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This article describes the development and validation of accurate whole body sweat rate prediction equations for individuals performing indoor cycle ergometer and treadmill exercise, where power output can be measured or derived from simple inputs. For cycle ergometry, 112 trials (67 participants) were used for model development and another 56 trials (42 participants) for model validation. For treadmill exercise, 171 trials (67 participants) were used for model development and another 95 trials (63 participants) for model validation. Trials were conducted over a range of dry-bulb temperature (20°C to 40°C), relative humidity (14% to 60%), and exercise intensity (∼40% to 85% of peak aerobic power) conditions, which were matched between model development and model validation. Whole body sweat rates were measured, and proprietary prediction models were developed (accounting for all relevant biophysical factors) and then validated. For model validation, mean absolute error for predicted sweating rate was 0.01 and 0.02 L·h -1 for cycle and treadmill trials, respectively. The 95% confidence intervals were modest for cycle ergometer (+0.25 and -0.22 L·h -1 ) and treadmill exercise (+0.33 and -0.29 L·h -1 ). The accounted for variance between predicted and measured values was 92% and 78% for cycle and treadmill exercise, respectively. Bland-Altman analysis indicated that zero and one predicted value exceeded the a priori acceptable level of agreement (equivalent to ±2% of total body mass in 3 h) for cycle and treadmill exercise, respectively. There were fewer trials with female subjects, but their values did not differ from those expected for males. This is the foremost study to develop and validate whole body sweat rate prediction equations for indoor treadmill and cycle ergometer exercise of moderate to high intensity. These prediction equations are publicly available for use (https://sweatratecalculator.com). NEW & NOTEWORTHY This study presents the development of new proprietary whole body sweat rate prediction models for people exercising indoors on a cycle ergometer or treadmill using simple input parameters and delivered through a publicly available online calculator: https://sweatratecalculator.com. In an independent validation group, the predictive models for both indoor cycling and treadmill exercise were accurate across moderate to high exercise intensities in temperate to hot conditions. These equations will enable individualized hydration management during physical training and exercise physiology experiments.

