Abstract
ckground: The effects of progressive body fluid loss on athletic and cognitive performance are known to result from exposure to environmental heat stress, morphologic factors, and limited fluid replenishment. Athletes need to restore lost body water. However, athletes may fail to maintain euhydration during exercise. This systematic review investigated hypohy- dration and fluid balance effects on an athlete’s cognitive function. Methods: The PubMed, Sports Discuss, and Ebsco databases were searched for studies reporting on hypohydration, fluid balance and heat on cognitive performance in sport. Multiple phrases including hydration, dehydration, fluid balance, mood, cognition, vigilance, decision making, and brain were explored. Participants in the studies did either receive fluid or did not receive fluid during exercise. Results: Twenty-four trials (n=493 participants) from 24 articles met the inclusion criteria. Significant hypohydration, >2% body mass loss was reported consistently in 16 publications. Five articles where hypohydration was associated with heat stress and limited fluid intake (3-5% body mass loss) impaired cognitive performance. Mood disturbance, fatigue, and ratings of perceived exertion constantly complemented hypohydration impairment on cognition. Conclusion: Findings show that hypohydration impairs cognitive performance and mood at higher levels of 3-5% body mass loss. However, sport-specific cognitive protocols of accessing hypohydration and fluid balance in individual and team sports remain equivocal. Keywords: Hypohydration; cognition; mood; fluid replenishment. DOI: https://dx.doi.org/10.4314/ahs.v22i1.45 Cite as: Dube A, Gouws C, Breukelman G. Effects of hypohydration and fluid balance in athletes’ cognitive performance: a systematic review. Afri Health Sci. 2022;22(1):367-76. https://dx.doi.org/10.4314/ahs.v22i1.45 Corresponding author: Adiele Dube, University of Zululand, Human Movement Sciences. Email: dubea2567@gmail.com Introduction Mega sporting events will continue to take place in di- verse hot geographical environment across the globe as they have been in the past and in the present. As always, hypohydration can be expected in these events. The events include the Olympic Games: Beijing 2008; Rio 2016, Tokyo 2021; World Athletics Championships Doha 2019, and Federation International Football As- sociation World Championships Qatar 2022 1,2 . With such exposure
di- verse hot geographical environment across the globe as they have been in the past and in the present. As always, hypohydration can be expected in these events. The events include the Olympic Games: Beijing 2008; Rio 2016, Tokyo 2021; World Athletics Championships Doha 2019, and Federation International Football As- sociation World Championships Qatar 2022 1,2 . With such exposure to hot environments, athletes mainly in prolonged vigorous exercise, racket and intermittent team sports experience significant and exceeding >2% body fluid loss due to thermoregulation 2,3 . Inadequate and/or no fluid loss replacement can cause endurance capacity impairment associatd with physiological and cognitive function alterations 4,5 . Indeed excessive dehy- dration impacts are major cause of concern to athletic trainers and sports medical staff. Dehydration and hypohydration deleterious effects on athletic performance and cognition have been widely researched 1,3,5 . It is well known that a 2% body mass loss can impair endurance performance in humid/hot environments 6,7 . There has been limited research on the impact of hypohydration on athlete’s cognitive perfor- mance and mood during individual and intermittent team sport 8,9 . Literature has supported that dehydration may impair cognitive performance 10- 12 and functional task 13 . However, it is known that rehydration may cause minimal or no effect on athletic, cognition and immuno- logical performance if the outcome to be assessed is in- sensitive to the modest (up to 2% of body weight) fluid losses 1, 5, 8 . Severe dehydration may disturb, aggravated fatigue, dizziness, confusion and often severe cases lead to delirium, coma and death 14-19 . Various studies have demonstrated that heat-stress and exercise-induced de- hydration did not alter cognitive performance 4, 11, 20, 21 . African Health Sciences, Vol 22 Issue 1, March, 2022 © 2022 Dube A et al. Licensee African Health Sciences. This is an Open Access article distributed under the terms of the Creative commons Attribution License (https://creativecommons.org/licenses/BY/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. African Health Sciences 367
