Coordination between the lumbar spine lordosis and trunk angle during weight lifting

Objective. To analyze the coordination of the lumbo-sacral angle (lumbar spine lordosis) and the trunk inclination during lifting of different loads. Study design. Kinematic data of spine motion were analyzed. The parameters characterizing the relationships between the lordosis and the trunk inclination angle were estimated. Background. The shape of the spine has been analyzed mostly for static or quasi-static conditions. The parameters relating the lumbar spine lordosis and trunk inclination in dynamics have not been analyzed. Methods. Healthy subjects performed unconstrained weight lifts from ground to mid-thigh level. Kinematic data were derived from the tracking of markers (light-emitted diodes) placed over the spine and pelvis using an OPTPTRAK system. The relationship between lordosis and trunk inclination was analyzed. Results. The relationship between lumbar spine curvature (lumbo-sacral angle or lordosis) and trunk inclination during weight lifting was described by an exponential function with three parameters. These were the lordosis extremes associated with the horizontal and vertical positions of the trunk and the trunk inclination when lordosis equals zero. The absolute value of the lordosis angle decreases at the onset of the extension phase of lifting when the load increases, implying active reaction of musculosceletal system to increasing load. Conclusions. The changes in the lordosis and trunk inclination are strictly correlated implying that the nervous system actively coordinates the degrees of freedom of the spine, providing an inter-joint synergy.