Objective: To evaluate the efficacy of the Fédération Internationale de Football Association (FIFA) cooling break policy against alternative cooling configurations in attenuating thermal strain during simulated football in the heat., Methods: 12 males (age: 27±6 years, V̇O 2peak : 61±7 mL/kg/min) completed five 90 min intermittent treadmill football match simulations in 40°C and 41% relative humidity (32°C wet-bulb globe temperature) with different cooling configurations: regular match without cooling breaks (REG), 3 min breaks without cooling (BRK no-cool ), 3 min breaks with cooling (BRK cool : current FIFA policy; chilled fluid ingestion and ice towel across neck and shoulders), 5 min extended half-time without cooling breaks (ExtHT only ) and 3 min cooling breaks with 5 min ExtHT (ExtHT cool ). Rectal temperature (T re ), heart rate, whole-body sweat rate (WBSR) and rating of perceived exertion (RPE) were recorded. Data are presented as mean (95% CIs)., Results: Final T re was lower in BRK no-cool (0.20°C (0.01, 0.39), p=0.038), BRK cool (0.39°C (0.21, 0.57), p<0.001) and ExtHT cool (0.40°C (0.22, 0.58), p<0.001) than REG (39.1°C (38.8, 39.3)). Mean T re was lower in ExtHT cool (38.2°C (38.0, 38.4)) than BRK cool (38.3°C (38.1, 38.5), p=0.018), BRK no-cool and ExtHT only (38.4°C (38.2, 38.6), p<0.001) and REG (38.5°C (38.3, 38.7), p<0.001). Mean heart rate was lower during BRK cool (6 beats/min (4, 7), p<0.001) and ExtHT cool (7 beats/min (6, 8), p<0.001) compared with REG. WBSR was comparable across trials (p ≥ 0.07) and RPE was attenuated during BRK cool (0.4 (0.1, 0.7), p=0.004) and ExtHT cool (0.5 (0.2, 0.7), p=0.002), compared with REG., Conclusion: BRK cool and ExtHT cool attenuated thermal, cardiovascular and perceptual strain during a simulated football match in the heat. Additional strategies may be required in field settings or under harsher conditions., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Objectives: To assess health status and heat preparation of cyclists at the 2019 Tour Down Under and determine the alignment of heat mitigation strategies with current recommendations., Design: Cohort study., Methods: Twenty-three (17 % participation rate) male World Tour cyclists from five teams and 10 countries completed a pre-competition questionnaire evaluating exertional heat illness (EHI) history, pre-race health status, and heat mitigation and recovery strategies use. Associations between arrival days pre-competition, years as professional, nationality, team, history of EHI symptoms and diagnosis on heat mitigation and recovery strategy utilisation were assessed., Results: 65 % of cyclists reported previously experiencing one or more EHI symptom (cramping: 48 %) and 22 % a diagnosis of heat stroke. In the 10 days preceding the race, 26 % experienced one or more illness symptoms. 65 % trained in the heat (acclimatisation 8-25 days; acclimation: 3-7 days), which was associated with team (P = 0.047, ϕ c  = 0.61), nationality (P = 0.009, ϕ c  = 0.86) and EHI symptoms history (P = 0.058, ϕ = 0.43). All cyclists had a hydration plan, with links to team (0.5-1.0 L·h -1 , P = 0.043, ϕ c  = 0.68) and EHI symptom history (1.0-1.5 L·h -1 , P = 0.048, ϕ = 0.476). Most had pre-cooling (87 %) and mid-cooling (83 %) strategies, most commonly cold beverages (75 %) and neck collars (78 %), respectively. All cyclists planned on using at least one recovery strategy (massage: 87 %)., Conclusions: Our data indicate good alignment with current recommendations for competing in the heat, particularly for hydration, cooling and recovery strategies. Whilst the proportion of cyclists engaging in heat acclimation/acclimatisation is encouraging, greater awareness on adapting and implementing heat training is required., Competing Interests: Declaration of interest statement None., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

This review examined the effect of acute heat mitigation strategies on physiological strain and exercise performance in females exercising in the heat. Three databases were searched for original research with an acute heat mitigation (intervention) and control strategy in active females and reporting core temperature, heart rate and/or aerobic exercise performance/capacity with ≥ 24°C wet bulb globe temperature. Hedges' g effect sizes were calculated to evaluate outcomes. Thirteen studies ( n  = 118) were included. Most studies that applied an acute heat mitigation strategy to females did not reduce thermal (9/10) or cardiovascular (6/6) strain or improve exercise performance/capacity (8/10). The most effective strategies for attenuating thermal strain were pre-cooling with ice-slurry (effect size = -2.2 [95% CI, -3.2, -1.1]) and ice-vests (-1.9 [-2.7, -1.1]), and pre- and per-cooling with an ice-vest (-1.8 [-2.9, -0.7]). Only pre-cooling with an ice-vest improved running performance (-1.8 [-2.9, -0.7]; ~0.43 min) whilst sodium hyperhydration improved cycling capacity at 70% V O 2peak (0.8 [0.0, 1.6]; ~20.1 min). There is currently limited research on acute heat mitigation strategies in females, so the evidence for the efficacy is scarce. Some studies show beneficial effects with ice-slurry, ice-vests and sodium hyperhydration, which can guide future research to support female exercise performance in the heat.

