The effects of exercise, heat, cooling and rehydration strategies on cognitive function in football players

The effect of menthol rinsing before intermittent exercise on physiological, physical, and thermo-behavioral responses of male football referees in hot and humid environment

Introduction

In the current experiment, we aimed to evaluate whether eliciting pre-exercise non-thermal cooling sensations would alter perceptual measures, and physical and physiological responses in football referees.

Methods

Nine highly trained male football referees undertook two 45-minute intermittent exercise protocols in hot and humid conditions (34.2 ± 0.6°C, 62.5 ± 1.0% relative humidity). In a randomized counterbalanced crossover design, 1 of 2 beverages were given before the warm-up: a 0.01% menthol solution or a placebo noncaloric solution. Physical performance was quantified as total distance covered in each of the three 15-minute exercise blocks. Core temperature, heart rate, thermal sensation and thermal comfort were measured at rest and after each exercise block.

Results

No changes were observed between trials and over time for distance covered. No main effect of mouth rinse was observed for core temperature and heart rate, but both increased over time in all conditions (P < 0.001). Thermal sensation and thermal comfort were significantly improved with menthol after mouth-rinsing (P < 0.05), but with no differences at any other time-point.

Discussion

These results indicate that non-thermal cooling oral stimuli provide immediate behavioral changes but may not influence physiological or physical responses in football referees, during intermittent exercise in hot and humid environments.

Clinical Trial Registration

www.clinicaltrials.gov, identifier NCT05632692.

Continuous Monitoring of Interstitial Fluid Glucose Responses to Endurance Exercise with Different Levels of Carbohydrate Intake

We compared the 24 h changes in interstitial fluid glucose concentration (IGC) following a simulated soccer match between subjects consuming a high-carbohydrate (HCHO; 8 g/kg BW/day) diet and those consuming a moderate-carbohydrate (MCHO; 4 g/kg BW/day) diet. Eight active healthy males participated in two different trials. The subjects were provided with the prescribed diets from days 1 to 3. On day 3, the subjects performed 90 min (2 bouts × 45 min) of exercise simulating a soccer match. The IGC of the upper arm was continuously monitored from days 1 to 4. No significant difference in the IGC was observed between trials during exercise. The total area under the curve (t-AUC) value during exercise did not significantly differ between the HCHO (9719 ± 305 mg/dL·90 min) and MCHO (9991 ± 140 mg/dL·90 min). Serum total ketone body and beta-hydroxybutyrate concentrations were significantly higher in the MCHO than in the HCHO after a second bout of exercise. No significant differences in the IGC were observed between trials at any time point during the night after exercise (0:00-7:00). In addition, t-AUC value during the night did not significantly differ between the HCHO (32,378 ± 873 mg/dL·420 min) and MCHO (31,749 ± 633 mg/dL·420 min). In conclusion, two days of consuming different carbohydrate intake levels did not significantly affect the IGC during a 90 min simulated soccer match. Moreover, the IGC during the night following the exercise did not significantly differ between the two trials despite the different carbohydrate intake levels (8 vs. 4 g/kg BW/day).

Core Body Temperatures in Intermittent Sports: A Systematic Review

BACKGROUND

Hyperthermia (and associated health and performance implications) can be a significant problem for athletes and teams involved in intermittent sports. Quantifying the highest thermal strain (i.e. peak core body temperature [peak Tc]) from a range of intermittent sports would enhance our understanding of the thermal requirements of sport and assist in making informed decisions about training or match-day interventions to reduce thermally induced harm and/or performance decline.

OBJECTIVE

The objective of this systematic review was to synthesise and characterise the available thermal strain data collected in competition from intermittent sport athletes.

METHODS

A systematic literature search was performed on Web of Science, MEDLINE, and SPORTDiscus to identify studies up to 17 April 2023. Electronic databases were searched using a text mining method to provide a partially automated and systematic search strategy retrieving terms related to core body temperature measurement and intermittent sport. Records were eligible if they included core body temperature measurement during competition, without experimental intervention that may influence thermal strain (e.g. cooling), in healthy, adult, intermittent sport athletes at any level. Due to the lack of an available tool that specifically includes potential sources of bias for physiological responses in descriptive studies, a methodological evaluation checklist was developed and used to document important methodological considerations. Data were not meta-analysed given the methodological heterogeneity between studies and therefore were presented descriptively in tabular and graphical format.

RESULTS

A total of 34 studies were selected for review; 27 were observational, 5 were experimental (2 parallel group and 3 repeated measures randomised controlled trials), and 2 were quasi-experimental (1 parallel group and 1 repeated measures non-randomised controlled trial). Across all included studies, 386 participants (plus participant numbers not reported in two studies) were recruited after accounting for shared data between studies. A total of 4 studies (~ 12%) found no evidence of hyperthermia, 24 (~ 71%) found evidence of 'modest' hyperthermia (peak Tc between 38.5 and 39.5 °C), and 6 (~ 18%) found evidence of 'marked' hyperthermia (peak Tc of 39.5 °C or greater) during intermittent sports competition.

CONCLUSIONS

Practitioners and coaches supporting intermittent sport athletes are justified to seek interventions aimed at mitigating the high heat strain observed in competition. More research is required to determine the most effective interventions for this population that are practically viable in intermittent sports settings (often constrained by many competing demands). Greater statistical power and homogeneity among studies are required to quantify the independent effects of wet bulb globe temperature, competition duration, sport and level of competition on peak Tc, all of which are likely to be key modulators of the thermal strain experienced by competing athletes.

REGISTRATION

This systematic review was registered on the Open Science Framework ( https://osf.io/vfb4s ; https://doi.org/10.17605/OSF.IO/EZYFA , 4 January 2021).

Higher operating theatre temperature during burn surgery increases physiological heat strain, subjective workload, and fatigue of surgical staff

Raising the ambient temperature of the operating theatre is common practice during burn surgeries to maintain the patient's core body temperature; however, the effects of operating in the heat on cognitive performance, manual dexterity, and perceived workload of surgical staff have not been assessed in a real-world context. Therefore, the aim was to assess the real-time impact of heat during burn surgeries on staff's cognitive function, manual dexterity, and perceptual measures (workload, thermal sensation, thermal comfort, perceived exertion, and fatigue) and physiological parameters (core temperature, heart-rate, fluid loss, and dehydration). Ten burn surgery staff members were assessed in CON (24.0±1.1°C, 45±6% relative humidity [RH]) and HOT (30.8±1.6°C, 39±7% RH) burn surgeries (average 150 min duration). Cognitive performance, manual dexterity, and perceptual measures were recorded pre- and post-surgery, while physiological parameters were recorded throughout surgery. HOT conditions did not significantly affect manual dexterity or cognitive function (p > .05), however HOT resulted in heat strain (increased heart-rate, core temperature, and fluid loss: p < .05), and increased subjective workload, discomfort, perceived exertion, and fatigue compared to CON conditions (p < .05). Cognitive function and manual dexterity were maintained in hot conditions, suggesting that operating in approximately 31°C heat is a safe approach for patient treatment. However, job burnout, which is positively correlated with perceived workload, and the impact of cumulative fatigue on the mental health of surgery staff, must be considered in the context of supporting an effective health workforce.

The effectiveness of heat preparation and alleviation strategies for cognitive performance: A systematic review

A range of occupational and performance contexts (e.g. military personnel operations, emergency services, sport) require the critical maintenance of cognitive performance in environmentally challenging environments. Several reviews exist which evaluate the effectiveness of heat preparation strategies to facilitate physical performance. To date, no review has explored the usefulness of heat preparation strategies for cognitive performance. Therefore, this systematic review aimed to evaluate a range of interventions for the maintenance of cognitive performance, during or following active or passive heat exposure. Studies to be included were assessed by two authors reviewing title, abstract, and full-text. Forty articles were identified which met the inclusion criteria. Interventions were categorised into chronic (i.e. acclimation/acclimatisation) and acute strategies (i.e. hydration, cooling, supplementation, psychological). The results indicate that medium-term consecutive heat acclimation may mitigate some cognitive deficits under heat stress, although heat acclimation effectiveness could be influenced by age. Further, pre-cooling appears the most effective cooling method for maintaining cognitive performance under heat stress, although results were somewhat ambiguous. The hydration literature showed that the most effective hydration strategies were those which individualised electrolyte fortified fluid volumes to match for sweat loss. Limited research exploring psychological interventions indicates that motivational self-talk could be facilitative for maintaining cognitive skills following exercise in hot conditions. These findings can be used to help inform strategies for maintaining critical cognitive and decision-making skills in hot environments.

