Simple And Complex Cognitive Functions Under Exertional Heat Stress

ABSTRACTHeat stress is a significant problem in the military services. This study investigated the effects of exertional heat stress on cognitive performance.Forty unacclimated male soldiers performed exertional heat stress tests in cool (20 °C) and hot environments (40 °C). Cognitive performance was assessed using a computerized battery before and immediately after tests. Physical strain in cool conditions induced mild but significant deficits in accuracy in complex tests. The number of correct answers in the Matching to Sample Visual Search was reduced (92,18% correct answers before vs. 88,64 after; p<0,05) and also in the spatial part of the Pattern and Spatial Recognition Memory Test (85,25 vs. 8,75%; p<0,05). These decreases were more pronounced in hot conditions (92,38 vs. 84,31% in before and 84,21 vs. 73,42% in the latter test; ps<0,01 and <0,001, respectively). Exertional heat stress also impaired more simple cognitive functions. A significant decrease in accuracy (95,74 vs. 93,89%) and an increase in reaction time (300,32 vs. 315,00 ms) was observed in the Reaction Time test.Strenuous physical activity in a hot environment induces mild cognitive deficits, especially in more complex tasks.

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Caffeine and Cognitive Functions in Sports: A Systematic Review and Meta-Analysis

Nutrients ◽

10.3390/nu13030868 ◽

2021 ◽

Vol 13 (3) ◽

pp. 868

Author(s):

Jorge Lorenzo Calvo ◽

Xueyin Fei ◽

Raúl Domínguez ◽

Helios Pareja-Galeano

Keyword(s):

Systematic Review ◽

Reaction Time ◽

Cognitive Performance ◽

Cognitive Functions ◽

Web Of Science ◽

Meta Analysis ◽

Caffeine Intake ◽

Inclusion Criteria ◽

Research Protocols ◽

The Relationship

Cognitive functions are essential in any form of exercise. Recently, interest has mounted in addressing the relationship between caffeine intake and cognitive performance during sports practice. This review examines this relationship through a structured search of the databases Medline/PubMed and Web of Science for relevant articles published in English from August 1999 to March 2020. The study followed PRISMA guidelines. Inclusion criteria were defined according to the PICOS model. The identified records reported on randomized cross-over studies in which caffeine intake (as drinks, capsules, energy bars, or gum) was compared to an identical placebo situation. There were no filters on participants’ training level, gender, or age. For the systematic review, 13 studies examining the impacts of caffeine on objective measures of cognitive performance or self-reported cognitive performance were selected. Five of these studies were also subjected to meta-analysis. After pooling data in the meta-analysis, the significant impacts of caffeine only emerged on attention, accuracy, and speed. The results of the 13 studies, nevertheless, suggest that the intake of a low/moderate dose of caffeine before and/or during exercise can improve self-reported energy, mood, and cognitive functions, such as attention; it may also improve simple reaction time, choice reaction time, memory, or fatigue, however, this may depend on the research protocols.

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Effects of Acclimation on Cognitive Performance in Soldiers during Exertional Heat Stress

Military Medicine ◽

10.7205/milmed.172.2.133 ◽

2007 ◽

Vol 172 (2) ◽

pp. 133-136 ◽

Cited By ~ 37

Author(s):

Sonja S. Radakovic ◽

Jelena Maric ◽

Maja Surbatovic ◽

Slavica Radjen ◽

Elka Stefanova ◽

...

Keyword(s):

Heat Stress ◽

Cognitive Performance ◽

Exertional Heat Stress

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Sex differences in response to exercise heat stress in the context of the military environment

BMJ Military Health ◽

10.1136/jramc-2019-001253 ◽

2020 ◽

pp. jramc-2019-001253 ◽

Cited By ~ 2

Author(s):

Jo Corbett ◽

J Wright ◽

M J Tipton

Keyword(s):

