Adaptation and validation of an analytical localized muscle fatigue model for workplace tasks

Muscle fatigue is universally experienced in daily life, from recreational physical activity to the workplace. However, our ability to estimate fatigue is limited. Several attempts have been made to mathematically model the effects of fatigue, such as how long a muscle contraction may be sustained, known as `endurance time.' However, these simple models of endurance time are limited to static contractions when the body is not moving, but muscles are contracted. This research aims to advance a previously proposed analytical model of muscle fatigue to represent complex tasks such as with rest intervals and dynamic contractions. Multiple methodologies were employed to assemble data to examine the model prediction accuracy, including 1) compiling previously published data involving intermittent rest intervals (i.e., meta-analysis); 2) experimentally collecting data on intermittent fatigue for shoulder flexion as it is not well represented in the literature; and 3) experimentally collecting data on fatigue during a dynamic task for elbow flexion as dynamic tasks have been virtually ignored in fatigue literature. The results of these investigations indicate that a mathematical model of fatigue is reasonably accurate in predicting an average fatigue response across multiple subjects for both intermittent and dynamic tasks, but does not currently reflect the often wide variation in muscle fatigue development that is observed between individuals. Accordingly, this type of modeling approach may have value for general assessments of fatigue accumulation, but will need further development and modification to better represent individual characteristics.