Performance effects of internal pre- and per-cooling across different exercise and environmental conditions: A systematic review

Exercise in a hot and humid environment may endanger athlete's health and affect physical performance. This systematic review aimed to examine whether internal administration of ice, cold beverages or menthol solutions may be beneficial for physical performance when exercising in different environmental conditions and sports backgrounds. A systematic search was performed in PubMed, Web of Science, Scopus and SPORTDiscus databases, from inception to April 2022, to identify studies meeting the following inclusion criteria: healthy male and female physically active individuals or athletes (aged ≥18 years); an intervention consisting in the internal administration (i.e., ingestion or mouth rinse) of ice slush, ice slurry or crushed ice and/or cold beverages and/or menthol solutions before and/or during exercise; a randomized crossover design with a control or placebo condition; the report of at least one physical performance outcome; and to be written in English. Our search retrieved 2,714 articles in total; after selection, 43 studies were considered, including 472 participants, 408 men and 64 women, aged 18-42 years, with a VO2max ranging from 46.2 to 67.2 mL⋅kg-1⋅min-1. Average ambient temperature and relative humidity during the exercise tasks were 32.4 ± 3.5°C (ranging from 22°C to 38°C) and 50.8 ± 13.4% (varying from 20.0% to 80.0%), respectively. Across the 43 studies, 7 exclusively included a menthol solution mouth rinse, 30 exclusively involved ice slurry/ice slush/crushed ice/cold beverages intake, and 6 examined both the effect of thermal and non-thermal internal techniques in the same protocol. Rinsing a menthol solution (0.01%) improved physical performance during continuous endurance exercise in the heat. Conversely, the ingestion of ice or cold beverages did not seem to consistently increase performance, being more likely to improve performance in continuous endurance trials, especially when consumed during exercises. Co-administration of menthol with or within ice beverages seems to exert a synergistic effect by improving physical performance. Even in environmental conditions that are not extreme, internal cooling strategies may have an ergogenic effect. Further studies exploring both intermittent and outdoor exercise protocols, involving elite male and female athletes and performed under not extreme environmental conditions are warranted. Systematic review registration: [https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021268197], identifier [CRD42021268197].

Ice Ingestion Maintains Cognitive Performance during a Repeated Sprint Performance in The Heat

This study investigated the effects of precooling via crushed ice ingestion on cognitive performance during repeated-sprint cycling in the heat. Nine males, non-heat acclimatised to heat (mean age: 28.2 ± 2.7 y; height: 175.7 ± 9.7 cm; body-mass: 76.9 ± 10.6 kg) completed a 30 min bout of repeated-sprint (36 × 4 s sprints, interspersed with 56 s rest-breaks) on a cycle ergometer in a climate chamber (35°C, 70% relative humidity). Crushed ice ingestion (7g·kg^-1, -0.4°C, ICE) or no cooling (CON) interventions were completed at rest, in the climate chamber, 30 min prior to exercise. Working memory was assessed via the serial seven test (S7) and the automated operation span task (OSPAN) at various time points before, during, and post-exercise. Core body temperature (T_c), forehead temperature (T_h), and thermal sensation (TS) were assessed throughout the protocol. Working memory significantly declined during exercise in CON as measured by S7 (p = 0.01) and OSPAN (p = 0.03); however, it was preserved in ICE with no change at the end of exercise in either S7 or OSPAN scores compared to baseline (p = 0.50, p = 0.09, respectively). Following precooling, T_h (-0.59°C, p < 0.001) and T_c (-0.67°C, p = 0.005) were significantly decreased in ICE compared to CON. At the end of the exercise, ICE significantly reduced T_c compared to CON (p = 0.03), but no significant differences were recorded for T_h. Further, TS was lower following precooling in ICE (p = 0.008) but not during exercise. In conclusion, ice ingestion significantly reduced T_h and T_c and facilitated maintenance of cognitive performance during repeated-sprint exercise in the heat, which may lead to better decision making.

Relationship Between Pre- and Post-exercise Body Mass Changes and Pre-exercise Urine Color in Female Athletes

Although studies use body mass changes or urine color to measure hydration status, the purpose of this study was to examine the relationship between pre-practice urine color and exercise body mass changes in female tackle football players. Twenty-six female American football players (Age: 29.9 ± 7.3 years; Height: 165.2 ± 2.6 cm; Weight: 83.8 ± 24.4 kg) volunteered. Fluid consumptions (FC) was measured during tackle football practices, while urine color (Ucol), and percent body mass loss (%BML) were taken before and after practices. Subjects were grouped by %BML: lost mass (LM), gained mass (GM), or no change (NC). A one-way ANOVA compared groups on Ucol and FC. There were differences across groups for pre-practice Ucol (P &lt; 0.01) and FC (P &lt; 0.01). GM had a higher pre-practice Ucol than LM (P &lt; 0.01) and NC (P &lt; 0.05) and consumed more fluid than LM (P &lt; 0.01) and NC (P &lt; 0.05). A stepwise linear regression examined the extent that Ucol and FC were related to %BML. When predicting BML, FC accounted for 45% of variance (P &lt; 0.01). The addition of pre-practice Ucol increased predicted variance explained (R2 change= 2.5%, P = 0032). Subjects who gained mass during practice arrived with elevated urine color (Ucol 5 ± 2), while those who lost mass arrived with pale urine color (Ucol 3 ± 2). Findings indicate those who arrived with an elevated urine color attempted to improve hydration status by consuming more fluid and gaining body mass during exercise.

The Influence of a Competitive Field Hockey Match on Cognitive Function

Despite the known positive effects of acute exercise on cognition, the effects of a competitive team sport match are unknown. In a randomized crossover design, 20 female and 17 male field hockey players (19.7 ± 1.2 years) completed a battery of cognitive tests (Visual Search, Stroop, Corsi Blocks, and Rapid Visual Information Processing) prior to, at half-time, and immediately following a competitive match (or control trial of seated rest); with effect sizes (ES) presented as raw ES from mixed effect models. Blood samples were collected prior to and following the match and control trial, and analyzed for adrenaline, noradrenaline, brain derived neurotrophic factor (BDNF), cathepsin B, and cortisol. The match improved response times for a simple perception task at full-time (ES = –14 ms; P < 0.01) and response times on the complex executive function task improved at half-time (ES = –44 ms; P < 0.01). Working memory declined at full-time on the match (ES = –0.6 blocks; P < 0.01). The change in working memory was negatively correlated with increases in cortisol (r = –0.314, P = 0.01; medium), as was the change in simple perception response time and the change in noradrenaline concentration (r = –0.284, P = 0.01; small to medium). This study is the first to highlight the effects a competitive hockey match can have on cognition. These findings have implications for performance optimization, as understanding the influence on specific cognitive domains across a match allows for the investigation into strategies to improve these aspects.

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

Hot environments can impair the complex cognitive functions that are crucial to baseball hitting and defense. This study investigated the effects of intermittent forehead and neck cooling on the hitting and reactive agility of baseball players in hot environments. Ten male collegiate baseball players played 7-inning intrasquad games in a hot environment (31.1°C - 33.4°C), completing one cooling and one control trial in a randomized crossover design. In the cooling trial, the participants placed ice-cold towels on their forehead and neck for 3 min during offensive half innings. Hitting and reactive agility tests, a go/no-go task, and the Stroop Color and Word Test were administered before and after each game. The games in the hot environment significantly increased rectal temperatures to the same level in the control (38.15°C ± 0.31°C, p < 0.001) and cooling (38.08°C ± 0.24°C, p < 0.001) trials. Intermittent cooling significantly reduced forehead and tympanic temperatures, perceived exertion, and thermal sensation during the game. Swing power significantly increased after the game, but the exit velocity of batted balls did not significantly differ in both trials. Reactive agility was significantly impaired after the game in the control trial (before: 0.367 ± 0.109 s, after: 0.491 ± 0.212 s, p = 0.008) but displayed a trend of decrease in the cooling trial (before: 0.390 ± 0.183 s, after: 0.518 ± 0.282 s, p = 0.066). The game and cooling intervention had no significant effects on the reaction time or error rate in the go/no-go task and Stroop Color and Word Test. The results showed that intermittent cooling during a baseball game in a hot environment reduces perceived exertion and thermal sensation but has no significant effect on hitting, defense performance, or cognitive function.

Modified Stroop Task Performance When Wearing Protective Clothing in the Heat: An Evaluation of the Maximum Adaptability Model

INTRODUCTION

This exploratory study investigated whether performance in a behavioural inhibition task followed the shape proposed by the Maximum Adaptability Model during progressive exertional heat stress-that is, an initial improvement in cognitive performance is followed by a plateau, and subsequent decline once body temperature continues to rise unabated.

METHODS

Seventeen adult males walked on a treadmill at 4 km•h^-1 (1% grade) for up to 120 min, in three protective clothing ensembles, across three simulated environments. The simulated environments were equivalent to wet bulb globe temperatures 21, 30 and 37°C. Cognitive function was assessed using a modified colour-word Stroop Task, with performance expressed as inverse efficiency scores in the simple (congruent) and more complex (incongruent) task conditions. The Stroop Task was completed before a trial, at termination, and every 30 min during walking, and core body temperature was continuously measured. Data were modelled using Bayesian penalised regression, with core body temperature included as a non-linear term (i.e., second degree polynomial).

RESULTS

We did not find any evidence that core body temperature had an effect on congruent or incongruent inverse efficiency scores, and no evidence that the relationship between these variables followed the shaped described by the Maximum Adaptability Model. There was, however, evidence that higher pre-exercise serum osmolality values were associated with slower congruent (β = 9.19) and incongruent (β = 8.67) inverse efficiency scores. The posterior probability that these effects were greater than zero was 0.971 and 0.952, respectively.

CONCLUSIONS

In young, fit men, performance in the behavioural inhibition task was unaffected by increases in body temperature up to 39°C and did not follow the shape proposed by the Maximum Adaptability Model. A secondary finding of the study was that pre-exercise hydration status affected performance in the inhibition task. Future studies are needed to confirm this result.

Passive heat acclimation does not modulate processing speed and executive functions during cognitive tasks performed at fixed levels of thermal strain

PURPOSE

This study evaluated if passive controlled hyperthermia heat acclimation (HA) modulates cognitive performance during passive heat stress.

