Biomechanical Assessment of the NIOSH Lifting Equation in Asymmetric Load-Handling Activities Using a Detailed Musculoskeletal Model.

OBJECTIVE: To assess adequacy of the National Institute for Occupational Safety and Health (NIOSH) Lifting Equation (NLE) in controlling lumbar spine loads below their recommended action limits during asymmetric load-handling activities using a detailed musculoskeletal model, that is, the AnyBody Modeling System.

BACKGROUND: The NIOSH committee employed simplistic biomechanical models for the calculation of the spine compressive loads with no estimates of the shear loads. It is therefore unknown whether the NLE would adequately control lumbar compression and shear loads below their recommended action limits during asymmetric load-handling activities.

METHOD: Twenty-four static stoop lifting tasks at different load asymmetry angles, heights, and horizontal distances were performed by one normal-weight (70 kg) and one obese (93 kg) individual. For each task, the recommended weight limit computed by the NLE and body segment angles measured by a video-camera system (VICON) were prescribed in the participant-specific models developed in the AnyBody Modeling System that estimated spinal loads.

RESULTS: For both individuals, the NLE adequately controlled L5-S1 loads below their recommended action limits for all activities performed in upright postures. Both individuals, however, experienced compressive and/or shear L5-S1 loads beyond the recommended action limits when lifting was performed near the floor with large load asymmetry.

CONCLUSION: The NLE failed to control spinal loads below the recommended limits during asymmetric lifting tasks performed near the floor.

APPLICATION: The NLE should be used with caution for extreme tasks involving load handling near the floor with large load asymmetry.