Real-time indicators and influence factors of muscle fatigue in push-type work

Muscle fatigue is a significant cause of musculoskeletal injury and can easily induce unsafe behaviour. Push-type work is a common type of physical work, and if not designed appropriately, may lead to muscle fatigue. Previous studies on muscle fatigue mainly focus on investigating continuous force exertion, and in most of them, a constant muscle force is assumed, thereby ignoring the fluctuations present in exertion. In this study, bolt hole drilling was chosen to represent typical push-type work, and the muscle fatigue from this work was examined. The experimental system designed in this study monitored the muscle force in real time. In the experiments, different thrust angles (15°, 45°, and 75°), different relative force values (20% MVC, 40% MVC, and 60% MVC; MVC: maximum voluntary contraction) and different working time intervals (0 s, 30 s, 60 s, and 90 s) were considered. The results demonstrate that there is a significant positive correlation between the rating of perceived exertion (RPE) and muscle force attenuation (r = 0.786, p = 0). The cubic regression model (Y = − 0.00071x³ − 0.024x² − 0.334x + 1.146, R² = 0.639) fits the data most closely. Therefore, force attenuation can be used as a real-time indicator of muscle fatigue. In addition, the relative force value and thrust angle have a significant impact on the RPE score, whereas the working time interval has no major effect on it. This study provides a new method for evaluating muscle fatigue and a basis for the design of push-type work to reduce fatigue-induced accidents and musculoskeletal injuries.