METHODS

Eight healthy adults (25 ± 4 years) underwent 7 consecutive days of hot water immersion (core temperature ≥38.6°C) and a 7-day time-control period. On days 1 and 7 of HA, participants performed a digital Stroop test at baseline, when core temperature reached 38.6°C, and after 60 minutes at a core temperature ≥38.6°C to evaluate reaction time during tasks targeting processing speed (reading and counting) and executive functions (inhibition and switching). On days 1 and 7 of the time-control intervention, participants performed the Stroop test with equivalent amounts of time separating each task as for HA.

RESULTS

During day 1 of HA, reaction time was quicker during the reading (-44 ms [-71, -17], P<0.01) and counting (-39 ms [-76, -2], P=0.04) tasks when rectal temperature reached 38.6°C, but after a further 60 minutes of heat exposure, reaction time only remained quicker during the reading task (-56 ms [-83, -29], P<0.01). Changes in reaction time during heat exposure were unaffected by subsequent HA (interaction, all P≥0.09).

CONCLUSION

Seven days of HA does not modulate processing speed and executive functions during passive heat exposure. Novelty: - Whether heat acclimation (HA) to improve cognitive performance during heat exposure remains understudied. - We tested the hypothesis that HA modulates reaction time during cognitive tasks performed at matched levels of thermal strain. - Despite classical signs of HA, reaction time during heat exposure was unaffected by HA.

Carbohydrate ingestion attenuates cognitive dysfunction following long-duration exercise in the heat in humans

INTRODUCTION

To determine if electrolyte or carbohydrate supplementation vs. water would limit the magnitude of dehydration and decline in cognitive function in humans following long-duration hyperthermic-exercise.

METHODS

24 subjects performed 3 visits of 2 h walking (3mph/7% grade) in an environmental chamber (33 °C/10% relative humidity). In random order, subjects consumed water (W), electrolytes (Gatorade Zero; E), or electrolytes+carbohydrates (Gatorade; E+C). Throughout exercise (EX), subjects carried a 23 kg pack and drank ad-libitum. Pre-and post-EX, body mass (BM) and plasma osmolality (pOsm) were measured. Physiological Strain Index (PSI) and core temperature (T_C) were recorded every 15 min. Plasma glucose (GLU) was measured every 30 min. Cognitive processing (SCWT) was measured post-EX and compared to baseline (BL). A subset of 8 subjects performed a normothermic (N) protocol (21 °C/ambient humidity) to ascertain how the exercise stimulus influenced hydration status and cognition without heat.

RESULTS

There were no significant differences between fluid conditions (W, E, E+C) for BM loss (Δ2.5 ± 0.2, 2.5 ± 0.2, 2.3 ± 0.2 kg), fluid consumption (1.9 ± 0.2, 1.9 ± 0.2, 1.8 ± 0.2L), pOsm (Δ1.5 ± 2.7, 2.2 ± 2.4, 2.0 ± 1.5 mmol/L), peak-PSI (7.5 ± 0.4, 7.0 ± 0.6, 7.9 ± 0.5), and peak-T_C (38.7 ± 0.1, 38.6 ± 0.2, 38.8 ± 0.2 °C). GLU decreased significantly in W and E, whereas it increased above BL in E+C at 60, 90, and 120 min (P < 0.05). Compared to BL values (43.6 ± 26 ms), SCWT performance significantly decreased in all conditions (463 ± 93, 422 ± 83, 140 ± 52 ms, P < 0.05). Importantly, compared to W and E, the impairment in SCWT was significantly attenuated in E+C (P < 0.05). As expected, when compared to the heat-stress protocol (W, E, E+C), N resulted in lower BM loss, fluid consumption, and peak-PSI (1.1 ± 0.1 kg, 1.2 ± 0.7L, 4.8, respectively), and improved SCWT performance.

CONCLUSIONS

These data are the first to suggest that, independent of supplementation variety, cognitive processing significantly decreases immediately following long-duration exercise in the heat in healthy humans. Compared to water and fluids supplemented with only electrolytes, fluids supplemented with carbohydrates significantly blunts this decrease in cognitive function.

Proposed framework for forecasting heat-effects on motor-cognitive performance in the Summer Olympics

Heat strain impairs performance across a broad spectrum of sport disciplines. The impeding effects of hyperthermia and dehydration are often ascribed to compromised cardiovascular and muscular functioning, but expert performance also depends on appropriately tuned sensory, motor and cognitive processes. Considering that hyperthermia has implications for central nervous system (CNS) function and fatigue, it is highly relevant to analyze how heat stress forecasted for the upcoming Olympics may influence athletes. This paper proposes and demonstrates the use of a framework combining expected weather conditions with a heat strain and motor-cognitive model to analyze the impact of heat and associated factors on discipline- and scenario-specific performances during the Tokyo 2021 games. We pinpoint that hyperthermia-induced central fatigue may affect prolonged performances and analyze how hyperthermia may impair complex motor-cognitive performance, especially when accompanied by either moderate dehydration or exposure to severe solar radiation. Interestingly, several short explosive performances may benefit from faster cross-bridge contraction velocities at higher muscle temperatures in sport disciplines with little or no negative heat-effect on CNS fatigue or motor-cognitive performance. In the analyses of scenarios and Olympic sport disciplines, we consider thermal impacts on “motor-cognitive factors” such as decision-making, maximal and fine motor-activation as well as the influence on central fatigue and pacing. From this platform, we also provide perspectives on how athletes and coaches can identify risks for their event and potentially mitigate negative motor-cognitive effects for and optimize performance in the environmental settings projected.

Influence of Hot Environment on Pitching and Hitting Performance in Professional Baseball

ABSTRACT

Huang, J-H, Chiu, Y-C, and Chang, C-K. The influence of hot environment on pitching and hitting performance in professional baseball. J Strength Cond Res XX(X): 000-000, 2021-Baseball is usually played outdoors during the warmest months of the year. The long exposure to a hot environment may lead to hyperthermia and subsequent impaired cognitive function, which is crucial for hitting and pitching performance in baseball. The purpose of this study was to investigate the effect of apparent temperature on pitching and hitting performance in Chinese Professional Baseball League games in Taiwan. Each pitched and batted ball from a total of 480 regular season games in 2018 and 2019 was analyzed. Each game was categorized into one of the 4 groups on the basis of the average apparent temperature at which it was played: cold (below 21° C), warm (21-28° C), hot (28-34° C), or extremely hot (above 34° C). Differences in pitching and hitting variables were compared across the 4 groups. In the extremely hot environment, slugging percentage, isolated power, base on balls per 9 innings, home runs per 9 innings, and walks plus hits per inning were all significantly higher than those in the other 3 environments. The results suggest that offensive production was significantly increased in extremely hot environments in the Chinese Professional Baseball League. It is recommended that pitchers could adopt cooling interventions to alleviate the decline in performance in an extremely hot environment.

Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies

A rise in body core temperature and loss of body water via sweating are natural consequences of prolonged exercise in the heat. This review provides a comprehensive and integrative overview of how the human body responds to exercise under heat stress and the countermeasures that can be adopted to enhance aerobic performance under such environmental conditions. The fundamental concepts and physiological processes associated with thermoregulation and fluid balance are initially described, followed by a summary of methods to determine thermal strain and hydration status. An outline is provided on how exercise-heat stress disrupts these homeostatic processes, leading to hyperthermia, hypohydration, sodium disturbances, and in some cases exertional heat illness. The impact of heat stress on human performance is also examined, including the underlying physiological mechanisms that mediate the impairment of exercise performance. Similarly, the influence of hydration status on performance in the heat and how systemic and peripheral hemodynamic adjustments contribute to fatigue development is elucidated. This review also discusses strategies to mitigate the effects of hyperthermia and hypohydration on exercise performance in the heat by examining the benefits of heat acclimation, cooling strategies, and hyperhydration. Finally, contemporary controversies are summarized and future research directions are provided.

Does Hydration Status Influence Executive Function? A Systematic Review

BACKGROUND

Cognitive function, including executive function (EF)-related capacities (eg, working memory, inhibitory and attentional control), has been linked to adherence to healthy lifestyle behaviors. Dehydration is associated with impaired cognitive function, whereas improvements in hydration status may improve inhibitory and attentional performance. No systematic reviews have examined the effects of both dehydration and euhydration on EF.

OBJECTIVE

The objectives of this systematic review are to examine studies that have investigated the spectrum of hydration status and EF in adults, and to identify future research needs.

DESIGN

The review was conducted according to the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. The database search was initially conducted on May 12, 2019 and then updated on April 26, 2020. Databases searched included PubMed, Medline, Psyc Info, SCOPUS, Proquest, and ISI Web of Science. Data extraction included the following: method used to assess de/hydration status, study design, participant characteristics, EF tasks and domain, and results. Article quality ratings were performed on included studies using the Academy of Nutrition and Dietetics Quality Rating Checklist.

PARTICIPANTS/SETTING

Studies done with healthy or diseased adults, aged older than 18 years, in any setting, were included. Studies of individuals with disease states that impact fluid balance or require fluid restrictions as treatments were excluded.

MAIN OUTCOME MEASURE

All EF-related outcomes were included, such as working memory, inhibitory control, task switching, and attention.

