VOLUNTARY CONTROL OF SUBMAXIMAL GRIP STRENGTH

Stokes (J Occup Med; 1983; 25: 683-684) proposed that feigned weak hand grip can be distinguished from sincere efforts by examining force measurements for the different handle positions of the Jamar hand dynamometer. Sincere efforts yield a curvilinear relationship between grip force and handle position; feigned efforts yield a horizontal, linear relationship. The purpose of the present set of three experiments was to investigate the degree of control normal subjects have over submaximal effort and their ability to feign weakened grip. In Experiment 1 we found that subjects instructed to exert a specific amount of submaximal effort (50%) did not produce a response pattern of grip force consistent with Stokes' hypothesis. In Experiment 2 we found a linear relationship between the degree of submaximal effort and grip force for efforts of 30, 50, 70, and 90% of maximal effort. In Experiment 3 we found that subjects, with proper instruction as to the amount of effort to exert, can produce feigned submaximal efforts similar to the sincere, maximal efforts of injured people. Simple maximal grip force measurements are insensitive to the different motor strategies used in maximal and submaximal efforts and may provide little evidence for the detection of feigning.