Analysis of human muscle contractility with a microcomputer-controlled stimulus and data acquisition system

This report describes and assesses a technique to indirectly stimulate and quantify the human in vivo muscle response for clinical use. A method has been developed to isolate, stimulate, and record the flexor function of the first dorsal interosseus and first volar interosseus at the metacarpophalangeal (MCP) joint by stimulation of the ulnar nerve at the wrist. A microprocessor-based data acquisition and analysis system was built to deliver the electric stimulus and convert the muscle action potential (M-wave) and force measurements into digital form for analysis. To evaluate the technique, the twitch, paired twitch, and tetanic contractions were analyzed in 81 normal subjects. The tension developed by the youngest subjects (14 to 19 years old) was significantly less than the tension developed by subjects in the three older groups (20 to 34 years, 35 to 50 years, and 50 to 65 years); the tensions in the older groups were not significantly different from each other. Only minor gender differences were noted. This indicates that it is necessary to use age-group controls when looking for evidence of a muscle contractile abnormality in patients with neuromuscular disorders. posttetanic potentiation of the twitch was observed in all healthy subjects, and there was no evidence of an age or gender influence. The posttetanic increase in twitch tension was not associated with a prolongation of the twitch contraction time.