Sex Differences ◽

Heat Stress ◽

Ecological Validity ◽

Female Soldier ◽

Employment Standards ◽

Behavioural Factors ◽

Body Temperature Increase ◽

Hot Environments ◽

Response To Exercise ◽

The Military

Women can now serve in ground close combat (GCC) roles, where they may be required to operate alongside men in hot environments. However, relative to the average male soldier, female soldiers are less aerobically fit, with a smaller surface area (AD), lower mass (m) with higher body fat and a larger AD/m ratio. This increases cardiovascular strain, reduces heat exchange with the environment and causes a greater body temperature increase for a given heat storage, although a large AD/m ratio can be advantageous. Physical employment standards for GCC roles might lessen the magnitude of fitness and anthropometric differences, yet even when studies control for these factors, women sweat less than men at high work rates. Therefore, the average female soldier in a GCC role is likely to be at a degree of disadvantage in many hot environments and particularly during intense physical activity in hot-arid conditions, although heat acclimation may mitigate some of this effect. Any thermoregulatory disadvantage may be exacerbated during the mid-luteal phase of the menstrual cycle, although the data are equivocal. Likewise, sex differences in behavioural thermoregulation and cognition in the heat are not well understood. Interestingly, there is often lower reported heat illness incidence in women, although the extent to which this is influenced by behavioural factors or historic differences in role allocation is unclear. Indeed, much of the extant literature lacks ecological validity and more work is required to fully understand sex differences to exercise heat stress in a GCC context.

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Influence of acclimatization on serum enzyme changes in soldiers during exertional heat stress

Vojnosanitetski pregled ◽

10.2298/vsp0905359r ◽

2009 ◽

Vol 66 (5) ◽

pp. 359-364 ◽

Cited By ~ 1

Author(s):

Sonja Radakovic ◽

Jelena Maric ◽

Maja Surbatovic ◽

Nadja Vasiljevic ◽

Mladen Milivojevic

Keyword(s):

Heat Stress ◽

Stress Test ◽

Serum Concentrations ◽

Climatic Chamber ◽

Physiological Strain ◽

Physical Strain ◽

Stress Increase ◽

Wet Bulb Globe Temperature ◽

Globe Temperature ◽

Exertional Heat Stress

Background/Aim. Exertional heat stress is common problem in military services. The aim was to examine changes in serum concentrations of some enzymes in soldiers during exertional heat stress test (EHST) as well as the effects of 10-days passive or active acclimatization in climatic chamber. Methods. Forty male soldiers with high aerobic capacity, performed EHST either in cool (20 ?C, 16 ?C Wet bulb globe temperature - WBGT), or hot (40 ?C, 25 ?C WBGT) environment, unacclimatized, or after 10 days of passive or active acclimation. Physiological strain was measured by tympanic temperatures (Tty) and heart rates (HR). Concentrations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and creatine-kinase (CK) were measured in blood samples collected before and immediately after EHST. Results. Exertional heat stress test in hot conditions induced physiological heat stress (increase in Tty and HR), with significant increase in concentrations of all enzymes in unacclimatized group: ALT (42.5 ? 4.2 before vs 48.1 ? 3.75 U/L after EHST, p < 0.01), AST (24.9 ? 5.1 vs 33.4 ? 4.48 U/L, p < 0.01), LDH (160.6 ? 20.2 vs 195.7 ? 22.6 U/L, p < 0.001) and CK (215.5 ? 91.2 vs 279.1 ? 117.5 U/L, p < 0.05). In acclimatized soldiers there were no significant changes in concentrations of ALT and AST, while concentration of CK was significantly higher. Concentrations of LDH were significantly higher in all investigated groups, regardless of temperature conditions. Conclusion. In trained soldiers, 10-days passive or active acclimatization in climatic chamber can prevent increase in serum concentrations of ALT and AST, induced by exertional heat stress. Increase of serum concentrations of CK and LDH was induced by physical strain itself, with no additional effect of heat stress.

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Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

International Journal of Sport Nutrition and Exercise Metabolism ◽

10.1123/ijsnem.2019-0300 ◽

2020 ◽

Vol 30 (1) ◽

pp. 83-98 ◽

Cited By ~ 6

Author(s):

Alan J. McCubbin ◽

Bethanie A. Allanson ◽

Joanne N. Caldwell Odgers ◽

Michelle M. Cort ◽

Ricardo J.S. Costa ◽

...

