Postural control during one-arm support standing: EMG characterization

Electromyography (EMG) characterization was performed on the postural muscles of standing paraplegic subjects. The subjects stood (with either functional neuromuscular stimulation or long leg braces) using one arm for support and performed simple arm-raising tasks with their free arm in response to a visual cue. EMG activity of the postural muscles (wrist extensors and flexors, biceps, triceps, and anterior deltoid) was examined and latencies measured with respect to the earliest voluntary EMG activity. Reaction times to the cueing signal were longer than values reported for able-bodied standers, possibly reflecting the increased postural requirement for paraplegic standers. Muscle sequencing tended to follow a distal-to-proximal ordering, with the distal muscles exhibiting anticipatory activity. The earliest postural reactions were 200-250 ms after the cue; 50-100 ms before the onset of voluntary activity.