Exercise-heat stress with and without water replacement alters brain structures and impairs visuomotor performance

Wittbrodt, Matthew T.; Sawka, Michael N.; Mizelle, J. C.; Wheaton, Lewis A.; Millard‐Stafford, Mindy

doi:10.14814/phy2.13805

Cited by 35 publications

(36 citation statements)

References 80 publications

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“…This is a general issue in studies with volunteering participants and there is a general underrepresentation of investigations involving females in heat-studies. However, impaired motor-cognitive performance has been reported in both those including both women and men 7,[47][48][49][50][51][52] .…”

Section: Discussionmentioning

confidence: 99%

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Piil

Christiansen

Morris

et al. 2020

Sci Rep

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Health and performance impairments provoked by thermal stress are societal challenges geographically spreading and intensifying with global warming. Yet, science may be underestimating the true impact, since no study has evaluated effects of sunlight exposure on human brain temperature and function. Accordingly, performance in cognitively dominated and combined motor-cognitive tasks and markers of rising brainstem temperature were evaluated during exposure to simulated sunlight (equal to ~1000 watt/m 2). Acute exposure did not affect any performance measures, whereas prolonged exposure of the head and neck provoked an elevation of the core temperature by 1 °C and significant impairments of cognitively dominated and motor task performances. importantly, impairments emerged at considerably lower hyperthermia levels compared to previous experiments and to the trials in the presents study without radiant heating of the head. These findings highlight the importance of including the effect of sunlight radiative heating of the head and neck in future scientific evaluations of environmental heat stress impacts and specific protection of the head to minimize detrimental effects. Approximately half of the global population live in regions where environmental heat stress is an issue that annually affects the ability to live healthy and productive lives 1,2. Negative effects range from thermal discomfort and impaired physical work capacity for healthy adults 3 to increased morbidity for workers regularly experiencing hyperthermia 1 and higher mortality for vulnerable citizens during heatwaves 4,5. While these issues are well-documented and exposure likely to be worsened by global warming, the effect of environmental heat stress on performance in cognitively dominated tasks is less clear. Intriguingly, in laboratory experiments, impairments in cognitively dominated task performance emerge only with profound hyperthermia 6-10 , whereas productivity losses in occupational settings are reported at considerably lower temperatures 1,11. The ability to maintain concentration and avoid attenuation of motor-cognitive performance is certainly of relevance for work and traffic safety as well as for minimizing the risks of making mistakes during other daily tasks. However, the lack of ecological test validity 1,12-14 as well as the low sensitivity of the stereotypical test protocols used in previous clinical or mechanistic studies in controlled indoor settings may have underestimated the impact of environmental heat stress in real-life scenarios 6-10. In particular, although laboratory-controlled environmental heat-stress studies commonly investigate or control for temperature, humidity and wind speed, solar radiation is often neglected, despite contributing a substantial heat load in outdoor settings, especially in the upright position with the human head directly exposed to solar radiation 15. Human brain function is highly dependent on a stable supply of blood glucose and oxygen, but the brain is also highly vulnerable to alterations...

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Section: Discussionmentioning

confidence: 99%

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Piil

Christiansen

Morris

et al. 2020

Sci Rep

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“…One study showed that the brain volume significantly increased after 1.5 L water consumption, compared to dehydration induced by water restriction for 16 h, among 12 healthy adults [62]. Further, a randomized controlled trial of 13 young adults, investigating the effects of exercise heat stress with and without water supplementation on brain structure and cognitive performance, reported that the brain ventricles decreased and periventricular structures, such as the cerebellum, increased after water replacement compared to dehydration [20]. Another study reported that dehydration and rehydration did not affect brain volume [63].…”

Section: Discussionmentioning

confidence: 99%

Different Amounts of Water Supplementation Improved Cognitive Performance and Mood among Young Adults after 12 h Water Restriction in Baoding, China: A Randomized Controlled Trial (RCT)

