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.