Detecting submaximal grip exertions of variable effort by electromyography

The purpose was to determine if the surface electromyogram (EMG) would allow detection of submaximal grip exertions of variable effort. Fifteen healthy subjects were instructed on different trials to give maximal 100% efforts, fixed 50% submaximal efforts, or submaximal efforts of variable amount (30, 40, 50 or 70%) with the right hand. The subjects were tested at each of the five handle positions of the Jamar dynamometer. Surface EMG was obtained for the right palmaris longus/flexor carpi radialis muscles. Consistent with previous research was the finding that the variable effort condition yielded a bell-shaped force curve, similar to that produced by patients with true injuries. The key finding was that 100% and 50% exertions yielded linear EMG amplitude curves whereas the variable-effort exertion yielded a bell-shaped or quadratic curve. Thus, the EMG did allow for detection of the variable submaximal effort. However, the 100% and 50% exertions could not be distinguished by the average sustained force/peak force ratio. The EMG has the potential of being a valuable adjunct for the clinician needing to determine if a patient is feigning loss of grip strength.