Regional changes in spine posture at lift onset with changes in lift distance and lift style

Study Design. Repeated measures experiment. Objective. To determine the effect of changes in horizontal lift distance on the amount of flexion, at lift onset, in different spine regions when using different lift styles. Summary of Background Data. By approximating spine bending during lifting as a pure rotation about a single revolute joint, the differential effects of task constraints and instructions on motions of different spine levels will be obscured. Methods. Eight participants lifted a 10-kg crate from the floor, 10 times at each of five distances. Participants were instructed to use freestyle (a participant's preferred lift style), squat, or stoop lift styles. Kinematic data were collected from the mid thoracic spine, lower thoracic/upper lumbar spine, mid lumbar spine, and the lower lumbar spine at lift onset. A whole spine angle was also calculated. Results. Flexion of the lower lumbar spine was not affected by lift distance and style. Differences between lift styles occurred mainly in the mid thoracic and the lower thoracic/upper lumbar regions. With increasing horizontal distance, changes in lift style occurred in the upper three spine regions. Conclusions. These results suggest that the tensile strain on tissues in the lower lumbar spine, which can be a cause of injury in lifting, was not affected by lift style or horizontal lift distance when lifting from floor level.