Analysis of upper-limb muscle fatigue in the process of rotary handling

Workers engaged in repetitive manual material handling (MMH) generally suffer from work-related musculoskeletal disorders (WMSDs), particularly in the arms, shoulders, neck, and waist; this significantly limits the individual's strength and ability to work. Currently, research on upper-limb injuries affecting manufacturing workers focusses on the effect of different working conditions on specific muscle fatigue. However, research on the fatigue transformation relationship among various muscles in the process of working is lacking. Therefore, the purpose of this study was to investigate the fatigue changes between the upper-limb muscles during rotary handing. In this study, 13 male subjects were studied to simulate rotating handling during the manual handling process using surface electromyography (sEMG). Handling angles of 90 degrees, 45 degrees, and 0 degrees were arranged as single variables to conduct the single-factor experiment. The sEMG of the brachioradialis, biceps brachii, trapezius, and multifidus muscle was measured during the operation. The results of this study indicate that the characteristics of muscle fatigue are different at different rotation angles: the multifidus muscle and trapezius were fatigued when the rotation was 90 degrees. Under the condition of a 45 degrees rotation, the activities of the four muscles fluctuated significantly. The slope of the median frequency of the muscles was positive, the load of the four muscles was evenly distributed, and no local fatigue was observed. Under the condition of a 0 degrees rotation, the sEMG indicated that the brachioradialis muscle was fatigued, while the other three muscles had lower loads.

Automated summary

This study found that the characteristics of muscle fatigue varied at different rotation angles, with significant fluctuations in muscle activity at a 45-degree rotation.