March, 2022 © 2022 Dube A et al. Licensee African Health Sciences. This is an Open Access article distributed under the terms of the Creative commons Attribution License (https://creativecommons.org/licenses/BY/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. African Health Sciences 367
However, inconsistent conclusions exist in the current literature 4, 5, 8, 12 . Some studies have demonstrated dis- crepancies in literature may be due to task complexity, test duration, magnitude of heat stress, test combined 11, 13 . Prolonged exercising in hot, humid environments with inadequate fluid replenishment may increase core body temperature (hyperthermia) to ~4 0 C provoking athlete’s mental status that worsen in moderately and untrained athletes 4, 22, 23 . Despite that elite acclimated athletes may physiologically negotiate hyperthermic conditions, ath- letic trainers, sports scientists and sports medical staffs tirelessly work to uncover cooling techniques to curb core body temperature, delayed onset peripheral and central fatigue 4, 23- 26 . Thus, researchers have investigated dehydration, hypohydration and fluid ingestion aspects and their subsequent athletic performance effects 2,8 remains unclear. To date, no papers have reviewed and collectively discussed these aspects to equip pro- fessionals better understand impact on individual and team sport performances. Therefore, the aim of this systematic review was to summarise to summarise the literature assessing impact on hypohydration and fluid balance in relation to cognitive function in semi-pro- fessional to elite athletes exercising in humid, hot envi- ronments. Methods The study protocol was devised following the specifi- cations outlined in the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) State- ment 27 . Literature Search strategy Relevant research studies on dehydration and hypohy- dration effects on cognitive function when training in hot, humid environments identified on electronic da- tabase from 2005 until May 2020. Available literature before 2005 focused mainly on athletic performance of elite athletes. For the purpose of the current review fo- cus was on cognitive function and mood of semi-pro- fessional compared to elite athletes. The database in- clude: PubMed/Medline, Sports Discuss, and Ebsco. Keywords and terms search were hydration, athletic, exercise, mood, attention, vigilance, decision making, reaction time, sweat loss, individual/team sport, ad li- bitum, water, fluid (eg. administration, consumption, ingestion, intake, replacement, replenishment), hydra- tion (de-, eu-, hypo-, re-), each combined with cogni- tive/cognition (aspects, function), brain were explored. Searches were restricted to full-length peer-reviewed published articles in
Sports Discuss, and Ebsco. Keywords and terms search were hydration, athletic, exercise, mood, attention, vigilance, decision making, reaction time, sweat loss, individual/team sport, ad li- bitum, water, fluid (eg. administration, consumption, ingestion, intake, replacement, replenishment), hydra- tion (de-, eu-, hypo-, re-), each combined with cogni- tive/cognition (aspects, function), brain were explored. Searches were restricted to full-length peer-reviewed published articles in the English language. Unpublished experimental observations, published abstracts records that contain irrelevant terms (children, elderly, patient, disease, rat/mouse) were excluded. Twenty four orig- inal research studies involving fluid balance (water, flavoured water/ ad libitum water/ sodium chloride solution/ sports drink) not controlled by investigators, and sweat rate in athletes were included. These studies measured impact of hypohydration on cognitive per- formance. Little attention was paid to effects of physi- cal/ athletic performance considering that the data was available and up to date. Inclusion All research studies with fulfilling the following criteria were eligible for inclusion; a. All relevant South Africa and international studies. b. Studies with standardized dehydration protocol. c. Focussed on male or female humans with no underly- ing medical conditions (≥ 13 years of age). d. Fluid consumption was done in limited time ≤ 4 hours between dehydration protocol and subsequent performance test. e. A cognitive function and athletic performance out- come measured. Exclusion a. Unpublished experimental observations, published abstracts records that contain irrelevant terms (elderly, patient, disease, and rat/mouse) were excluded. b. Experimental designs without cognitive performance