The effects of load and speed on lumbar vertebral kinematics during lifting motions: A more detailed look

In this work, we investigated the effects of load weight and movement speed on lumbar vertebral kinematics during lifting task performance, while exploring the feasibility of non-invasive in vivo measurement of vertebral movements. An experiment was conducted in which subjects performed two-handed sagittally-symmetric lifting tasks with the load weight and movement speed systematically varied. Spherical skin-surface markers were strategically placed over subjects' spinous processes and other landmarks representing major body joints. An opto-electronic motion capture system was employed to measure the lifting motions, and a novel method was developed to derive, from the acquired data, the centers of rotation (COR) and angle profiles for individual vertebrae. The angle profiles, quantifying vertebral movement patterns, were characterized by a mathematical function with kinematically meaningful parameters. Statistical analyses were then conducted to examine whether the load and speed exerted significant effects on the COR locations and movement patterns of individual lumbar vertebrae. The results suggested: (1) the COR locations were not significantly affected by the speed or load variation; (2) the movement patterns of L2-L4 vertebrae were significantly affected by the speed but not the load variation, whereas that of L5 vertebra was significantly affected by both. Findings have implications on the relation between lifting dynamics and spinal motion control, as well as on the development of more detailed and accurate biomechanical models for depicting spinal motions and quantifying low-back stress.