FATIGUE AND RECOVERY DURING TASKS WITH COMPLEX FORCE PATTERNS

Abstract

The purpose of this thesis was to improve our understanding of the progression of fatigue and recovery during repetitive work and to examine selected methods for predicting fatigue. In Chapter 2, a psychophysical methodology was used to validate the Maximum Acceptable Effort (MAE) equation of Potvin (2012) at duty cycles of greater than 0.5. The results from that study were used to evaluate the MAE equation in the higher duty cycle range. In Chapter 3, the fatigue process during complex MVC-relative force profiles was examined in a repetitive handgrip task. In Chapter 4, I examined the effect of manipulating the order of presentation of various MVC-relative force levels for a repetitive thumb flexion task. Additionally, the influence of post-activation potentiation was examined by stimulating the flexor pollicis longus (FPL) at specific time points during the complex profile. In Chapter 5, Xia and Frey Law’s (2008) three-compartment model (3CMXFL) of muscle fatigue was modified to more accurately reflect physiological processes. The model, with physiological modifications (3CMGMU), as well as the original 3CM optimized for complex tasks (3CMOPT), was optimized to predict the fatigue levels from the experiments described in Chapters 3 and 4, as well as 4 other similar experimental protocols. The predicted fatigue from the 3CMXFL was also compared to the experimental data. The 3CMOPT and 3CMGMU were compared against known endurance times. The 3CMGMU is proposed as an ergonomic tool for evaluating fatigue in repetitive tasks, and the future directions for fatigue modelling and using the MAE equation for complex force-time histories are addressed. This thesis provides the first studies of fatigue accumulation during complex MVC-relative time histories. The findings from this thesis can be applied to the workplace to reduce the risk of injury as a result of muscle fatigue.