Electromyographic analysis of effort in grip strength assessment

The purpose of the present research was to investigate the use of surface EMG in assessing effort while measuring grip strength with the Jamar dynamometer. We hypothesized that sincere, maximal grip contractions could be distinguished from feigned, submaximal contractions by differences in the amplitude and frequency content of the EMG, as well as by differences in force. Healthy subjects (seven men and ten women) were instructed on different trials to give a sincere (maximal, 100%) effort or a feigned (50% of maximal) effort 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, we found that the 50% efforts, compared to 100% efforts, showed, (1) lower peak force; (2) a slower rise to peak force; and (3) a different pattern of force measurements as a function of handle position. Feigned and sincere efforts also differed in the EMG. As hypothesized, amplitude was lower for 50% than 100% efforts. The frequency spectra of the EMG were obtained by Fourier analysis. The 50% efforts showed a higher frequency EMG than did the 100%. The results supported the hypothesis that surface EMG may provide a measure of effort in a grip strength task. Analysis of the EMG, in conjunction with force analysis, has the potential of being a valuable tool for the clinician needing to determine whether a patient is giving a sincere, maximal effort or is feigning.