RESULTS

Four thousand eight hundred thirty-three articles were screened using title/abstracts. Seventy-one full-text articles were assessed for eligibility; 33 were included (26 included investigations of dehydration; 27 included investigations of rehydration/euhydration) with 3,636 participants across all studies. Little consistency was found across outcomes. Roughly half of the available studies suggested unclear or neutral EF effects, and half suggested effects on EF domains, particularly working memory, inhibitory control, and attention. Studies including a euhydration condition were slightly more likely to demonstrate improvements to EF capacities.

CONCLUSIONS

Overall, there is a strong need for consistent methodological approaches and a greater number of long-term (ie, >3 days) studies of dehydration and euhydration and EF.

Impact of elevated core temperature on cognition in hot environments within a military context

PURPOSE

Cognition can be impaired during exercise in the heat, potentially contributing to military casualties. To our knowledge, the independent role of elevated core temperature during exercise has not been determined. The aim of the current study was to evaluate effects of elevated core temperature on cognition during physically encumbering, heated exercise, and to determine whether the perceptual cooling effects of menthol preserves cognition.

METHODS

Eight participants complete three trials in randomised order: one normothermic (CON) and two with elevated (38.5°C) core temperature, induced by prior immersion in neutral versus hot water The CON trial and one hot trial (HOT) used a water mouth-rinse following each cognitive task of the trial, (HOT) while the other used a menthol mouth-rinse (MENT). Participants walked in humid heat (33°C, 75% relative humidity) in military clothing, completing a cognitive battery of reaction time, perceptual processing, working memory, executive function, cognitive flexibility, vigilance, and declarative memory.

RESULTS

No differences in cognitive performance were observed between any conditions. Near-infrared spectroscopy showed greater oxygenated haemoglobin tissue content in HOT and MENT compared to CON (ΔO₂Hb-deO₂Hb: 2.3 ± 4.5 µM, p < .024), and lower deoxygenated haemoglobin in MENT than in CON or HOT (p = .017), suggesting higher brain metabolism during the more stressful conditions.

CONCLUSION

Moderately elevated core (38.5°C) and skin temperature does not appear to impair cognitive performance during exercise despite mildly elevated cerebral metabolism. The effects of menthol remain undetermined due to the lack of heat-mediated cognitive impairment.

Effect of continuous cooling on inhibition and attention while wearing firefighter's PPE in a hot environment

Firefighting is physically and mentally strenuous, requiring rapid, appropriate decision-making in hot environments. Intact cognitive function is imperative to firefighters' effectiveness and safety. The study purpose was to investigate the effect of hyperthermia and the effect of body cooling on sustained attention and response inhibition while wearing firefighters' personal protective ensembles after exercise in a hot environment. Twelve healthy males were recruited to participate in two randomly assigned exercise sessions (walking on a treadmill for 40 min at 40% [Formula: see text] O_2max while wearing firefighter's protective ensemble) in a hot environment: control (no cooling) and intervention (cooling). For intervention sessions, a cooling garment was worn underneath firefighter's protective ensemble and infused with 18 °C water supplied by an external water circulator. Participants performed a computerized Go/No-Go (a measure of cognitive function) test three times at baseline and post-exercise for each experimental session. Participants completed baseline testing while wearing cotton athletic clothing. The exercise continued until the core temperature reached ∼39 °C (for all subjects regardless of cooling or non-cooling experimental sessions). Following hyperthermia, participants' physiological responses were significantly increased after exercise. Subjects' reaction time was significantly reduced (improved) after experiencing thermal strain and reaching hyperthermia. The cooling method had a significant impact on suppressing the physiological load, i.e., body cooling delayed the time to reach a T_c of 39 °C (p ≤ 0.05), but not cognitive inhibition and attention (reaction time and accuracy). Unexpectedly, hyperthermia resulted in shorter reaction time following exercise (16.64 ± 5.62; p < 0.03), likely influenced by increased attention/vigilance. Hyperthermia may trigger an acute increase in alertness, causing decreased reaction time.

Per-Cooling (Using Cooling Systems during Physical Exercise) Enhances Physical and Cognitive Performances in Hot Environments. A Narrative Review

There are many important sport events that are organized in environments with a very hot ambient temperature (Summer Olympics, FIFA World Cup, Tour de France, etc.) and in hot locations (e.g., Qatar). Additionally, in the context of global warming and heat wave periods, athletes are often subjected to hot ambient temperatures. It is known that exercising in the heat induces disturbances that may provoke premature fatigue and negatively affects overall performance in both endurance and high intensity exercises. Deterioration in several cognitive functions may also occur, and individuals may be at risk for heat illnesses. To train, perform, work and recover and in a safe and effective way, cooling strategies have been proposed and have been routinely applied before, during and after exercise. However, there is a limited understanding of the influences of per-cooling on performance, and it is the subject of the present review. This work examines the influences of per-cooling of different areas of the body on performance in terms of intense short-term exercises ("anaerobic" exercises), endurance exercises ("aerobic" exercises), and cognitive functioning and provides detailed strategies that can be applied when individuals train and/or perform in high ambient temperatures.

The impact of perceived heat stress symptoms on work-related tasks and social factors: A cross-sectional survey of Australia's Monsoonal North

Heat poses a significant occupational hazard for labour-intensive workers in hot and humid environments. Therefore, this study measured the prevalence of heat-stress symptoms and impact of heat exposure on labour-intensive industries within the Monsoonal North region of Australia. A cohort of 179 workers completed a questionnaire evaluating environmental exposure, chronic (recurring) and/or severe (synonymous with heat stroke) symptoms of heat stress, and impact within work and home settings. Workers reported both chronic (79%) and severe (47%) heat stress symptoms, with increased likelihood of chronic symptoms when exposed to heat sources (OR 1.5-1.8, p = 0.002-0.023) and decreased likelihood of both chronic and severe symptoms when exposed to air-conditioning (Chronic: OR 0.5, p = <0.001, Severe: OR 0.7, p = 0.019). Negative impacts of heat exposure were reported for both work and home environments (30-60% respectively), highlighting the need for mitigation strategies to reduce occupational heat stress in the Monsoonal North.

Pre-exercise hypohydration prevalence in soccer players: A quantitative systematic review

Pre-exercise hypohydration can impair soccer performance and has been extensively studied in different soccer populations. Therefore, the aim of this systematic review was to report hypohydration prevalence, measured by blood or urine samples, in different soccer populations based on sex (males and females), performance level (professional and recreational players) and context (training sessions and games). The Pubmed, Web of Science and SPORTDiscus databases were systematically searched until November 2018. Data were pooled to compare hypohydration prevalence between the different subgroups. Following the systematic search selection process, 24 studies were included. The results indicated that overall pre-exercise hypohydration prevalence was 63.3%, 37.4% and 58.8% for urine specific gravity (USG), urine osmolality (U Osm) and urine colour, respectively. Furthermore, no study implemented blood samples to examine hypohydration prevalence in soccer players. The subgroup analyses using USG data indicated that pre-exercise hypohydration prevalence was significantly higher amongst males (66.0%; p = 0.001), professional soccer players (66.2%; p = 0.020) and before a training session (79.6%; p < 0.001). Pre-exercise hypohydration prevalence was 46.8% among female soccer players, 55.6% in recreational soccer players and 41,3% before a game. The subgroup analyses using U Osm data indicated that hypohydration prevalence was significantly higher before a training session (52.6%; p = 0.023). Based on these results, it can be concluded that hypohydration prevalence in soccer players is of major concern. Future research should explore how pre-exercise hydration status can be improved in a sustainable way.

Honey Supplementation and Exercise: A Systematic Review

Honey is a natural substance formed primarily of carbohydrates (~80%) which also contains a number of other compounds purported to confer health benefits when consumed. Due to its carbohydrate composition (low glycaemic index, mostly fructose and glucose), honey may theoretically exert positive effects when consumed before, during or after exercise. This review therefore appraised research examining the effects of honey consumption in combination with exercise in humans. Online database (PubMed, MEDLINE, SPORTDiscus) searches were performed, yielding 273 results. Following duplicate removal and application of exclusion criteria, nine articles were reviewed. Large methodological differences existed in terms of exercise stimulus, population, and the nutritional interventions examined. All nine studies reported biochemical variables, with four examining the effects of honey on exercise performance, whilst five described perceptual responses. Acute supplementation around a single exercise session appeared to elicit similar performance, perceptual, and immunological responses compared with other carbohydrate sources, although some performance benefit has been observed relative to carbohydrate-free comparators. When consumed over a number of weeks, honey may dampen immunological perturbations arising from exercise and possibly improve markers of bone formation. More well-controlled research is required to better understand the role for honey in a food-first approach to exercise nutrition.

Hand and torso pre-cooling does not enhance subsequent high-intensity cycling or cognitive performance in heat

The purpose of this study was to compare the separate and combined effects of two practical cooling methods (hand and torso) used prior to exercise on subsequent high-intensity cycling performance in heat. Ten trained male cyclists (V̇O2peak: 65.7 ± 10.7 ml.kg-1.min-1) performed four experimental trials (randomised within-subjects design) involving 30-min of pre-cooling (20-min seated; PRE-COOL, 10 min warm-up; PRE-COOL+WUP), while using a: (1) hand-cooling glove (CG); (2) cooling jacket (CJ); (3) both CG and CJ (CG+J); or (4) no-cooling (NC) control, followed by a cycling race simulation protocol (all performed in 35.0 ± 0.6°C and 56.6 ± 4.5% RH). During the 30-min of pre-cooling, no reductions in core (Tc) or mean skin temperature (Tsk) occurred; however, Tsk remained lower in the CJ and CG+J trials compared to NC and CG (p = 0.002-0.040, d= 0.55-1.01). Thermal sensation ratings also indicated that participants felt "hotter" during NC compared to all other trials during both PRE-COOL and PRE-COOL+WUP (p = 0.001-0.015, d= 1.0-2.19), plus the early stages of exercise (sets 1-2; p = 0.005-0.050, d= 0.56-1.22). Following cooling, no differences were found for absolute Tc and Tsk responses between trials over the entire exercise protocol (p > 0.05). Exercise and cognitive (working memory) performance also did not differ between trials (p = 0.843); however, cognitive performance improved over time in all trials (p < 0.001). In summary, pre-cooling (20-min seated and 10-min warm-up) in heat did not improve subsequent high-intensity cycling performance, cognitive responses and associated thermoregulatory strain (Tc and Tsk) compared to control.