outcome measured. Data Extraction All published scientific research peer-reviewed articles meeting the inclusion criteria were extracted and con- sidered for the following characteristics; participant, exercise and hydration protocol, change in body mass, study findings, and study limitations. Research studies that contained more than one intervention and eligible for inclusion tested cognitive performance under two different conditions were treated as separate trials 16 . These trials derived from one study are denoted and cited by letters (a-b). Where necessary information was not given, the author considered it as unavailable. Fluid balance terminology An athlete is responsible for maintaining normal hydra- tion status (euhydration) for optimal body performance. Armstrong 28 suggests that
cognitive performance under two different conditions were treated as separate trials 16 . These trials derived from one study are denoted and cited by letters (a-b). Where necessary information was not given, the author considered it as unavailable. Fluid balance terminology An athlete is responsible for maintaining normal hydra- tion status (euhydration) for optimal body performance. Armstrong 28 suggests that change in body fluid balance African Health Sciences, Vol 22 Issue 1, March, 2022 368
is a resultant of baseline mass value compared to the individual body mass. Hydration status can be explained using terms such as; euhydration (normal baseline body water content), hypohydration (excessive body water deficit) and dehydration (progressive body water loss from normal baseline to hypohydration). Search results 567 articles were potentially relevant. After the exclu- sion of duplicates, articles published before 2005, arti- cles focusing on athletic performance, ageing, diseases and children below 13 years and review of full-text ver- sions, 24 articles were selected for review as shown in Fig 1 and Table 1 below. Fig.1. PRISMA Flow Chart of study selection process Studies identified through data base searching (n= 567) PubMed (n=240) EBSCO (n=174) Sports Discus (n=153) 232 Excluded: Reasons Not published between 2005-2020 (n=148) Abstracts (n=84) Total trials analysed (n=24) 8 studies excluded: Reasons Development in <13 yr old children (n=2) Focus on ageing (n=4) Disease (n=2) Discontinued intervention (give reasons) (n= ) Athletic performance (n= 54) Cognitive performance (n=32) Allocation Analysis Follow - u p Studies after duplicates removed (n=318) Enrollment Full Text Assessed for eligibility including reviews (n=86) Excluded: Reason Duplicates =249 Screening African Health Sciences, Vol 22 Issue 1, March, 2022369
Table 1: Summary of research studies evaluating effects hydration levels on cognitive performance Citation Participants Protocol Hydration loss levels (% ∆ body mass Fluid Type Key Findings Limitations Physiological and subjective measures Cognitive domains assessed Hyperthermia and Hypohydration effects on cognition Goodman et al. (29) N=15 12M, 3 Gender not revealed Military Defence Force 21-34yrs USA Crossover designed, 90min self- paced military march in standardised military attire in the heat with a 20kg backpack Fluid restriction and or prescribed fluid intake throughout the exercise. Cognitive test battery Envir. Conditions: 39.5-41.8℃, 28-42% RH 2.28 (HYP trial- no fluid) 0.53 (EUY trial – Ad libitum fluid) Ad libitum water HYP: ↑Core body temp. ↑HR, ↑RPE, ↑Thirst. EUY: No significant difference in core body temp, perceived thirst Information processing, memory, impulsivity, attention, and concentration, response time domains HYP: ↓working memory ↓response times ↓attention task ↓depression ↓accuracy No significant effect on immediate or delayed memory, accuracy, and response speed. Participants not blinded to hydration status Wittbrodt et al. (30) N=13 7M, 6F 19-28yrs Healthy recreationally active adults USA 2-week; Counterbalanced 150min trial (intermittent exercise protocol): Three experimental; no exercise heat stress (CON), exercise heat seat stress with fluid replacement (EUY), exercise heat stress with dehydration (DEHY), exercise heat stress without fluid replacement (HYP) Visuomotor Pacing Task (VMPT) Envir. Conditions: EUY, HYD, HYP : 45℃, 15% RH CON: 22 ℃, 30% RH 3.1 DEHY, HYP (3.3 men 3.1 women) 0.2 EUY 0.0. CON EUY, DEHY: water equivalent to sweat HYP: No fluid, only mouth rinse once per hour ↑HR, ↑Rectal temp., RPE, Thirst Visuomotor functioning, Accuracy, reaction time EUY, DEHY: Visuomotor performance impaired A significant effect on processing accuracy, and reaction time Participants not blinded to hydration status MacLeod et al. (1) N=8F 19-22yrs Healthy unacclimatized elite hockey players UK 4 experimental sessions: 50min Hockey intermittent treadmill protocol with prescribed fluid intake to replace sweat loss; ad libitum water intake, or no fluid Cognitive testing after treadmill protocol Envir. conditions: Hot; 33.2-33.4℃, 58-60% RH Moderate; 13-19℃, 51-55% RH HYP: ~2 no fluid EUY: ~ 0.0 No difference in ad water intake on moderate temp. Ad
