal muscle fatigue, the magnitude of muscle activity during APAs was significantly reduced by 20% in both the rectus abdominis (fatigued muscle) and the erector spinae (not fatigued) indicating a central rather than peripheral fatigue effect on muscle activity. Abdominal muscle fatigue also induced a 30% increase in the baseline muscle activity of the internal oblique. The changes in magnitude of APA muscle activity may reflect a change in system gain or a change in postural control perhaps related to a change in perceived postural stability. An increase in baseline muscle activity in the internal oblique may compensate partially for the reduction in APAs.