Conventional and Alternative Strategies to Cope With the Subtropical Climate of Tokyo 2020: Impacts on Psychological Factors of Performance

The thermal discomfort caused by a hot or hot-wet climate can have negative effects on human performance. The 2020 Summer Olympic and Paralympic Games will take place in Tokyo’s hot and humid summer period, possibly exposing athletes to severe environmental stressors. In addition to technical, tactical, physical and nutritional preparation, Olympians and Paralympians need an optimal psychological state to turn in their best performances, especially in terms of emotional control, concentration and motivation. Yet, the tropical climate can have many negative effects on these factors. Better understanding of the negative effects of this climate and the strategies to manage them might be crucial for competitors, coaches and their teams in Japan. At the psychological level, cooling interventions before, during and/or immediately after exercise were mainly studied on perceptual responses. However, the effects of these interventions on other psychological components such as cognitive abilities or psychological states and the use of psychological techniques have been little explored, especially in hot-wet climate. Thus, this article proposes to take stock of the knowledge on the conventional and alternative strategies that help athletes to psychologically cope with the subtropical climate of Tokyo.

Effects of Dehydration and Rehydration on Cognitive Performance and Mood among Male College Students in Cangzhou, China: A Self-Controlled Trial

Water accounts for 75% of brain mass. Associations may exist between hydration and cognitive performance. The objective of this study was to investigate the effects of dehydration and rehydration on cognitive performance and mood. In this self-control trial, 12 men were recruited from a medical college in Cangzhou, China. After 12 h of overnight fasting, the participants took baseline tests at 8:00 AM on day 2. First morning urine and blood osmolality were analyzed to determine hydration state. Height, weight, and blood pressure were measured following standardized procedures. A visual analog scale for the subjective sensation of thirst was applied, and a profile of mood states questionnaire was applied. Tests were conducted for cognitive performance, including a test of digit span forward and backward, digit-symbol substitutions, dose-work, and stroop effects. Participants were required not to drink water for 36 h but were given three meals on day 3. On day 4, the same indexes were tested as a baseline test. At 8:30 AM, participants drank 1500 mL of purified water over 15 min. After a 1 h interval, the same measurements were performed. Compared with baseline test results, during the dehydration test, participants had lower scores of vigor (11.9 vs. 8.8, %, p = 0.007) and esteem-related affect (8.2 vs. 5.7, %, p = 0.006), lower total scores of digit span (14.3 vs. 13.3, %, p = 0.004), and higher error rates for dose-work (0.01 vs. 0.16, %, p = 0.005). Compared with the dehydration test scores, rehydration test scores showed that fatigue (4.3 vs. 2.1, %, p = 0.005) and total mood disturbance (TMD) (99.0 vs. 90.2, %, p = 0.008) improved, and scores of forward, backward, and total digit span increased (7.7 vs. 8.6, p = 0.014; 5.7 vs. 1.2, p = 0.019; 13.3 vs. 15.4, p = 0.001). Increases were also noted in correct number of digit symbol substitutions, reading speed, and mental work ability (70.8 vs. 75.4, p < 0.001; 339.3 vs. 486.4, n/min, p < 0.001; 356.1 vs. 450.2, p < 0.001), and reaction time decreased (30.2 vs. 28.7, s, p = 0.002). As a conclusion, dehydration had negative effects on vigor, esteem-related affect, short-term memory, and attention. Rehydration after water supplementation alleviated fatigue and improved TMD, short-term memory, attention, and reaction.

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

Effects of exercise-heat stress with and without water replacement on brain structure and visuomotor performance were examined. Thirteen healthy adults (23.6 ± 4.2 years) completed counterbalanced 150 min trials of exercise-heat stress (45°C, 15% RH) with water replacement (EHS) or without (~3% body mass loss; EHS-DEH) compared to seated rest (CON). Anatomical scans and fMRI Blood-Oxygen-Level-Dependent responses during a visuomotor pacing task were evaluated. Accuracy decreased (P < 0.05) despite water replacement during EHS (-8.2 ± 6.8% vs. CON) but further degraded with EHS-DEH (-8.3 ± 6.4% vs. EHS and -16.5 ± 10.2% vs. CON). Relative to CON, EHS elicited opposing volumetric changes (P < 0.05) in brain ventricles (-5.3 ± 1.7%) and periventricular structures (cerebellum: 1.5 ± 0.8%) compared to EHS-DEH (ventricles: 6.8 ± 3.4, cerebellum: -0.7 ± 0.7; thalamus: -2.7 ± 1.3%). Changes in plasma osmolality (EHS: -3.0 ± 2.1; EHS-DEH: 9.3 ± 2.1 mOsm/kg) were related (P < 0.05) to thalamus (r = -0.45) and cerebellum volume (r = -0.61) which, in turn, were related (P < 0.05) to lateral (r = -0.41) and fourth ventricle volume (r = -0.67) changes, respectively; but, there were no associations (P > 0.50) between structural changes and visuomotor accuracy. EHS-DEH increased neural activation (P < 0.05) within motor and visual areas versus EHS and CON. Brain structural changes are related to bidirectional plasma osmolality perturbations resulting from exercise-heat stress (with and without water replacement), but do not explain visuomotor impairments. Negative impacts of exercise-heat stress on visuomotor tasks are further exacerbated by dehydration.

Effects of heat stress and dehydration on cognitive function in elite female field hockey players

Background

It has previously been suggested that heat exposure and hypohydration have negative effects on cognitive performance, which may impact upon sporting performance. The aim of the present study was to examine the independent effects of heat stress and hypohydration on cognitive performance in elite female field hockey players.

Methods

Eight unacclimatised elite field hockey players (age: 22 ± 3 y; height: 1.68 ± 0.05 m; body mass: 63.1 ± 6.0 kg) completed a cognitive test battery before and after 50 min of field hockey specific exercise on a treadmill in four experimental trials; two in hot conditions (33.3 ± 0.1 °C), and two in moderate (16.0 ± 3.0 °C), both with and without ad libitum water intake.

Results

On the visual search test, participants were faster overall in the heat (1941 vs. 2104 ms, p = 0.001). Response times were quicker in the heat on the Sternberg paradigm (463 vs. 473 ms, p = 0.024) and accuracy was improved (by 1.9%, p = 0.004). There was no effect of hydration status on any of the markers of cognitive function.

Conclusions

Overall, the findings suggest that in elite field hockey players exposure to heat enhances response times and/or accuracy on a battery of cognitive function tests. However, hypohydration does not appear to affect cognitive performance in elite field hockey players.

Passive Heat Exposure Alters Perception and Executive Function

Findings regarding the influence of passive heat exposure on cognitive function remain equivocal due to a number of methodological issues including variation in the domains of cognition examined. In a randomized crossover design, forty-one male participants completed a battery of cognitive function tests [Visual Search, Stroop, Corsi Blocks and Rapid Visual Information Processing (RVIP) tests] prior to and following 1 h of passive rest in either hot (39.6 ± 0.4°C, 50.8 ± 2.3% Rh) or moderate (21.2 ± 1.8°C, 41.9 ± 11.4% Rh) conditions. Subjective feelings of heat exposure, arousal and feeling were assessed alongside physiological measures including core temperature, skin temperature and heart rate, at baseline and throughout the protocol. Response times were slower in the hot trial on the simple (main effect of trial, P < 0.001) and complex (main effect of trial, P < 0.001) levels of the Stroop test (Hot: 872 ± 198 ms; Moderate: 834 ± 177 ms) and the simple level of the visual search test (Hot: 354 ± 54 ms; Moderate: 331 ± 47 ms) (main effect of trial, P < 0.001). Participants demonstrated superior accuracy on the simple level of the Visual Search test in the hot trial (Hot: 98.5 ± 3.1%; Moderate: 97.4 ± 3.6%) (main effect of trial, P = 0.035). Participants also demonstrated an improvement in accuracy on the complex level of the visual search test following 1 h passive heat exposure (Pre: 96.8 ± 5.9%; Post: 98.1 ± 3.1%), whilst a decrement was seen across the trial in the moderate condition (Pre: 97.7 ± 3.5; Post: 97.0 ± 5.1%) (time^*trial interaction, P = 0.029). No differences in performance were observed on the RVIP or Corsi Blocks tests (all P > 0.05). Subjective feelings of thermal sensation and felt arousal were higher, feeling was lower in the hot trial, whilst skin temperature, core temperature and heart rate were higher (main effects of trial, all P < 0.001). The findings of the present study suggest that response times for perception and executive function tasks are worse in the heat. An improvement in accuracy on perceptual tasks may suggest a compensatory speed-accuracy trade-off effect occurring within this domain, further highlighting the task dependant nature of heat exposure on cognition.

