Revised NIOSH Lifting Equation May generate spine loads exceeding recommended limits

• Recommended weight limits (RWL) were calculated by the NIOSH Equation for 50 lifts.
• The RWL were input in a detailed biomechanical model to estimate spine compression.
• The estimated compression was compared with the 3400 N limit recommended by NIOSH.
• Predicted compression exceeded the NIOSH limit for tasks involving trunk flexion.
• Caution is needed when assessing risk of injury to the spine by the NIOSH Equation.

The 1991 NIOSH Lifting Equation (NLE) is widely used to assess the risk of injury to spine by providing estimates of the recommended weight limit (RWL) in hands. The present study uses the predictive equations developed based on a detailed trunk musculoskeletal biomechanical model to verify whether the RWL generates L5-S1 loads within the limits (e.g., 3400 N for compression recommended by NIOSH and 1000 N for shear recommended in some studies). Fifty lifting activities are simulated here to evaluate the RWL by the NLE and the L5-S1 loads by the predictive equations. In lifting activities involving moderate to large forward trunk flexion, the estimated RWL generates L5-S1 spine loads exceeding the recommended limits. The NIOSH vertical multiplier is the likely cause of this inadequacy; a revised multiplier accounting for the trunk flexion angle is hence needed. The use of a fixed 3400 N compression limit is also questioned.Relevance to industryErgonomist and occupational health practitioners are advised to use the NLE along with the predictive equations of the spine loads proposed in this study when evaluating the risk of injury to the spine in lifting activities particularly those involving moderate to large trunk flexion.