The influence of load on kinematics of computer-simulated sagittal-plane lifting.

Researchers have shown that lifting kinematics change predictably with increased load. To test whether these kinematics patterns are intrinsic or voluntary, a computer model was developed to simulate lifting in the sagittal plane. The eight-degree-of-freedom model included the ankle, knee, hip, shoulder, elbow, neck, and two back joints. Strength limits were assigned to model joints according to position-dependent average male data obtained from the literature. Using both forward and inverse dynamics approaches, the model was programmed to lift various loads while tracking lift kinematics measured from a human subject. Simulation results suggest that, contrary to common hypotheses, observed lifting patterns are not dictated by physical law (intrinsic) but are chosen for efficiency and stability (voluntary).
In this study, a method for isolating kinematic dependencies is introduced. It is anticipated that the results will help in the understanding of motion perception, lifting technique, and low-back pain.