The Perception of Fatigue and Associated Neurophysiological and Psychophysiological Effects during Sustained Physical Activity in Healthy Humans

Abstract

The perception of fatigue is a universal, debilitating psychological phenomenon. Yet, despite acknowledgement that fatigue undermines physical performance, its specific role in the regulation of physical activity has yet to be clearly defined. The presented thesis attempted to address this by examining the effect of a physically induced, perceived state of fatigue on behavioural, neurophysiological, and psychophysiological responses to sustained physical activity. Four experimental studies were conducted based on a common paradigm, designed to separate effects associated with the subjective experience of fatigue from concomitant influences of motor fatigability, examining the effects of demanding physical activity performed in the upper body on performance in non-active muscle group of the lower body. To establish the veracity of this paradigm, the first study assessed the impact of demanding physical activity in the upper body on indices of neuromuscular function in the lower body. Minimal effects were observed for the intervention, indicating that neuromuscular function in the lower limbs remained largely preserved following activity in the upper body. Subsequently, the second study examined how upper body activity influenced psychophysiological responses during a sustained contraction performed in the lower limbs. A perceived state of fatigue evoked by prior activity in the upper body was shown to indirectly limit endurance performance in the lower limbs by altering how effortful and pleasurable the task was perceived to be. Striving to replicate this effect and establish causal associations between perceptions of fatigue and the regulation of performance, the third study investigated whether the responses to sustained activity were modulated by the subjective intensity of the pre-induced state of fatigue. In addition, the association between individuals’ interoceptive ability and their perceptual and affective experience of physical activity was explored. A perceived state of fatigue was again shown to impair performance, altering perceptual (i.e. effort) and affective responses. Yet, interestingly, no differences were observed between the two experimental manipulations of fatigue. The perception of fatigue, across all conditions, was associated with a meta-awareness of interoceptive judgements. Finally, the fourth study examined how the decision to exert effort in a forced-choice task was impacted under a perceived state of fatigue. Though participants indicated no difference in choice preferences when fatigued, confidence in ones’ ability to complete chosen actions was reduced, indicating an association between fatigue and a (meta)awareness of perceived performance capacity. In conclusion, the findings of the thesis implicate the perception of fatigue as a top-down cognitive factor, associated with higher-order self-representations of physiological function and performance capacity, which influences perceptual and affective responses during sustained physical activity. Though these effects do not necessarily translate directly to changes in value-based decision-making, the perception of fatigue is identified as an important constraint limiting action.

Date of Award	2022
Original language	English
Awarding Institution	University of Brighton
Supervisor	Jeanne Dekerle (Supervisor) & Neil A. Harrison (Supervisor)