Effects of lift style and dynamics during repetitive lifting

Proposes that, in a dynamic lifting task, individuals adjust their lifting style to minimize a cost function involving some combination of work performed and forces generated in the spine. This proposal is to be evaluated with data previously obtained in a large experimental study of low-back pain patients before and after treatment. Because of limitations in the data collected for this study, an approximate three-segment model of the body is to be used to estimate the total work performed per lift and the moment generated at the hip, using as inputs the hip and knee angles as functions of time during the lift and the patient's height and weight. Simulation results are presented to illustrate the effects of lift type and dynamics on work and hip moment. The model then is applied to a sample of 15 patients and 15 controls. The results show that controls lift heavier loads than the patients do, but at a cost of incurring higher moments at the hip. Assuming that these moments reflect greater forces in the spine, the results suggest that controls are willing to tolerate greater spinal forces than patients in order to perform efficient lifts.