A Mechanistic View of Mental Fatigue and Motor Performance: Implications of Sex, Physical Activity and Sleep Quality
Abstract
Sustained attention on a task leads to the development of mental fatigue, which is characterized by increases in perceived fatigue and associated with declines in submaximal exercise performance. However, the neuromuscular mechanisms underlying the relationship between mental fatigue and declines in motor performance are unclear and it is unknown if there are sex-specific responses to mental fatigue. Accordingly, the overall objective of this dissertation was to examine sex-specific differences in the impact of mental fatigue on neuromuscular function and motor performance in young adults. This objective was achieved through three studies by investigating neuromuscular function of the tibialis anterior (electrophysiological and transcranial magnetic stimulation techniques) and walking performance before and after mental fatigue, as well as evaluating the relationships between gait characteristics, postural control and fatigue, as a state variable and trait characteristic. The influence of factors such as sex, physical activity and sleep quality on the effects of mental fatigue were also examined. Chapters 2 and 3 indicated that mental fatigue did not alter maximum force production, contractile function, co-contraction, or corticospinal excitability. Motor unit firing rate declined at 20% maximum voluntary contraction and cortical silent period duration increased in males and females, however these results were not specific to mental fatigue and the absolute differences were small. Mental fatigue did not impair single or dual task gait speed and regressions models suggested sex, physical activity level and sleep quality were not associated with the development of mental fatigue (chapter 3). Regression analyses in chapter 4 revealed models which best predicted postural control included trait fatigue, trait energy and sleep quality while models which best predicted gait characteristics included state fatigue, state energy and sex. However, the variance explained by these models was low, suggesting trait and state fatigue and energy are unlikely to greatly impact gait and postural control in young adults. In summary, this dissertation suggests mental fatigue does not substantially alter neuromuscular function or motor performance in young, healthy adult males and females. However, it highlights the complex relationship between mental fatigue, sustained attention, neuromuscular function and motor performance, providing several avenues for future research.