LOCALIZED MUSCULAR FATIGUE DURATION, EMG PARAMETERS AND ACCURACY OF RAPID LIMB MOVEMENTS

While much is known about the physiological basis of local muscular fa tigue, little is known about the kinematic and electromyographic (EMG) consequences of brief fatiguing isometric contractions. Five male sub jects performed a horizontal elbow flexion-extension reversal movement over 90 degrees in 250 ms to reversal before and after one of five si ngle maximal isometric elbow flexions ranging in duration from 15-120 s. Surface EMG signals were recorded from the biceps brachii, the long head of the triceps, the clavicular portion of the pectoralis major, and the posterior deltoid. Spatial and temporal errors were computed f rom potentiometer output. During the fatiguing bouts, maximum voluntar y force dropped linearly an average of 4% in the 15 s condition and 58 % in the 120 s condition relative to maximum force. The associated bic eps rectified-integrated EMG signal increased from the onset of each f atigue bout for 15-30 s, then decreased over the remainder of the long er bouts. Following the fatigue bout, subjects undershot the target di stance on the first movement trial in all conditions. Following short fatigue durations (i.e. 15-30 s), the peak biceps EMG amplitude was di srupted and movement velocity decreased, but both measures recovered w ithin seconds. As fatigue duration increased, progressive decreases in peak velocity occurred with increased time to reversal, reduced EMG a mplitude, and longer recovery times. However, the relative timing of t he EMG pattern was maintained suggesting the temporal structure was no t altered by fatigue. The findings suggest that even short single isom etric contractions can disrupt certain elements of the motor control s ystem.