Assessing sincerity of effort in maximal grip strength tests

Injuries to the upper extremities sometimes result in a loss of work capacity. One of the methods for measuring this loss of work capacity is the grip test. Such measurements may be compromised by an insincere effort (faking) by the subject. Smith et al. (Am J Phys Med Rehabil 1989;68:73-80) developed a protocol to identify sincere and faking efforts with the use of a modified dynamometer. The present investigation was designed to evaluate the applicability of the previously developed protocol to subjects with hand injuries. The investigators also compared the force-time characteristics for contractions at different percentages of maximum (100, 75, 50, and 25%). Sixty subjects (30 male and 30 female) were tested during two sessions while performing both faking and sincere efforts. The five discriminators previously developed were found to be good detectors for both noninjured and injured hands and provided the basis for cutoff values for the five discriminators. Single discriminator prediction gave at best an 85% faking detection rate (by using D3) for men and a 79.2% detection rate (by using D5) for women. Better results were obtained, when a multiple variable prediction was used. It can be concluded that the protocol developed by Smith et al. for detection of an insincere effort can be used successfully with persons who have sustained upper extremity injuries. Furthermore, sincere and faking grip strength "maxima" can be correctly identified across a wide range of applied force levels.