Doctor of Philosophy
Christie, Anita D
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.
Summary for Lay Audience
Mental fatigue occurs during or after sustained attention on a task and leads to declines in exercise performance. However, it is unknown how mental fatigue impacts the function of the brain, nerves and muscles, which may contribute to the declines in exercise performance. Further, it is unknown if males and females respond differently to a mentally fatiguing task, despite females often reporting greater fatigue than males. Therefore, the purpose of this dissertation was to determine the effect of mental fatigue on the signals sent from the brain and nerves to a muscle in the shin important for walking, and the ability of that muscle to contract in males and females. We also determined the impact of mental fatigue on walking and balance, and examined the relationships between mental fatigue, walking, balance, and factors which influence fatigue, such as sex, physical activity and sleep quality. The results indicate that mental fatigue did not impair muscle contraction, coordination of muscles around the shin or excitability of the pathway between the brain and muscle. When contracting at 20% of maximum, the rate of signals sent from the nerve to muscle slowed and there was greater inhibition within the brain in males in females. However, these results were not specific to mental fatigue and the changes were small. Mental fatigue also did not lead to declines in walking speed in males or females. Walking characteristics were associated with sex and current feelings of fatigue, while balance was associated with sleep quality and usual feelings of fatigue. However, these associations were small, suggesting usual and current feelings of fatigue do not greatly impact walking and balance in young adults. Further, sex, physical activity level and sleep quality were not associated with the development of mental fatigue. In summary, this dissertation suggests mental fatigue does not substantially impact signals sent from the brain and nerves to muscle, the ability of muscle to contract, walking or balance in young adult males or females. However, it does highlight the complex relationship between mental fatigue, sustained attention and exercise performance, providing several avenues for future research.
Kowalski, Katie L., "A Mechanistic View of Mental Fatigue and Motor Performance: Implications of Sex, Physical Activity and Sleep Quality" (2021). Electronic Thesis and Dissertation Repository. 8033.
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