Neural basis of exertional fatigue in the heat: A review of magnetic resonance imaging methods

Abstract

The central nervous system, specifically the brain, is implicated in the development of exertional fatigue under a hot environment. Diverse neuroimaging techniques have been used to visualize the brain activity during or after exercise. Notably, the use of magnetic resonance imaging (MRI) has become prevalent due to its excellent spatial resolution and versatility. This review evaluates the significance and limitations of various brain MRI techniques in exercise studies-brain volumetric analysis, functional MRI, functional connectivity MRI, and arterial spin labeling. The review aims to provide a summary on the neural basis of exertional fatigue and proposes future directions for brain MRI studies. A systematic literature search was performed where a total of thirty-seven brain MRI studies associated with exercise, fatigue, or related physiological factors were reviewed. The findings suggest that with moderate dehydration, there is a decrease in total brain volume accompanied with expansion of ventricular volume. With exercise fatigue, there is increased activation of sensorimotor and cognitive brain areas, increased thalamo-insular activation and decreased interhemispheric connectivity in motor cortex. Under passive hyperthermia, there are regional changes in cerebral perfusion, a reduction in local connectivity in functional brain networks and an impairment to executive function. Current literature suggests that the brain structure and function are influenced by exercise, fatigue, and related physiological perturbations. However, there is still a dearth of knowledge and it is hoped that through understanding of MRI advantages and limitations, future studies will shed light on the central origin of exertional fatigue in the heat.

The Effect of Branched-Chain Amino Acids, Citrulline, and Arginine on High-Intensity Interval Performance in Young Swimmers

“…It has been revealed that central nervous system plays a role in the development of fatigue in repeated high-intensity exercise [9]. Several studies using functional magnetic resonance imaging have found increased activations in sensory processing and motor-related brain regions such as primary motor cortex, supplementary motor area and pre-motor cortex while performing fatiguing exercise tasks [30]. These activations suggest a greater perception of effort under fatigue and the need for higher motor output to sustain the same physical workload [31].…”

Intermittent Cooling Reduces Perceived Exertion but Has No Effect on Baseball Hitting or Defense Performance in a Hot Environment

“…The local connectivity of functional brain networks decreases in hyperthermia, which can lead to cognitive impairment (Tan et al, 2018). However, studies have obtained mixed results regarding the effect of hyperthermia in go/no-go tasks, reporting that reaction times and error rates worsened (Ando et al, 2015) or were unaffected (Shibasaki et al, 2019) after strenuous exercise in a hot environment.…”

A New Tool for Rapid Assessment of Acute Exercise-Induced Fatigue

“…Following discussions with sports experts and athletes, we combined a literature review and analysis of fatigue-related studies ( Carroll et al, 2017 ; Tan et al, 2018 ; Ratka et al, 2020 ) to determine the main research subject of the 2 types of fatigue. Comprehensively considering previous fatigue-related scales and the physiological characteristics of AEF, 14 questions were initially screened.…”

“…Fatigue originations can be classified as either peripheral or central ( Meeusen, 2014 ; Carroll et al, 2017 ; Tan et al, 2018 ; Ratka et al, 2020 ). Dysfunction of muscle contraction during exercise can induce peripheral fatigue ( O’Leary et al, 2016 ), mainly caused by consumption of energy materials, accumulation of metabolites, and material imbalance in the body ( Chang and Zhang, 2006 ).…”

“…In comparison, exercise-induced central fatigue is a protective mechanism of the central nervous system manifested as changes in thinking and consciousness to stop exercising ( Zhang, 2008 ). It is often accompanied by symptoms such as headaches, nausea, vomiting, and post-exercise cognitive impairment ( Ratka et al, 2020 ), which may be mediated by brain hypoxia ( Siebenmann and Rasmussen, 2016 ), cortical activity ( Shibuya et al, 2004 ), neurotransmitter changes ( Liu et al, 2017 ), and neuron connection changes ( Tan et al, 2018 ).…”