Carbohydrates for Soccer: A Focus on Skilled Actions and Half-Time Practices

Carbohydrate consumption is synonymous with soccer performance due to the established effects on endogenous energy store preservation, and physical capacity maintenance. For performance-enhancement purposes, exogenous energy consumption (in the form of drinks, bars, gels and snacks) is recommended on match-day; specifically, before and during match-play. Akin to the demands of soccer, limited opportunities exist to consume carbohydrates outside of scheduled breaks in competition, such as at half-time. The link between cognitive function and blood glucose availability suggests that carbohydrates may influence decision-making and technical proficiency (e.g., soccer skills). However, relatively few reviews have focused on technical, as opposed to physical, performance while also addressing the practicalities associated with carbohydrate consumption when limited in-play feeding opportunities exist. Transient physiological responses associated with reductions in activity prevalent in scheduled intra-match breaks (e.g., half-time) likely have important consequences for practitioners aiming to optimize match-day performance. Accordingly, this review evaluated novel developments in soccer literature regarding (1) the ergogenic properties of carbohydrates for skill performance; and (2) novel considerations concerning exogenous energy provision during half-time. Recommendations are made to modify half-time practices in an aim to enhance subsequent performance. Viable future research opportunities exist regarding a deeper insight into carbohydrate provision on match-day.

Fluid Balance in Team Sport Athletes and the Effect of Hypohydration on Cognitive, Technical, and Physical Performance

Sweat losses in team sports can be significant due to repeated bursts of high-intensity activity, as well as the large body size of athletes, equipment and uniform requirements, and environmental heat stress often present during training and competition. In this paper we aimed to: (1) describe sweat losses and fluid balance changes reported in team sport athletes, (2) review the literature assessing the impact of hypohydration on cognitive, technical, and physical performance in sports-specific studies, (3) briefly review the potential mechanisms by which hypohydration may impact team sport performance, and (4) discuss considerations for future directions. Significant hypohydration (mean body mass loss (BML) >2%) has been reported most consistently in soccer. Although American Football, rugby, basketball, tennis, and ice hockey have reported high sweating rates, fluid balance disturbances have generally been mild (mean BML <2%), suggesting that drinking opportunities were sufficient for most athletes to offset significant fluid losses. The effect of hydration status on team sport performance has been studied mostly in soccer, basketball, cricket, and baseball, with mixed results. Hypohydration typically impaired performance at higher levels of BML (3-4%) and when the method of dehydration involved heat stress. Increased subjective ratings of fatigue and perceived exertion consistently accompanied hypohydration and could explain, in part, the performance impairments reported in some studies. More research is needed to develop valid, reliable, and sensitive sport-specific protocols and should be used in future studies to determine the effects of hypohydration and modifying factors (e.g., age, sex, athlete caliber) on team sport performance.

Effects of Fluid Ingestion on Brain-Derived Neurotrophic Factor and Cognition During Exercise in the Heat

We investigated the effects of fluid ingestion during exercise in different environments on the serum brain-derived neurotrophic factor and cognition among athletes. Ten collegiate male athletes (soccer, n = 5; rugby, n = 5) were enrolled, and they completed running tests in the following four conditions (60 min each): 1) thermoneutral temperature at 18°C (group 18); 2) high ambient temperature at 32°C without fluid ingestion (group 32); 3) high ambient temperature at 32°C with water ingestion (group 32+W); and 4) high ambient temperature at 32°C with sports drink ingestion (group 32+S). Serum brain-derived neurotrophic factor levels significantly increased in group 18 immediately after exercise when compared with those at rest and were significantly higher than those in group 32 immediately and 60 min after exercise (p < 0.05). In the Stroop Color and Word Test, significantly increased Word, Color, and Color-Word scores were observed in group 18 immediately after exercise compared to those at rest (p < 0.05). However, the Color-Word score appeared to be significantly lower in group 32 immediately after exercise compared to the other groups (p < 0.05) and at 60 min post-exercise compared to group 18 (p < 0.05). We found that the exercise performed in a thermoneutral environment improved cognitive function, but the exercise performed in a hot environment did not. The differences according to the exercise environment would be largely affected by brain-derived neurotrophic factor, and fluid ingestion regardless of the type of drink (water or sports beverage) was assumed to have contributed to the improvement in cognitive function caused by exercising in a hot environment.

Effect of Water Supplementation on Cognitive Performances and Mood among Male College Students in Cangzhou, China: Study Protocol of a Randomized Controlled Trial

Introduction: Water accounts for about 75% of brain mass. Cognitive performances and mood may be impaired by hypohydration and improved by water supplementation. Two surveys conducted in China demonstrated that a large proportion of adults and children drank less fluid than the amounts recommended by the Chinese Nutrition Society. The association between hypohydration and cognitive performance has not been reported in China. The purpose of this study is to explore the effect of water supplementation on cognitive performances and mood among male college students in Cangzhou, China. Methods and Analysis: A randomized controlled trial is designed to test the hypothesis. A total of 68 male college students aged 18–25 years will be recruited and randomly assigned into water-supplementation group (WS group, n = 34) and no water-supplementation group (NW group, n = 34) after an overnight fasting, i.e., without eating foods and drinking fluid for 12 h. The first morning urine will be collected to determine urine osmolality on the water supplementation day. Cognitive performances and mood will be performed before water supplementation by researchers with questionnaire. Subjects in the WS group will drink 400 mL purified water within 5 min, while those in NW group will not drink any fluid. One hour later, urine will be collected and urine osmolality, cognitive performances and mood will be measured again. Mixed model of repeated measures ANOVA will be used to investigate the effect of water supplementation on cognitive performances. The study would provide information about the benefit of water supplementation on cognitive performances. Ethics and Dissemination: The study protocol is reviewed and approved by the Ethical Review Committee of the Chinese Nutrition Society. Ethical approval project identification code is CNS-2015-001. Results will be published according to the CONSORT statement and will be reported in peer-reviewed journals. Trial registration: Chinese clinical trial registry. Identifier: ChiCTR-IOR-15007020. Registry name “The effect of hydration on cognitive performance”.

Nutrition and Supplementation in Soccer

Contemporary elite soccer features increased physical demands during match-play, as well as a larger number of matches per season. Now more than ever, aspects related to performance optimization are highly regarded by both players and soccer coaches. Here, nutrition takes a special role as most elite teams try to provide an adequate diet to guarantee maximum performance while ensuring a faster recovery from matches and training exertions. It is currently known that manipulation and periodization of macronutrients, as well as sound hydration practices, have the potential to interfere with training adaptation and recovery. A careful monitoring of micronutrient status is also relevant to prevent undue fatigue and immune impairment secondary to a deficiency status. Furthermore, the sensible use of evidence-based dietary supplements may also play a role in soccer performance optimization. In this sense, several nutritional recommendations have been issued. This detailed and comprehensive review addresses the most relevant and up-to-date nutritional recommendations for elite soccer players, covering from macro and micronutrients to hydration and selected supplements in different contexts (daily requirements, pre, peri and post training/match and competition).

The Effect of Fluid Intake Following Dehydration on Subsequent Athletic and Cognitive Performance: a Systematic Review and Meta-analysis

Background

The deleterious effects of dehydration on athletic and cognitive performance have been well documented. As such, dehydrated individuals are advised to consume fluid in volumes equivalent to 1.25 to 1.5 L kg⁻¹ body mass (BM) lost to restore body water content. However, individuals undertaking subsequent activity may have limited time to consume fluid. Within this context, the impact of fluid intake practices is unclear. This systematic review investigated the effect of fluid consumption following a period of dehydration on subsequent athletic and cognitive performance.

Methods

PubMed (MEDLINE), Web of Science (via Thomas Reuters) and Scopus databases were searched for articles reporting on athletic (categorized as: continuous, intermittent, resistance, sport-specific and balance exercise) or cognitive performance following dehydration of participants under control (no fluid) and intervention (fluid intake) conditions. Meta-analytic procedures determined intervention efficacy for continuous exercise performance.

Results

Sixty-four trials (n = 643 participants) derived from 42 publications were reviewed. Dehydration decreased BM by 1.3–4.2%, and fluid intake was equivalent to 0.4–1.55 L kg⁻¹ BM lost. Fluid intake significantly improved continuous exercise performance (22 trials), Hedges’ g = 0.46, 95% CI 0.32, 0.61. Improvement was greatest when exercise was performed in hotter environments and over longer durations. The volume or timing of fluid consumption did not influence the magnitude of this effect. Evidence indicating a benefit of fluid intake on intermittent (10 trials), resistance (9 trials), sport-specific (6 trials) and balance (2 trials) exercise and on cognitive performance (15 trials) was less apparent and requires further elucidation.

Conclusions

Fluid consumption following dehydration may improve continuous exercise performance under heat stress conditions, even when the body water deficit is modest and fluid intake is inadequate for complete rehydration.

Electronic supplementary material

The online version of this article (doi:10.1186/s40798-017-0079-y) contains supplementary material, which is available to authorized users.

Timing of carbohydrate ingestion did not affect inflammatory response and exercise performance during prolonged intermittent running

Background

Carbohydrate ingestion during exercise is known to attenuate exercise-induced elevation of plasma IL-6 concentration. However, the influence of timing of carbohydrate ingestion remains unclear.

Purpose

The present study investigated the influence of different timing of carbohydrate ingestion during a simulated soccer game on exercise performance, metabolic and inflammatory responses.