Zhang

et al. 2020

IJERPH

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Water is indispensable to keeping the functions of the human body working properly, including that of the brain. The purpose of this research was to explore the impacts of water supplementation on cognitive performance and mood, and to determine the optimum amount of water to alleviate detriments of dehydration after 12 h water restriction. A randomized controlled trial was implemented among 64 young adults from Baoding, China. Fasting overnight for 12 h, and at 8:00 a.m. on day 2, osmolality of first morning urine and blood, cognitive performance, and mood were assessed as the dehydration test. Then, participants were randomly separated into four groups: water supplementation groups (WS groups 1, 2, and 3 with 500, 200, and 100 mL purified water, respectively) and no water supplementation group (NW group). Participants in WS groups were instructed to drink the water within 10 min, while those in NW group drank no water. After 90 min, the same measurements were taken as the rehydration test. There was significant interaction between TIME and VOLUME in thirst when comparing dehydration with rehydration tests (F = 6.172, p = 0.001). Significant thirst reductions were found in WS group 1 and WS group 2 (p = 0.003; p = 0.041), and a significant increase was found in the NW group (p = 0.039). In the rehydration test, significant interactions between TIME and VOLUME were found in scores of anger, fatigue, and TMD (total mood disturbance) (F = 3.815, p = 0.014; F = 10.429, p < 0.001; F = 5.246, p < 0.001), compared to the dehydration test. Scores of anger were only decreased in WS group 2 (p = 0.025), and scores of fatigue and TMD decreased in WS group 1 and WS group 2 (all p < 0.05). Significant interaction between TIME and VOLUME was only found for operation span test scores (F = 2.816, p = 0.047), with scores being only higher in WS group 1 in the rehydration test compared to the dehydration test (p = 0.003). Comparing WS group 1 and WS group 2, scores of thirst, fatigue, and TMD did not differ significantly (p > 0.05). Water supplementation improved working memory and attenuated anger, fatigue, and TMD. A small amount of water (200 mL) was sufficient to attenuate thirst, anger, fatigue, and TMD of young adults, but the larger volume (500 mL) appeared to be necessary to improve working memory. The amount of 500 mL was the optimum volume to improve the cognitive performance and mood among young adults.

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“…The early reductions in CBF seen during strenuous exercise in the heat, with and without dehydration, have been postulated to reduce cerebral oxygenation [ 115 ]. A lower vascular and neuronal oxygenation could potentially compromise the cerebral metabolic rate for oxygen (CMRO 2 ), thereby contributing to the overall process of fatigue [ 115 ], reductions in motor output [ 116 , 117 ] and reductions in cognitive performance [ 118 – 121 ] that are magnified in hot environments and/or when dehydrated [ 118 , 122 – 124 ]. The characterisation of the CMRO 2 dynamics during exhaustive exercise is therefore a key question in integrative human physiology.…”

Section: Heat Hydration and The Brainmentioning

confidence: 99%

Heat, Hydration and the Human Brain, Heart and Skeletal Muscles

Trangmar

González‐Alonso

2019

Sports Med

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People undertaking prolonged vigorous exercise experience substantial bodily fluid losses due to thermoregulatory sweating. If these fluid losses are not replaced, endurance capacity may be impaired in association with a myriad of alterations in physiological function, including hyperthermia, hyperventilation, cardiovascular strain with reductions in brain, skeletal muscle and skin blood perfusion, greater reliance on muscle glycogen and cellular metabolism, alterations in neural activity and, in some conditions, compromised muscle metabolism and aerobic capacity. The physiological strain accompanying progressive exercise-induced dehydration to a level of ~ 4% of body mass loss can be attenuated or even prevented by: (1) ingesting fluids during exercise, (2) exercising in cold environments, and/or (3) working at intensities that require a small fraction of the overall body functional capacity. The impact of dehydration upon physiological function therefore depends on the functional demand evoked by exercise and environmental stress, as cardiac output, limb blood perfusion and muscle metabolism are stable or increase during small muscle mass exercise or resting conditions, but are impaired during whole-body moderate to intense exercise. Progressive dehydration is also associated with an accelerated drop in perfusion and oxygen supply to the human brain during submaximal and maximal endurance exercise. Yet their consequences on aerobic metabolism are greater in the exercising muscles because of the much smaller functional oxygen extraction reserve. This review describes how dehydration differentially impacts physiological function during exercise requiring low compared to high functional demand, with an emphasis on the responses of the human brain, heart and skeletal muscles.

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Exercise-heat stress with and without water replacement alters brain structures and impairs visuomotor performance

Cited by 35 publications

References 80 publications

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Direct exposure of the head to solar heat radiation impairs motor-cognitive performance

Different Amounts of Water Supplementation Improved Cognitive Performance and Mood among Young Adults after 12 h Water Restriction in Baoding, China: A Randomized Controlled Trial (RCT)

Heat, Hydration and the Human Brain, Heart and Skeletal Muscles

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