Trunk muscle responses following unpredictable loading of an abducted arm

This study investigated if asymmetry exists in the responses of trunk muscles to a perturbation of the trunk induced by loading of an outstretched arm. Nineteen healthy right-handed subjects were recruited into the study. Electromyographic recordings were made from trunk muscles (erector spinae and rectus abdominus) and upper limb muscles (deltoid). A weight was dropped into a receptacle held out laterally by the subjects. The perturbation induced a rise in EMG activity in the deltoid at a latency which was not different between the dominant and non-dominant arms. It also induced a rise in EMG activity in the contralateral trunk muscles. Although not significantly different, there was a trend for the responses from the right trunk to be longer than those from the left trunk. Furthermore, there were higher levels of EMG activity in the trunk muscles opposite the dominant arm than those in the trunk muscles opposite the non-dominant arm. This study reveals a pattern of trunk muscle activation following movement in the arm induced by loading of an outstretched hand that is different on the side of the back opposite the dominant arm than on the side of the back opposite the non-dominant arm. These results may have implications in terms of mechanisms contributing to low back pain and further work is warranted to examine these responses in left-handed individuals.