COORDINATION BETWEEN THE LUMBAR SPINE LORDOSIS AND TRUNK ANGLE DURINGWEIGHT-LIFTING

Objective. To analyze the coordination of the lumbo-sacral angle (lumb ar spine lordosis) and the trunk inclination during lifting of differe nt loads. Study design. Kinematic data of spine motion were analyzed. The parameters characterizing the relationships between the lordosis a nd the trunk inclination angle were estimated. Background. The shape o f the spine has been analyzed mostly for static or quasi-static condit ions. The parameters relating the lumbar spine lordosis and trunk incl ination in dynamics have not been analyzed. Methods. Healthy subjects performed unconstrained weight lifts from ground to mid-thigh level. K inematic data were derived from the tracking of markers (light-emitted diodes) placed over the spine and pelvis using an OPTPTRAK system. Th e relationship between lordosis and trunk inclination was analyzed. Re sults. The relationship between lumbar spine curvature (lumbo-sacral a ngle or lordosis) and trunk inclination during weight lifting was desc ribed by an exponential function with three parameters. These were the lordosis extremes associated with the horizontal and vertical positio ns of the trunk and the trunk inclination when lordosis equals zero. T he absolute value of the lordosis angle decreases at the onset of the extension phase of lifting when the load increases, implying active re action 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 f reedom of the spine, providing an inter-joint synergy.