Effect of computerized instructions on measurement of lift capacity: Safety, reliability, and validity

The evaluation of lift capacity is an important part of most functional capacity evaluations. Several different methods have been developed to evaluate lift capacity in a safe, reliable, and valid manner. Isometric strength testing is one approach which has been demonstrated to be highly reliable. However, questions have been raised about the safety and validity of isometric strength testing as a predictor of "real world" lift capacity. One method to improve safety is to provide real time performance feedback so that the evaluee is able to increase psychophysical input to appropriately gauge his or her effort level. One method to improve reliability is to provide standardized instructions that are well understood by the evaluee. Both of these approaches have been utilized in the ERGOS Work Simulator, a computer-controlled multiple-task evaluation instrument that presents visual and auditory instructions to the evaluee along with "real-time" performance feedback. The safety, reliability, and validity of this computer-automated approach in comparison to an experienced human evaluator was evaluated in this research project. The results of this study demonstrate the efficacy of computerized instructions in an isometric strength testing system to achieve safe, reliable, and valid results. Intra-task variability may be improved by providing pre-test practice trials.