Quantification of gaps in the EMG interference pattern in chronic hemiparesis

Abstract

This study presents a quantification of the impersistence in the EMG interference pattern (IP) produced during maximal effort by patients with chronic hemiparesis. Monopolar needles were used to record from the flexor carpi radialis (FCR) and extensor carpi radialis longus (ECR) muscles of both the paretic and non-paretic sides of 19 patients with a history of unilateral CVA and 10 healthy control subjects during maximal voluntary isometric wrist flexion or extension. We found more gaps in the IP and fewer total seconds of EMG activity in paretic or control forearm muscles. The number of gaps was similar in paretic FCR and ECR, but the reduced active time in paretic ECR indicates proportionally more gaps per second of EMG activity. This method provides quantitative measures of both the lapses (gaps in the IP during maximal effort and the inability to sustain EMG activity (total seconds) during long contractions. The latter measure is sufficiently sensitive to distinguish the greater impairment of a paretic wrist extensor than a paretic wrist flexor muscle, and both may prove to be valuable for future comparisons of the severity of paresis and the progress of recovery. These results represent the first quantitative confirmation of previous qualitative descriptions of impersistent recruitment.