Assessing Sincerity of Effort in Maximal Grip Strength Tests

Abstract

The measurement of maximum hand grip strength in ergonomic or clinical settings has been a useful means of assessing physical characteristics, progress in rehabilitation and degree of disability in upper extremity injuries. The validity of the peak forces observed in such measurements is compromised by the requirement of subject cooperation in giving a maximum effort. Thus, an easily administered analysis of subject sincerity would improve this basic strength-testing tool. Several variables were developed for the discrimination of faking (submaximal) from sincere (maximal) grip contractions. A microcomputer- based grip force data collection system was assembled in which analog output from a Jamar hand dynamometer was sampled at 200 Hz and digitally analyzed. A total of 43 normal subjects (20 male, 23 female) were tested under sincere and faking conditions (three trials of each condition for each hand). The force-time curves of each trial were analyzed for peak and average forces and force variability. From these basic parameters five discriminator variables were developed. The frequency distribution of the sincere values for each of these variables was used to determine a criterion value for discrimination of sincere from faking trials. The five discriminators correctly detected 95.0, 92.5,100,100 and 97.5% of the male faking trials. Female faking was less successfully detected: 59.7, 52.2, 78.3, 71.7 and 87.0% correct detection resulted for the variables (with a 95% confidence level of correctly identifying sincerity). Multiple variable predictions improved the female faking detection up to 93.5% with little apparent decrement in sensitivity to sincerity identification. Thus, the analysis of force-time curve characteristics provides a readily implemented means of judging the sincerity of subject effort in measurement of maximum grip force.