Simultaneous bilateral testing: validation of a new protocol to detect insincere effort during grip and pinch strength testing.

The detection of feigned weakness in hand grip strength assessment is difficult. The authors review several proposed methods and their weaknesses. A comparison of unilateral testing and simultaneous bilateral testing with the Jamar dynamometer and the Baseline pinch gauge is demonstrated as a solution. An experiment involved 100 asymptomatic subjects who were tested twice, once under instructions to give a full effort and once under instructions to feign weakness. Seven statistical criteria of noncompliance were chosen. Defining noncompliance as failing two or more of the seven criteria, 99% of the instructed noncompliant subjects were correctly classified as noncompliant. No subjects were incorrectly classified as noncompliant during instructed compliant testing. Twelve subjects failed on a single criterion. On retesting, all but one were correctly classified. One subject in the instructed noncompliant group passed all criteria. Accuracy was 99.5%, including retesting of the 12 "gray-zone" subjects.