The Reliability and Validity of a Lift Simulator and Its Functional Equivalence with Free Weight Lifting Tasks

The combination of Workers' Compensation legal claims and the enactment of the Americans with Disabilities Act (1990) has created a need for more objective and realistic trunk muscle testing. The LIDOLift (Loredan, Inc.) is a computerized dynamometer which has the capabilities to test multijoint coordinated lifting tasks in isometric, isokinetic, and isoinertial modes of operation. The calibration of the electromechanical sensors produced values greater than 0.999. In the validation of the isokinetic mode, the normalized rms error from the set velocity was less than 1% at higher set velocities, after the accelerative portion of the lift. In the technical validation of the isoinertial mode, the measured force was significantly different than the predicted force based on an isoinertial model. Consequently, the simulated mass was found to be larger than the intended mass. However, the relative difference decreased as the intended mass increased. Next, an experimental protocol was utilized to determine the validity of the isoinertial mode in the work and joint spaces. A sagittal planar dynamic biomechanical model was used to provide the basis of comparison between lifts performed with the LIDOLift and with free weights. Analyses of covariance showed statistical differences for most work and joint space variables. However, the relative difference between the two for some variables may be functionally negligible. Important guidelines for clinical protocols using the isokinetic and isoinertial modes of this simulator are delineated. Areas of technological improvement have been identified to close the gap between the simulated isoinertial condition and the free weight lifting task.