Methods

Seven active males performed 3 exercise trials in a randomized order. The exercise consisted of two consecutive bouts of 45 min running (4–16 km/h), separated with 15 min rest period between bouts. The subjects ingested carbohydrate gel (1.0 g/kg) immediately before the first bout of exercise (ONE), immediately before first and second bouts of exercise (0.5 g/kg for each ingestion) (TWO) or placebo immediately before exercise (PLA) Time course changes of maximal jump height, peak power output during 6-s maximal pedaling, perceived fatigue and heart rate (HR) were monitored. Blood samples were also drawn to determine blood glucose, serum insulin, free fatty acid (FFA), myoglobin (Mb), creatine kinase (CK) and plasma IL-6 concentrations.

Results

Blood glucose and serum insulin concentrations were significantly higher in the ONE trial after first bout of 45 min exercise compared with PLA trial (P < 0.05), while serum FFA concentration was significantly elevated in PLA compared with ONE and TWO trials after second bout of exercise (P < 0.05). However, changes of jump height, peak power output during 6-s maximal pedaling, perceived fatigue, HR, or indirect muscle damage (Mb, CK) and inflammatory (IL-6) markers were not significantly different among three trials (P > 0.05).

Conclusions

The timing of carbohydrate ingestion did not affect exercise performance, exercise-induced muscle damage or inflammatory response during a simulated soccer game.

Prevalence of Dehydration Before Training Sessions, Friendly and Official Matches in Elite Female Soccer Players

This study aimed to evaluate and compare the hydration states prior to different sporting events (training sessions, friendly and official matches) in elite female soccer players and relate that to the importance that the player attached to the hydration state as a determinant of sports performance. The hydration state of 17 female elite soccer players (age: 21.5 ± 3 years; body mass: 62 ± 6 kg; body height: 165 ± 9 cm) was determined by measuring their urine specific gravity (USG) prior to three different sports events: training sessions (PT), friendly (PF) and official (PO) matches. The importance that each player attached to the hydration state as a determinant of sports performance was evaluated through a simple questionnaire. An average of 47.05% of the soccer players were severely dehydrated (USG > 1.030), 33.33% were significantly dehydrated (USG > 1.020), 17.64% were mildly dehydrated (USG > 1.010) and 1.96% were euhydrated (USG < 1.010). The average USG was 1.027 ± 0.007 (PT = 1.029 ± 0.009; PF = 1.023 ± 0.010 and PO = 1.030 ± 0.006). Differences were found between urine specific gravity prior to a friendly and an official match (p = 0.03). No relationship was found between urine specific gravity and the importance each player attached to the hydration state as a determinant of sports performance. The results show that dehydration is the most prevalent hydration state of elite soccer players before training sessions, friendly and official matches. Players were most dehydrated prior to official matches, which was unlinked to the players’ perceived importance of hydration for sports performance.

Do small differences in hydration status affect mood and mental performance?

Although it has been suggested that many in the general population are dehydrated to the extent that mood and cognition are disrupted, there has been little research investigating mild levels of dehydration. When dehydration reduces body mass by more than 2%, it has been consistently reported that mood is influenced, fatigue is greater, and alertness is lower. In contrast, the effects on cognition have been less consistent. Only a few studies have looked at females and these studies made little attempt to consider hormones that influence kidney functioning. In particular, there has been virtually no attempt to look at changes in hydration status in the range that occurs in individuals with a sedentary lifestyle in a temperate climate. There is a consequent need to study individuals who have lost up to 1% of body mass due to dehydration. While 4 intervention trials have found that the cognition of children improved in response to water consumption, the effects of water consumption on cognition in older adults, another high-risk group, have been largely ignored.

The Impact of Different Environmental Conditions on Cognitive Function: A Focused Review

Cognitive function defines performance in objective tasks that require conscious mental effort. Extreme environments, namely heat, hypoxia, and cold can all alter human cognitive function due to a variety of psychological and/or biological processes. The aims of this Focused Review were to discuss; (1) the current state of knowledge on the effects of heat, hypoxic and cold stress on cognitive function, (2) the potential mechanisms underpinning these alterations, and (3) plausible interventions that may maintain cognitive function upon exposure to each of these environmental stressors. The available evidence suggests that the effects of heat, hypoxia, and cold stress on cognitive function are both task and severity dependent. Complex tasks are particularly vulnerable to extreme heat stress, whereas both simple and complex task performance appear to be vulnerable at even at moderate altitudes. Cold stress also appears to negatively impact both simple and complex task performance, however, the research in this area is sparse in comparison to heat and hypoxia. In summary, this focused review provides updated knowledge regarding the effects of extreme environmental stressors on cognitive function and their biological underpinnings. Tyrosine supplementation may help individuals maintain cognitive function in very hot, hypoxic, and/or cold conditions. However, more research is needed to clarify these and other postulated interventions.

Circadian Phenotype Composition is a Major Predictor of Diurnal Physical Performance in Teams

Team performance is a complex phenomenon involving numerous influencing factors including physiology, psychology, and management. Biological rhythms and the impact of circadian phenotype have not been studied for their contribution to this array of factors so far despite our knowledge of the circadian regulation of key physiological processes involved in physical and mental performance. This study involved 216 individuals from 12 different teams who were categorized into circadian phenotypes using the novel RBUB chronometric test. The composition of circadian phenotypes within each team was used to model predicted daily team performance profiles based on physical performance tests. Our results show that the composition of circadian phenotypes within teams is variable and unpredictable. Predicted physical peak performance ranged from 1:52 to 8:59 p.m. with performance levels fluctuating by up to 14.88% over the course of the day. The major predictor for peak performance time in the course of a day in a team is the occurrence of late circadian phenotypes. We conclude that circadian phenotype is a performance indicator in teams that allows new insight and a better understanding of team performance variation in the course of a day as often observed in different groupings of individuals.

Effects of Hypohydration on Repeated 40-yd Sprint Performance

This study examined the effects of hypohydration on repeated 40-yd sprint performance. Anaerobically fit current and former Division II male athletes (n = 12) completed 2 bouts of 10 × 40-yd sprints followed by an agility test, dehydrated (∼3% body weight [DT]), or hydrated trial (HT). Statistical analysis of group means indicated that hypohydration had little effect on sprint times for either the first (DT= 5.38 ± 0.37; HT = 5.35 ± 0.34) or second (DT = 5.47 ± 0.39; HT = 5.42 ± 0.39) bout of 10 sprints with only sprint number 2, 5, and 6 of bout 2 reaching statistical significance. However, when individual sprint performance was considered, a greater effect was seen. In all, 83% (10 of 12) of subjects experienced a meaningful change (≥0.1 seconds) (positive or negative) in mean sprint time (DT vs. HT) for one or more bout of 10 sprints. Ratings of perceived exertion was significantly higher (∼1 unit on a 10 point scale) for DT in all sprints during bout 1 and the first 2 sprints of bout 2. These results indicate that the effect of hypohydration on repeated sprint performance varies among individuals. Some improved performance with hypohydration, while others experienced detrimental effects. Hypohydration also resulted in a particularly notable negative impact on perceptual measures of exertion even when performance was similar.

Acute Effects of Carbohydrate Supplementation on Intermittent Sports Performance

Intermittent sports (e.g., team sports) are diverse in their rules and regulations but similar in the pattern of play; that is, intermittent high-intensity movements and the execution of sport-specific skills over a prolonged period of time (~1–2 h). Performance during intermittent sports is dependent upon a combination of anaerobic and aerobic energy systems, both of which rely on muscle glycogen and/or blood glucose as an important substrate for energy production. The aims of this paper are to review: (1) potential biological mechanisms by which carbohydrate may impact intermittent sport performance; (2) the acute effects of carbohydrate ingestion on intermittent sport performance, including intermittent high-intensity exercise capacity, sprinting, jumping, skill, change of direction speed, and cognition; and (3) what recommendations can be derived for carbohydrate intake before/during exercise in intermittent sports based on the available evidence. The most researched intermittent sport is soccer but some sport-specific studies have also been conducted in other sports (e.g., rugby, field hockey, basketball, American football, and racquet sports). Carbohydrate ingestion before/during exercise has been shown in most studies to enhance intermittent high-intensity exercise capacity. However, studies have shown mixed results with regards to the acute effects of carbohydrate intake on sprinting, jumping, skill, change of direction speed, and cognition. In most of these studies the amount of carbohydrate consumed was ~30–60 g/h in the form of a 6%–7% carbohydrate solution comprised of sucrose, glucose, and/or maltodextrin. The magnitude of the impact that carbohydrate ingestion has on intermittent sport performance is likely dependent on the carbohydrate status of the individual; that is, carbohydrate ingestion has the greatest impact on performance under circumstances eliciting fatigue and/or hypoglycemia. Accordingly, carbohydrate ingestion before and during a game seems to have the greatest impact on intermittent sports performance towards the end of the game.

Repeat work bouts increase thermal strain for Australian firefighters working in the heat

BACKGROUND

Firefighters regularly re-enter fire scenes during long duration emergency events with limited rest between work bouts. It is unclear whether this practice is impacting on the safety of firefighters.

OBJECTIVES

To evaluate the effects of multiple work bouts on firefighter physiology, strength, and cognitive performance when working in the heat.

