Changes in the hemiparetic limb with training. II. EMG signal

Following a cerebro-vascular accident, motor deficits are usually associated with a selective atrophy of fast fatiguable muscle fibers. The reduction of output torque in spastic patients is considered to be caused by unfused twitches resulting from the reduction in the motor unit firing rate. To regain control of a paretic limb, these patients have to learn, through training, how to recruit an adequate number of intact motor units to generate the required functional movement. In hemiplegia, intra-subject variability makes difficult the assessment of the effects of any therapy treatments. Our objective here was thus to address the problem of the data variability and to analyze the electromyographic signal obtained from hemiplegic patients under biofeedback training. The experimental situation chosen was a very isolated but controlled motor activity (an isometric shoulder forward flexion). The results show that after training, 5 out of 11 patients could produce EMG signal from their affected deltoid whose mean value was 50% greater than before the training, while no appreciable change was observed for their unaffected deltoid. While these EMG changes on the HEMI side are correlated with greater torque output, the coefficient of correlation is slightly smaller after than before the training (r = 0.87 vs 0.89). It can be hypothesized that while the training was directed toward the deltoid, the patients in some ways developed new strategies for contracting their shoulder.