A Multimodal Approach to Ergonomic Assessment Fusing an IMU-Based RULA and Surface EMG System

Work-related musculoskeletal disorders (WMSDs) often arise from prolonged periods of static sitting and inadequate ergonomic posture while using a computer. This study investigates the correlation between posture-related ergonomic risk and physiological muscle strain by combining an inertial measurement unit (IMU)-based rapid upper limb assessment (RULA) system with surface electromyography (sEMG). Twenty office workers and college students performed two 30-minute typing tasks, during which five IMU sensors recorded the kinematics of their neck, trunk, and shoulder, while EMG measured activity in the sternocleidomastoid (SCM) and upper trapezius (UT) muscles. The results indicated that higher RULA neck and trunk scores were consistently associated with greater EMG amplitude, suggesting that these muscles exerted more effort to maintain poor posture for extended periods. The UT muscles exhibited significantly more activity than the SCM muscles. Muscle fatigue, evaluated via normalized median frequency (NMF) slopes, showed substantial inter-individual variability, indicating possible compensatory movements during low-level static tasks. Overall, the findings demonstrate that poor posture significantly increases muscle workload and highlight the usefulness of sensor-based systems for objective ergonomic assessment.