Keyword(s):

Heat Stress ◽

Thermal Sensation ◽

Position Statement ◽

Fluid Replacement ◽

Population Groups ◽

Nutritional Needs ◽

And Performance ◽

Hot Environments ◽

Ultra Endurance ◽

Exertional Heat Stress

It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete’s nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.

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Caffeine and Placebo Expectation

Journal of Psychophysiology ◽

10.1027/0269-8803.21.2.91 ◽

2007 ◽

Vol 21 (2) ◽

pp. 91-99 ◽

Cited By ~ 8

Author(s):

Yunfeng Sun ◽

Yinling Zhang ◽

Ning He ◽

Xufeng Liu ◽

Danmin Miao

Keyword(s):

Blood Pressure ◽

Heart Rate ◽

Sleep Deprivation ◽

Cognitive Performance ◽

Cognitive Functions ◽

Cardiovascular Regulation ◽

Double Blind ◽

Positive Effects ◽

Pressure Tests ◽

Healthy Males

Abstract. Caffeine placebo expectation seems to improve vigilance and cognitive performance. This study investigated the effect of caffeine and placebo expectation on vigilance and cognitive performance during 28 h sleep deprivation. Ten healthy males volunteered to take part in the double-blind, cross-over study, which required participants to complete five treatment periods of 28 h separated by 1-week wash-out intervals. The treatments were no substance (Control); caffeine 200 mg at 00:00 (C200); placebo 200 mg at 00:00 (P200); twice caffeine 200 mg at 00:00 and 04:00 (C200-C200); caffeine 200 mg at 00:00 and placebo 200 mg at 04:00 (C200-P200). Participants were told that all capsules were caffeine and given information about the effects of caffeine to increase expectation. Vigilance was assessed by a three-letter cancellation test, cognitive functions by the continuous addition test and Stroop test, and cardiovascular regulation by heart rate and blood pressure. Tests were performed bihourly from 00:00 to 10:00 of the second day. Results indicated that C200-P200 and C200-C200 were more alert (p < .05) than Control and P200. Their cognitive functions were higher (p < .05) than Control and P200. Also, C200-P200 scored higher than C200 in the letter cancellation task (p < .05). No test showed any significant differences between C200-P200 and C200-C200. The results demonstrated that the combination of caffeine 200 mg and placebo 200 mg expectation exerted prolonged positive effects on vigilance and cognitive performance.

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EFFECTS OF INONIZING RADIATION CAUSED HEAT STRESS ON THE HUMAN BODY FOR STANDARD ISO 7243

Journal of Medicine and Pharmacy ◽

10.34071/jmp.2013.1.7 ◽

2013 ◽

pp. 47-57

Author(s):

Van Trong Le ◽

Thi Tuyet Mai Nguyen ◽

Thi Xuan Duyen Nguyen ◽

Ba Luan Nguyen ◽

Tuyen Pham ◽

...

Keyword(s):

Heat Stress ◽

Risk Assessments ◽

Management Systems ◽

Temperature Index ◽

Wet Bulb Globe Temperature ◽

Simple Index ◽

Simple Tool ◽

Results Management ◽

Globe Temperature ◽

Hot Environments

Objectives: Presents heat stress Standard ISO 7243, which is based upon the wet bulb globe temperature index (WBGT), and considers its suitability for use worldwide. Materials and Methods: The WBGT index are considered and how it is used in ISO 7243 and across the world as a simple index for monitoring and assessing hot environments. Results: Management systems, involving risk assessments, that take account of context and culture, are required to ensure successful use of the standard and global applicability. For use outdoors, a WBGT equation that includes solar absorptivity is recommended. A ‘clothed WBGT’ is proposed to account for the effects of clothing. Conclusion: ISO 7243 is a simple tool to assess the heat stress and may be applicated worldwide.

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The tepary bean genome provides insight into evolution and domestication under heat stress

Nature Communications ◽

10.1038/s41467-021-22858-x ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Samira Mafi Moghaddam ◽

Atena Oladzad ◽

Chushin Koh ◽

Larissa Ramsay ◽

John P. Hart ◽

...

