Effect of foot movement and an elastic lumbar back support on spinal loading during free-dynamic symmetric and asymmetric lifting exertions

The aim of this study was to assess the effect of an elastic lumbar back su pport on spinal loading and trunk, hip and knee kinematics while allowing s ubjects to move their feet during lifting exertions. Predicted spinal force s and moments about the L5/S1 intervertebral disc from a three-dimensional EMG-assisted biomechanical model, trunk position, velocities and accelerati ons, and hip and knee angles were evaluated as a function of wearing an ela stic lumbar back support, while lifting two different box weights (13.6 and 22.7 kg) from two different heights (knee and 10 cm above knee height), an d from two different asymmetries at the start of the lift (sagittally symme tric and 60 degrees asymmetry). Subjects were allowed to lift using any lif ting style they preferred, and were allowed to move their feet during the l ifting exertion. Wearing a lumbar back support resulted in no significant d ifferences for any measure of spinal loading as compared with the no-back s upport condition. However, wearing a lumbar back support resulted in a mode st but significant decrease in the maximum sagittal flexion angle (36.5 to 32.7 degrees), as well as reduction in the sagittal trunk extension velocit y (47.2 to 40.2 degrees s(-1)). Thus, the use of the elastic lumbar back su pport provided no protective effect regarding spinal loading when individua ls were allowed to move their feet during a lifting exertion.