ELECTROMYOGRAPHIC ACTIVITY OF SHOULDER MUSCLES DURING WHEELCHAIR PROPULSION BY PARAPLEGIC PERSONS

Objective: Phasing and intensity of shoulder muscle activity during wh eelchair propulsion were documented to identify muscles at risk for fa tigue and overuse. Design and Participants: Electromyographic (EMG) ac tivity of 12 muscles was recorded with wire electrodes in 17 paraplegi c men during propulsion on a stationary ergometer. Main Outcome Measur es: Push and recovery phases of the propulsion cycle were determined w ith an instrumented pushrim. Onset and cessation of EMG were compared between muscles with a repeated measures ANOVA. Average and peak EMG i ntensity 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 ph ase 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 i n this group. Cessation occurred in late push (17% to 23% cycle) excep t in biceps brachii (8% cycle) (p < .01). The 5 recovery muscles-middl e and posterior deltoid, subscapularis, supraspinatus, and middle trap ezius-had EMG onsets in late push (17% to 26% cycle) with moderate ave rage intensities (21% to 32% MAX). These muscles had two EMG peaks (en d of push and mid-recovery). Cessation was in late recovery (82% to 91 % cycle). Conclusions: Muscles most vulnerable for fatigue were pector alis major, supraspinatus, and recovery muscles. Endurance training wa s recommended. (C) 1996 by the American Congress of Rehabilitation Med icine and the American Academy of Physical Medicine and Rehabilitation .