METHODS

Seventy-seven urban firefighters completed two 20-minute simulated search and rescue tasks in a heat chamber (105 ± 5°C), separated by a 10-minute passive recovery. Core and skin temperature, rate of perceived exertion (RPE), thermal sensation (TS), grip strength, and cognitive changes between simulations were evaluated.

RESULTS

Significant increases in core temperature and perceptual responses along with declines in strength were observed following the second simulation. No differences for other measures were observed.

CONCLUSIONS

A significant increase in thermal strain was observed when firefighters re-entered a hot working environment. We recommend that longer recovery periods or active cooling methods be employed prior to re-entry.

Maintaining hydration with a carbohydrate–electrolyte solution improves performance, thermoregulation, and fatigue during an ice hockey scrimmage

Research in “stop-and-go” sports has demonstrated that carbohydrate ingestion improves performance and fatigue, and that dehydration of ∼1.5%–2% body mass (BM) loss results in decreased performance, increased fatigue, and increased core temperature. The purpose of this investigation was to assess the physiological, performance, and fatigue-related effects of maintaining hydration with a carbohydrate–electrolyte solution (CES) versus dehydrating by ∼2% BM (no fluid; NF) during a 70-min ice hockey scrimmage. Skilled male hockey players (n = 14; age, 21.3 ± 0.2 years; BM, 80.1 ± 2.5 kg; height, 182.0 ± 1.2 cm) volunteered for the study. Subjects lost 1.94% ± 0.1% BM in NF, and 0.12% ± 0.1% BM in CES. Core temperature (Tc) throughout the scrimmage (10–50 min) and peak Tc (CES: 38.69 ± 0.10 vs. NF: 38.92 ± 0.11 °C; p < 0.05) were significantly reduced in CES compared with NF. Players in CES had increased mean skating speed and time at high effort between 30–50 min of the scrimmage. They also committed fewer puck turnovers and completed a higher percentage of passes in the last 20 min of play compared with NF. Postscrimmage shuttle skating performance was improved in CES versus NF and fatigue was lower following the CES trial. The results indicated that ingesting a CES to maintain BM throughout a 70-min hockey scrimmage resulted in improved hockey performance and thermoregulation, and decreased fatigue as compared with drinking no fluid and dehydrating by ∼2%.

Are we being drowned in hydration advice? Thirsty for more?

Hydration pertains simplistically to body water volume. Functionally, however, hydration is one aspect of fluid regulation that is far more complex, as it involves the homeostatic regulation of total body fluid volume, composition and distribution. Deliberate or pathological alteration of these regulated factors can be disabling or fatal, whereas they are impacted by exercise and by all environmental stressors (e.g. heat, immersion, gravity) both acutely and chronically. For example, dehydration during exercising and environmental heat stress reduces water volume more than electrolyte content, causing hyperosmotic hypohydration. If exercise continues for many hours with access to food and water, composition returns to normal but extracellular volume increases well above baseline (if exercising upright and at low altitude). Repeating bouts of exercise or heat stress does likewise. Dehydration due to physical activity or environmental heat is a routine fluid-regulatory stress. How to gauge such dehydration and - more importantly-what to do about it, are contested heavily within sports medicine and nutrition. Drinking to limit changes in body mass is commonly advocated (to maintain ≤2% reduction), rather than relying on behavioural cues (mainly thirst) because the latter has been deemed too insensitive. This review, as part of the series on moving in extreme environments, critiques the validity, problems and merits of externally versus autonomously controlled fluid-regulatory behaviours, both acutely and chronically. Our contention is that externally advocated hydration policies (especially based on change in body mass with exercise in healthy individuals) have limited merit and are extrapolated and imposed too widely upon society, at the expense of autonomy. More research is warranted to examine whether ad libitum versus avid drinking is beneficial, detrimental or neither in: acute settings; adapting for obligatory dehydration (e.g. elite endurance competition in the heat), and; development of chronic diseases that are associated with an extreme lack of environmental stress.

Cold-water immersion and iced-slush ingestion are effective at cooling firefighters following a simulated search and rescue task in a hot environment

Firefighters are exposed to hot environments, which results in elevated core temperatures. Rapidly reducing core temperatures will likely increase safety as firefighters are redeployed to subsequent operational tasks. This study investigated the effectiveness of cold-water immersion (CWI) and iced-slush ingestion (SLUSH) to cool firefighters post-incident. Seventy-four Australian firefighters (mean ± SD age: 38.9 ± 9.0 years) undertook a simulated search and rescue task in a heat chamber (105 ± 5 °C). Testing involved two 20-min work cycles separated by a 10-min rest period. Ambient temperature during recovery periods was 19.3 ± 2.7 °C. Participants were randomly assigned one of three 15-min cooling protocols: (i) CWI, 15 °C to umbilicus; (ii) SLUSH, 7 g·kg−1 body weight; or (iii) seated rest (CONT). Core temperature and strength were measured pre- and postsimulation and directly after cooling. Mean temperatures for all groups reached 38.9 ± 0.9 °C at the conclusion of the second work task. Both CWI and SLUSH delivered cooling rates in excess of CONT (0.093 and 0.092 compared with 0.058 °C·min−1) and reduced temperatures to baseline measurements within the 15-min cooling period. Grip strength was not negatively impacted by either SLUSH or CONT. CWI and SLUSH provide evidence-based alternatives to passive recovery and forearm immersion protocols currently adopted by many fire services. To maximise the likelihood of adoption, we recommend SLUSH ingestion as a practical and effective cooling strategy for post-incident cooling of firefighters in temperate regions.

Carbohydrate ingestion before and during soccer match play and blood glucose and lactate concentrations

CONTEXT

The ingestion of carbohydrate (CHO) before and during exercise and at halftime is commonly recommended to soccer players for maintaining blood glucose concentrations throughout match play. However, an exercise-induced rebound glycemic response has been observed in the early stages of the second half of simulated soccer-specific exercise when CHO-electrolyte beverages were consumed regularly. Therefore, the metabolic effects of CHO beverage consumption throughout soccer match play remain unclear.

OBJECTIVE

To investigate the blood glucose and blood lactate responses to CHOs ingested before and during soccer match play.

DESIGN

Crossover study.

SETTING

Applied research study.

PATIENTS OR OTHER PARTICIPANTS

Ten male outfield academy soccer players (age = 15.6 ± 0.2 years, height = 1.74 ± 0.02 m, mass = 65.3 ± 1.9 kg, estimated maximal oxygen consumption = 58.4 ± 0.8 mL·kg(-1)·min(-1)).

INTERVENTION(S)

Players received a 6% CHO-electrolyte solution or an electrolyte (placebo) solution 2 hours before kickoff, before each half (within 10 minutes), and every 15 minutes throughout exercise. Blood samples were obtained at rest, every 15 minutes during the match (first half: 0-15, 15-30, and 30-45 minutes; second half: 45-60, 60-75, and 75-90 minutes) and 10 minutes into the halftime break.

MAIN OUTCOME MEASURE(S)

Metabolic responses (blood glucose and blood lactate concentrations) and markers of exercise intensity (heart rate) were recorded.

RESULTS

Supplementation influenced the blood glucose response to exercise (time × treatment interaction effect: P ≤ .05), such that glucose concentrations were higher at 30 to 45 minutes in the CHO than in the placebo condition. However, in the second half, blood glucose concentrations were similar between conditions because of transient reductions from peak values occurring in both trials at halftime. Blood lactate concentrations were elevated above those at rest in the first 15 minutes of exercise (time-of-sample effect: P < .001) and remained elevated throughout exercise. Supplementation did not influence the pattern of response (time × treatment interaction effect: P = .49).

CONCLUSIONS

Ingestion of a 6% CHO-electrolyte beverage before and during soccer match play did not benefit blood glucose concentrations throughout the second half of exercise.

Exposure to hot and cold environmental conditions does not affect the decision making ability of soccer referees following an intermittent sprint protocol

Soccer referees enforce the laws of the game and the decisions they make can directly affect match results. Fixtures within European competitions take place in climatic conditions that are often challenging (e.g., Moscow ~ −5°C, Madrid ~30°C). Effects of these temperatures on player performance are well-documented; however, little is known how this environmental stress may impair cognitive performance of soccer referees and if so, whether exercise exasperates this. The present study aims to investigate the effect of cold [COLD; −5°C, 40% relative humidity (RH)], hot (HOT; 30°C, 40% RH) and temperate (CONT; 18°C, 40% RH) conditions on decision making during soccer specific exercise. On separate occasions within each condition, 13 physically active males; either semi-professional referees or semi-professional soccer players completed three 90 min intermittent treadmill protocols that simulated match play, interspersed with 4 computer delivered cognitive tests to measure vigilance and dual task capacity. Core and skin temperature, heart rate, rating of perceived exertion (RPE) and thermal sensation (TS) were recorded throughout the protocol. There was no significant difference between conditions for decision making in either the dual task (interaction effects: FALSE p = 0.46; MISSED p = 0.72; TRACKING p = 0.22) or vigilance assessments (interaction effects: FALSE p = 0.31; HIT p = 0.15; MISSED p = 0.17) despite significant differences in measured physiological variables (skin temperature: HOT vs. CONT 95% CI = 2.6 to 3.9, p < 0.001; HOT vs. COLD 95% CI = 6.6 to 9.0, p < 0.001; CONT vs. COLD 95% CI = 3.4 to 5.7, p < 0.01). It is hypothesized that the lack of difference observed in decision making ability between conditions was due to the exercise protocol used, as it may not have elicited an appropriate and valid soccer specific internal load to alter cognitive functioning.