Objective: Phasing and intensity of shoulder muscle activity during wheelchair propulsion were documented to identify muscles at risk for fatigue and overuse.
Design and participants: Electromyographic (EMG) activity of 12 muscles was recorded with wire electrodes in 17 paraplegic men during propulsion on a stationary ergometer.
Main outcome measures: Push and recovery phases of the propulsion cycle were determined with an instrumented pushrim. Onset and cessation of EMG were compared between muscles with a repeated measures ANOVA. Average and peak EMG intensity also were identified.
Results: All muscles functioned either in push or recovery phases, except supraspinatus, which displayed both patterns, and latissimus dorsi, which was inconsistent. The 6 push phase muscles--anterior deltoid, sternal pectoralis major, supraspinatus, infraspinatus, serratus anterior, and long head of biceps brachii--had onsets in late recovery (78% to 93% cycle) with peak EMG in the first 10% of the cycle. Pectoralis major and supraspinatus had the highest peak (58% and 67%MAX) and average (35% and 27%MAX) EMG intensities in this group. Cessation occurred in late push (17% to 23% cycle) except in biceps brachii (8% cycle) (p < .01). The 5 recovery muscles--middle and posterior deltoid, subscapularis, supraspinatus, and middle trapezius--had EMG onsets in late push (17% to 26% cycle) with moderate average intensities (21% to 32%MAX). These muscles had two EMG peaks (end of push and mid-recovery). Cessation was in late recovery (82% to 91% cycle).
Conclusions: Muscles most vulnerable for fatigue were pectoralis major, supraspinatus, and recovery muscles. Endurance training was recommended.