Significance of biomechanical and physiological variables during the determination of maximum acceptable weight of lift

The aim was to identify which biomechanical and physiological variables wer e associated with the decision to change the weight of lift during the dete rmination of the maximum acceptable weight of lift (MAWL) in a psychophysic al study. Fifteen male college students lifted a box of unknown weight at 4 .3 lifts/min, and: adjusted the weight until their MAWL was reached. Variab les such as heart rate, trunk positions, velocities and accelerations were measured during the lifting, as well as estimated spinal loading in terms o f moments and spinal forces in three dimensions using an EMG-assisted biome chanical model. Multiple logistic regression techniques identified variable s associated with the decision to change the weights up and down prior to a subsequent lift. Results indicated that heart rate, predicted sagittal lif t moment and low back disorder (LBD) risk index were associated with decrea ses in the weight prior to the next lift. Thus, historical measures of LED risk (e.g. compression, shear force) were not associated with decreases in weight prior to the next lift. Additionally, the magnitudes of the predicte d spinal forces and LED risk were all very high at the MAWL when compared w ith literature sources of tolerance as well as observational studies on LED risk. Our findings indicate that the psychophysical methodology may be use ful for the decision to lower the weight of loads that may present extreme levels of risk of LED; however, the psychophysical methodology does not see m to help in the decision to stop changing the weight at a safe load weight .