Effects of spinal cord injury level on the activity of shoulder muscles during wheelchair propulsion: An electromyographic study

Mulroy SJ, Farrokhi S, Newsam CJ, Perry J. Effects of spinal cord injury level on the activity of shoulder muscles during wheelchair propulsion: an electromyographic study. Arch Phys Med Rehabil 2004;85:925-34. Objective To determine the influence of spinal cord injury (SCI) level on shoulder muscle function during wheelchair propulsion. Design Fine-wire electromyographic activity of 11 muscles was recorded during wheelchair propulsion. Setting Biomechanics research laboratory. Participants Convenience sample of 69 men, in 4 groups by SCI level (low paraplegia, n=17; high paraplegia, n=19; C7-8 tetraplegia, n=16; C6 tetraplegia, n=17). Interventions Not applicable. Main outcome measures Timing of muscle activity onset, cessation, and duration, and time of peak intensity for each functional group were compared with 1-way analysis of variance. Median electromyographic intensity was also compared. Results Two functional synergies were observed: push (anterior deltoid, pectoralis major, supraspinatus, infraspinatus, serratus anterior, biceps) and recovery (middle and posterior deltoid, supraspinatus, subscapularis, middle trapezius, triceps). Push phase activity began in late recovery and ceased in early to late push. Recovery phase muscles functioned from late push to late recovery. Recruitment patterns for the groups with paraplegia were remarkably similar. For subjects with tetraplegia, pectoralis major activity was significantly prolonged compared with subjects with paraplegia (P<.05). Subscapularis activity shifted from a recovery pattern in subjects with paraplegia to a push pattern in persons with tetraplegia. Conclusions Level of SCI significantly affected the shoulder muscle recruitment patterns during wheelchair propulsion. Differences in rotator cuff and pectoralis major function require specific considerations in rehabilitation program design.