Assessment of muscle electrical activity in spinal cord injury subjects during quiet standing

Disturbed motor control due to a spinal cord lesion is generally considered to be the cause of unusual standing utilized by those people suffering from spinal cord injury (SCI). Electromyographic (EMG) leg muscle activity during quiet standing was analyzed in four functional groups of SCI subjects and compared to the data of healthy people. A rating system for visual assessment of the stripchart recording was developed and its adequacy was confirmed by comparison of the rating system with computerized integrated EMG values of some of the recordings. The division of 47 subjects into functional groups was based on their ambulatory capabilities ie a non-support group, crutches, cane and walker user groups. Mean total muscle EMG activity was the highest in the group of subjects standing without support and it was significantly higher when compared to the other groups including the control group. Comparison between more and less active legs within each group showed significant differences in the non-support and crutches groups, whereas cane, walker and control groups showed nearly symmetric EMG patterns during standing. Analysis of the contribution of single muscles to the asymmetry of standing showed significantly higher activity in hamstring and triceps surae muscles than in other muscles in the non-support group. No significant differences in the activity of single muscles compared to their contralateral pair between more and less active leg were obtained in the remaining groups. It is evident, however, that different support devices used by SCI subjects greatly influence EMG patterns of postural muscles. The present findings suggest that disturbed conduction in the spinal cord is related to altered motor strategies employed by SCI subjects in attempts to perform the same volitional act as before the injury.