Electromyographic study of local and generalized muscular impairment

A study was made of a) the effects of magnitude and duration of sustained isometric muscular contractions voluntarily maintained until ‘exhaustion’ on the surface electromyogram of active and inactive muscle and b) of the residual effects of an original contraction on the EMG obtained during a succeeding contraction. It was found that the EMG progressively increases with time in both active and passive muscle during sustained contraction, the rate being proportional to magnitude of contraction, and that the initial, average and final EMG levels relate positively to contraction magnitude, while the total EMG output and duration of contraction varies inversely and exponentially with contraction magnitude. The surface EMG appears to be related to impairment through an intermediary variable, voluntary effort. Submitted on June 8, 1959