Keyword(s):

Heat Stress ◽

Common Bean ◽

Sonoran Desert ◽

Climate Adaptation ◽

Human Consumption ◽

Disease Resistance Gene ◽

Gene Repertoire ◽

Tepary Bean ◽

Hot Environments ◽

Insight Into

AbstractTepary bean (Phaseolus acutifolis A. Gray), native to the Sonoran Desert, is highly adapted to heat and drought. It is a sister species of common bean (Phaseolus vulgaris L.), the most important legume protein source for direct human consumption, and whose production is threatened by climate change. Here, we report on the tepary genome including exploration of possible mechanisms for resilience to moderate heat stress and a reduced disease resistance gene repertoire, consistent with adaptation to arid and hot environments. Extensive collinearity and shared gene content among these Phaseolus species will facilitate engineering climate adaptation in common bean, a key food security crop, and accelerate tepary bean improvement.

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293 Predictive utility of a brief scale to identify U.S. Army Soldiers who are genetically vulnerable and resilient to sleep loss

SLEEP ◽

10.1093/sleep/zsab072.292 ◽

2021 ◽

Vol 44 (Supplement_2) ◽

pp. A117-A117

Author(s):

Janna Mantua ◽

Carolyn Mickelson ◽

Jacob Naylor ◽

Bradley Ritland ◽

Alexxa Bessey ◽

...

Keyword(s):

Decision Making ◽

Reaction Time ◽

Sleep Deprivation ◽

Cognitive Performance ◽

Response Inhibition ◽

Sleep Loss ◽

Cutoff Score ◽

Cognitive Subscale ◽

Army Soldiers ◽

Psychomotor Vigilance

Abstract Introduction Sleep loss that is inherent to military operations can lead to cognitive errors and potential mission failure. Single Nucleotide Polymorphisms (SNPs) allele variations of several genes (COMT, ADORA2A, TNFa, CLOCK, DAT1) have been linked with inter-individual cognitive resilience to sleep loss through various mechanisms. U.S. Army Soldiers with resilience-related alleles may be better-suited to perform cognitively-arduous duties under conditions of sleep loss than those without these alleles. However, military-wide genetic screening is costly, arduous, and infeasible. This study tested whether a brief survey of subjective resilience to sleep loss (1) can demarcate soldiers with and without resilience-related alleles, and, if so, (2) can predict cognitive performance under conditions of sleep loss. Methods Six SNPs from the aforementioned genes were sequenced from 75 male U.S. Army special operations Soldiers (age 25.7±4.1). Psychomotor vigilance, response inhibition, and decision-making were tested after a night of mission-driven total sleep deprivation. The Iowa Resilience to Sleeplessness Test (iREST) Cognitive Subscale, which measures subjective cognitive resilience to sleep loss, was administered after a week of recovery sleep. A receiver operating characteristic (ROC) curve was used to determine whether the iREST Cognitive Subscale can discriminate between gene carriers, and a cutoff score was determined. Cognitive performance after sleep deprivation was compared between those below/above the cutoff score using t-tests or Mann-Whitney U tests. Results The iREST discriminated between allele variations for COMT (ROC=.65,SE=.07,p=.03), with an optimal cutoff score of 3.03 out of 5, with 90% sensitivity and 51.4% specificity. Soldiers below the cutoff score had significantly poorer for psychomotor vigilance reaction time (t=-2.39,p=.02), response inhibition errors of commission (U=155.00,W=246.00,p=.04), and decision-making reaction time (t=2.13,p=.04) than Soldiers above the cutoff score. Conclusion The iREST Cognitive Subscale can discriminate between those with and without specific vulnerability/resilience-related genotypes. If these findings are replicated, the iREST Cognitive Subscale could be used to help military leaders make decisions about proper personnel placement when sleep loss is unavoidable. This would likely result in increased safety and improved performance during military missions. Support (if any) Support for this study came from the Military Operational Medicine Research Program of the United States Army Medical Research and Development Command.

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