Simple method to determine sincerity of effort during a maximal isometric test of grip strength

The purpose of this study was to establish a simple method to determine the legitimacy of a maximal voluntary grip contraction (MVGC). To achieve this, 36 subjects were randomly assigned to either a sincere (S) or faker group (F) and asked without investigator knowledge to execute either a MVGC or 75% MVGC on a specially designed grip dynamometer. The dynamometer was attached to a load cell with analog output obtained from a strip chart recorder at 50 mm X sec.-1. The force curves were evaluated empirically and also analyzed according to the following components: rate of force application (SLP), peak force (PK), average force divided by peak force (DEV) and peak force divided by body weight (WTRATIO). Average values for S and F subjects respectively were; SLP 2217 vs 1642 n X s-1, PK 499 vs 387 n, and DEV 0.91 vs 0.72. When all variable were transformed to z-scores, summed for each subject and categorized by sum into upper and lower 50% groups by gender, 87.5% of the females (N = 16) and 80% of the males (N = 20) were correctly classified as S or F subjects. Based upon a discriminant analysis performed by gender, DEV was found to be the only significant predictor for females with DEV, SLP and WTRATIO being significant predictors for the males. It was concluded that S and F subjects can be determined from the results of a maximal isometric grip strength test based upon a simple configuration analysis of an isometric force curve.