unacclimatized elite hockey players UK 4 experimental sessions: 50min Hockey intermittent treadmill protocol with prescribed fluid intake to replace sweat loss; ad libitum water intake, or no fluid Cognitive testing after treadmill protocol Envir. conditions: Hot; 33.2-33.4℃, 58-60% RH Moderate; 13-19℃, 51-55% RH HYP: ~2 no fluid EUY: ~ 0.0 No difference in ad water intake on moderate temp. Ad libitum water ↑RPE ↑Thirst (HYP) prior to treadmill protocol No significant effect on HR and Temp (body core) Process speed, working memory, perceptive discrimination, visual scanning/ processing speed HYP: ↑Psychomotor function, visual scanning/ process speed EUY; ↑ working memory Participants not blinded to hydration status Piil et al. (13) N=139 139M 30-32yrs Recreationally active Cyprus, Denmark, Greece, Spain (Compiled in Greece) Laboratory experiment: (EUY, DEHY) Occupational study (urine sampling), 8M for laboratory experiment in an environmental chamber with fluid replacement Motor-cognitive test battery pre- & post- Envir conditions: Manufacturing; 29℃, 25% H Agriculture; 29 ℃, 55% RH Police officers; 27 ℃, 50% RH Tourism; 30 ℃, 55% RH Construction; 26 ℃, 54% RH Environmental chamber; 40℃, 25% RH ~ 2.0 (no fluid) 0.0 (fluid replacement) Water ↑RPE, ↑Core body temp., ↑Thermal comfort, ↑Thirst ↑HR Process speed, working visual scanning/ processing speed No significant effect on cognitive domains Participants unaware of the researcher’s hypothesis and naive to the purpose of the studies Van den Heuvel et al. (31) N=17 17M 25yrs Healthy, non-smoking Australia Three Passive thermal-hydration protocol (water immersion) with states and then clamped using controlled, isotonic fluid administration. Unique immersion protocol establishment in the first trial and replicated in subsequent trials averaging 185min (137-242min) Envir. Conditions: Temperate; 34-35℃, Warm water; 40-41℃ 3 and 5 (HYP) 0.0 (EUY trial) sodium chloride NaCI+ ↑HR, Thermal state, Core body temp., in HYP at 3% and 5% Visual perception, working memory ↑Decision process modified ↓Depression ↓Discriminative ability (hyperthermia) No significant effect visual and working memory following 3-5% dehydration Participants not blinded to hydration status Gamage et al. (32) N=30 30M 22yrs, elite cricketers UK Fluid restriction(4ml/kg/h) or fluid provision (12-15 ml/kg/h) during 2h of standardised cricket training Envir Conditions: Outdoors: 27.2-32.8 ℃, 66-89RH,
at 3% and 5% Visual perception, working memory ↑Decision process modified ↓Depression ↓Discriminative ability (hyperthermia) No significant effect visual and working memory following 3-5% dehydration Participants not blinded to hydration status Gamage et al. (32) N=30 30M 22yrs, elite cricketers UK Fluid restriction(4ml/kg/h) or fluid provision (12-15 ml/kg/h) during 2h of standardised cricket training Envir Conditions: Outdoors: 27.2-32.8 ℃, 66-89RH, ~2mph wind speed 3.7 fluid restriction trial 0.9 fluid provision trial Not reported Not reported Process speed, working memory, perceptive discrimination, visual scanning/ processing speed Not reported Participants not blinded to hydration status Fluid type unknown No validity or reliability testing of sport (cricket) skill Wittbrodt et al. (33) N=12 12M Recreational active USA Vigorous exercise intensity for 50mins Fluid assimilation time >50min Envir Conditions: Ambient temp 32℃, 65 RH 1.5 Water ↑ HR ↑altered skin temp. ↑ Thirst, ↑ fatigue Process speed, working memory, perceptive discrimination, visual scanning/ processing speed No effect Participants not blinded to hydration status Exercise intensity not mentioned Wilson et al. (34) N=8 8M Licensed jockeys UK Exercise for 45 minutes Fluid assimilation time ~35min 1.8 Water Not reported Response inhibition No effect Participants not blinded to hydration status Owen et al. (35) N=13 13M 22 yr olds, soccer semi- LIST protocol (90mims) with prescribed fluid intake to replace 89 sweat loss; ad libitum, water 0.3 (water intake) 1.1 (ad libitum Ad libitum water ↑ RPE (no fluid than water intake) Process speed, working memory, No effect Participants were not blinded to hydration African Health Sciences, Vol 22 Issue 1, March, 2022 370
