Improvements for adjustment factors of REBA and RULA based on Muscle Activation Analysis of body segmental movement

The Rapid Entire Body Assessment (REBA) and the Rapid Upper Limb Assessment (RULA) are widely used in the construction sector to evaluate risks of work-related musculoskeletal disorders. However, their rule-based scoring systems often suffer from overestimation and score fluctuation due to zero-tolerance settings in adjustment factors, which fail to account for minor joint movements. This study aims to refine arm-related adjustment factors in REBA and RULA by introducing angle tolerances derived from muscle activation analysis. Surface electromyography (sEMG) and joint angle data were collected from 25 participants as they performed three body segmental movements corresponding to REBA/RULA adjustment factors: arm abduction, wrist deviation, and wrist twisting. The findings show that, first, a 0° tolerance is unsuitable as an adjustment factor boundary because of small but consistent movements in the shoulder and wrist joints at motion onset. Second, inter-individual variability in maximum wrist deviation and twisting angles requires normalization to derive general angle tolerances. Third, joint tolerances are defined by the endurance limit of 10% maximal voluntary isometric contraction (%MVC). These findings advance adjustment factors of REBA/RULA from a zero-tolerance scoring system to a kinematic–physiological framework by introducing sEMG-based angle tolerances. Embedding these tolerances into the existing REBA/RULA framework preserves the original angle-based assessment workflow, while effectively mitigating risk overestimation and score instability in practical applications. Moreover, this integration enhances the adaptability of REBA/RULA to advanced motion detection technologies. Future work will extend this approach by incorporating additional body segmental movements and investigating weight-bearing tasks. • Advanced technology based REBA/RULA overestimates risks due to postural sway • Postural sway is consistently observed during neutral posture maintenance • Joint angle tolerances enhance REBA/RULA by addressing rigid adjustment factors • SEMG provides biomechanical insights, supplementing kinematic analysis in REBA/RULA • Quantified body segmental movement-incorporated REBA/RULA were proposed.