Right shoulder complex muscles of nondisabled, paraplegic, and quadriplegic subjects were monitored with electromyography (EMG) during standardized wheelchair ambulation. It was shown that wheelchair ambulation required the recruitment of large amounts of available motor units in spinal cord–injured persons. Motor unit recruitments differed for the groups: recruitment was minimal for the nondisabled subjects, moderate for paraplegics, and often maximal for quadriplegics. In addition, large intra- and intergroup variabilities were found in the pattern of muscle recruitment during the standardized wheelchair ambulation movement.

The high variability shown in the muscle recruitment patterns of the normal individuals was unexpected, because the ambulation movement had been standardized as much as possible. The technique used to monitor muscle activity in this study reflects an example of how EMG can be employed to analyze activity during a movement. Using this technique one can objectively determine if assumptions about what is occurring in a muscle group during activity are correct.