Electromyographic activity of shoulder muscles during wheelchair propulsion by paraplegic persons

Phasing and intensity of shoulder muscle activity during wheelchair propulsion were documented to identify muscles at risk for fatigue and overuse.

Electromyographic (EMG) activity of 12 muscles was recorded with wire electrodes in 17 paraplegic men during propulsion on a stationary ergometer.

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.

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).

Muscles most vulnerable for fatigue were pectoralis major, supraspinatus, and recovery muscles. Endurance training was recommended.