Recruitment and termination of electromyographic activity in the hemiparetic forearm

Motor unit control measured by timed recruitment and termination of intramuscular electromyographic (EMG) activity provides muscle-specific quantification of deficits of the arm in chronic hemiparesis. Latencies to recruitment and termination of EMG activity of flexor carpi radialis and extensor carpi radialis longus were recorded from nine stroke patients and five age- and sex-matched control subjects, in response to buzzer signals, during maximal isometric wrist flexion and extension. Both agonist and antagonist recruitment times were slower in paretic than in control forearms (p less than .01). Termination of EMG activity occurred earlier in paretic forearms, primarily because of inability to maintain a prolonged muscular contraction. The effects of the variable lengths of testing trials reinforced these conclusions. The paretic extensor carpi radialis longus showed the greatest impairment with a very long latency to contract, and frequent failure to maintain a contraction. This study presents a new method of quantifying a common clinical problem in rehabilitation medicine.