Modification of the revised niosh lifting equation (rnle): a study of contributing factors to occupational low back pain in manufacturing industries in southern Malaysia

Occupational low back pain (LBP) is a complex pathophysiological condition within a biopsychosocial framework. In the manufacturing industry, manual material handling, especially lifting loads, poses significant ergonomic challenges and has become a key area of concern for occupational health. The Revised NIOSH Lifting Equation (RNLE) is widely used to assess the physical risks associated with these activities. This study aims to determine the prevalence of occupational LBP and identify the factors related to individual characteristics and ergonomic domains contributing to it. Additionally, this study proposes modifying the RNLE to create the Individual Lifting Equation (ILE), incorporating age, gender and body mass index (BMI) components for assessing risks associated with LBP. This cross-sectional study was conducted in three states in Malaysia, involving nine companies in the manufacturing industry and consisting of two phases. In Phase One, 772 participants from all job categories completed Malay- translated validated questionnaires which covered individual factors as well as domains of physical, cognitive, and organisational ergonomics. In Phase Two, an observational ergonomic risk assessment using the RNLE method was conducted among 165 manual lifting workers. Based on the results, the 1-year prevalence of LBP was 43% (n=334), which increased to 61% (n=470) over a lifetime. In the multivariable logistic regression model, both lifetime LBP and social support were identified as significant contributing factors to LBP, with odds ratios (ORs) of 45.54 (95% CI 25.62-80.94) and 1.81 (95% CI 1.16-2.83), respectively. Load and vertical location during lifting were significant predictors in the ILE model, with ORs of 1.09 (95% CI 1.01-1.18) and 1.01 (95% CI 1.01-1.02), respectively. At a Lifting Index (LI) cut-point of 2.0, all ILE models significantly predicted LBP. Among them, ILE Model 5, which includes age and BMI multipliers, had the highest ORs at 2.96 (95% CI 1.39-6.33), exceeding those of the core RNLE model. The model achieved an accuracy with a sensitivity of 1.00 and a specificity of 0.90. The diagnostic confidence was 73.8%. In conclusion, this study underscores the recurring pattern of LBP prevalence and identifies significant contributing factors within the individual and cognitive ergonomic domains. It also demonstrates that incorporating age and BMI multipliers into the ILE models at an LI cut-point of 2.0 yields slightly higher ORs compared to the core RNLE model, with high accuracy and diagnostic confidence suggesting that the RNLE could be modified to ILE.