Wilson et al. (34) N=8 8M Licensed jockeys UK Exercise for 45 minutes Fluid assimilation time ~35min 1.8 Water Not reported Response inhibition No effect Participants not blinded to hydration status Owen et al. (35) N=13 13M 22 yr olds, soccer semi- professional players UK LIST protocol (90mims) with prescribed fluid intake to replace 89 sweat loss; ad libitum, water intake, or no fluid LSST and LLSPT performed after LIST protocol Envir Conditions: 19.4℃, 59.4 RH 0.3 (water intake) 1.1 (ad libitum water) 2.5 (no fluid) Ad libitum water ↑ RPE (no fluid than water intake) ↑HR (no fluid than water intake and ad libitum water) Process speed, working memory, perceptive discrimination, visual scanning/processi ng speed No effect Participants were not blinded to hydration status MacLeod et al. (3) N=8 8F 22yr olds, Elite field hockey players UK 2-day experiment Day 1: Baseline hockey skill measurement Passive heat stress (39.9℃, 73 RH) → controlled fluid intake to induce HYPO or EUH Day 2: 60 min-hockey imitated and designed intermittent treadmill protocol Hockey skills test in a gymnasium Envir Conditions: Treadmill protocol; 33.3℃, 59 RH Gym 16.3 – 22.2℃, ~ 2 (HYP trial) Day 2: ~ 0 (EUY trial) No difference in fluid intake Replacement fluid loss (88 vs 80) % Ad libitum water ↑RPE and ↑Thirst (HYPO) prior to treadmill protocol No significant effect on HR and Temp (body core) Process speed, working memory, perceptive discrimination, visual scanning/ processing speed ↓ decision making time (skills test) ~7 slower (HYP vs EUY) prior to treadmill protocol No significant effect on decision making time post treadmill protocol Protocol, not field sport- specific but intermittent treadmill protocol Use of Day 1 passive heat stress for Day 2 trials may be invalid Participants not blinded to hydration status Hoffman et al. (36) N=10 10F 21 yr division 1 college Basketball player USA 40 min live scrimmage exercise Quick board lower body reaction agility, Dynavision D2- visual reaction time – all performed prior and post live scrimmage Envir Conditions: Indoors 22.6℃, 50.9 RH 2.3 no fluid) Not availed (water intake) Water No significant effect on
blinded to hydration status Hoffman et al. (36) N=10 10F 21 yr division 1 college Basketball player USA 40 min live scrimmage exercise Quick board lower body reaction agility, Dynavision D2- visual reaction time – all performed prior and post live scrimmage Envir Conditions: Indoors 22.6℃, 50.9 RH 2.3 no fluid) Not availed (water intake) Water No significant effect on HR and player load Psychomotor function/process speed, visual scanning/processi ng speed No significant effect on visual reaction time Participants not blinded to hydration status No trial report for ∆ body mass during water intake Cognitive tests not validated prior Brandenburg & Gaetz (37) N=12 12F 24yr Basketball Elite players Canada A descriptive study covering 2 international indoor matches Envir Conditions: 22.5 – 23.5℃ 44-50 RH 1 st match -2.1 to +5 2 nd match -2 to +0.1 Diluted ad libitum and water according to individual taste ↑ HR Process speed, working memory, perceptive discrimination, visual scanning/processi ng speed No significant effect on field goal percentage Adverse relation (goal vs body mass loss in the 2 nd match Carbohydrate has the confounding potential effect on Goal percentage No controlled trial (EUY) Ely et al. (38) N=32 32M Healthy and non-heat 3-week experiment EUY and HYP trials, 3h work-rest cycle, 4 Sodium chloride (NaCI) + water HYP (no fluid replacement) Psychomotor function/process No significant effect on mood and cognition Carbohydrate ingestion may have confounding Carvalho et al. (39) N=12 12M 14-15yr Basketball national team players Portugal 90 min training session HYP trials Basketball drills before and after training Envir Conditions: Indoors; 21.9-26.0 ℃, 48.3- 54.1 RH 2.5 (no fluid) 1.1 fluid intake) Ad libitum water HYP trial: ↑RPE in Process speed, working memory, perceptive discrimination, visual scanning/processi ng speed Not availed Participants not blinded to hydration status EUY (control) trial not available Basketball drill not validated prior Ali et al. (40) N=10 10F Soccer Premier division players New Zealand 90min LIST protocol with fluid intake (15ml/kg) or without LSPT performed before, during, and after LIST Envir Conditions Not availed 2.2 (HYP) 1.0 (EUY) Water HYP trial: ↑RPE, core temperature, HR, blood lactate
Description
The review summarizes literature on hypohydration's impact on cognitive performance in athletes.