Electromyogram, force and relaxation time during and after continuous electrical stimulation of human skeletal muscle in situ.

A technique for recording the surface electromyogram (e.m.g.) simultaneously with electrical stimulation of human skeletal muscle is described. During a fatiguing electrical stimulation the e.m.g. amplitude and force decreased in the same proportion. During recovery the e.m.g. was quickly normalized whereas force remained at a reduced level. Relaxation time increased during the stimulation and helps substantially in keeping up tension during a fatiguing contraction. In the recovery phase the rapid normalization of relaxation time counteracts recovery of tension. It is concluded that e.m.g. measurements alone can be misleading as an index of contraction force and that muscular fatigue during electrical stimulation can be attributed to excitation failure only to a lesser extent.