Purpose: Post-exercise passive heating has been reported to augment adaptations associated with endurance training. The current study evaluated the effect of a 4-week remotely administered, post-exercise passive leg heating protocol, using an electrically heated layering ensemble, on determinants of endurance performance., Methods: Thirty recreationally trained participants were randomly allocated to either a post-exercise passive leg heating (PAH, n = 16) or unsupervised training only control group (CON, n = 14). The PAH group wore the passive heating ensemble for 90-120 min/day, completing a total of 20 (16 post-exercise and 4 stand-alone leg heating) sessions across 4 weeks. Whole-body (peak oxygen uptake, gas exchange threshold, gross efficiency and pulmonary oxygen uptake kinetics), single-leg exercise (critical torque and NIRS-derived muscle oxygenation), resting vascular characteristics (flow-mediated dilation) and angiogenic blood measures (nitrate, vascular endothelial growth factor and hypoxia inducible factor 1-α) were recorded to characterize the endurance phenotype. All measures were assessed before (PRE), at 2 weeks (MID) and after (POST) the intervention., Results: There was no effect of the intervention on test of whole-body endurance capacity, vascular function or blood markers (p > 0.05). However, oxygen kinetics were adversely affected by PAH, denoted by a slowing of the phase II time constant; τ (p = 0.02). Furthermore, critical torque-deoxygenation ratio was improved in CON relative to PAH (p = 0.03)., Conclusion: We have demonstrated that PAH had no ergogenic benefit but instead elicited some unfavourable effects on sub-maximal exercise characteristics in recreationally trained individuals., (© 2024. The Author(s).)

Competing Interests: Declaration of interest statement No conflicts of interest.

Purpose: Accurately measuring sweat sodium concentration ([Na + ]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na + ]. This study aimed to assess the validity and reliability of the MX3 hydration testing system., Methods: Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected from three measurement sites using absorbent patches. The samples were then analysed for sweat [Na + ] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample., Results: The mean difference between measurements was 0.1 mmoL·L -1 (95% limits of agreement (LoA): - 9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L -1 . When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of - 1.7 mmoL·L -1 (95% LoA: - 0.25 X ¯ , 0.25 X ¯ ) and the CV was 9.8%., Conclusion: The MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity., (© 2024. The Author(s).)

The purpose of this study was to investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastrointestinal temperature (ΔT gi ) and whole body sweat rate (WBSR) of children exercising under uncompensable heat stress. Seventeen boys (means ± SD; 13.7 ± 1.3 yr) and 18 girls (13.7 ± 1.4 yr) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg -1 ) in 40°C and 30% relative humidity. Sex and peak oxygen consumption (V̇o 2peak ) were entered into a Bayesian hierarchical general additive model (HGAM) for T gi . Sex, V̇o 2peak , and the evaporative requirement for heat balance (E req ) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M and 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for T gi and WBSR, respectively. Conditional on sex-specific mean V̇o 2peak , ΔT gi was 1.00°C [90% credible intervals (Crl): 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇o 2peak were accounted for, the difference in ΔT gi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h -1 [-0.02, 0.07], when isolated from differences in E req . The difference in ΔT gi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Biological sex did not independently influence the ΔT gi and WBSR of children exercising under uncompensable heat stress. NEW & NOTEWORTHY Limited studies have investigated the thermoregulatory responses of boys and girls exercising under uncompensable heat stress. Boys and girls often differ in physiological characteristics other than biological sex, such as aerobic fitness and body fat percentage, which may confound interpretations. We investigated the influence of biological sex on exercise thermoregulation in children, independent of differences in aerobic fitness and body fatness.

Our aim was to develop and validate separate whole body sweat rate prediction equations for moderate to high-intensity outdoor cycling and running, using simple measured or estimated activity and environmental inputs. Across two collection sites in Australia, 182 outdoor running trials and 158 outdoor cycling trials were completed at a wet-bulb globe temperature ranging from ∼15°C to ∼29°C, with ∼60-min whole body sweat rates measured in each trial. Data were randomly separated into model development (running: 120; cycling: 100 trials) and validation groups (running: 62; cycling: 58 trials), enabling proprietary prediction models to be developed and then validated. Running and cycling models were also developed and tested when locally measured environmental conditions were substituted with participants' subjective ratings for black globe temperature, wind speed, and humidity. The mean absolute error for predicted sweating rate was 0.03 and 0.02 L·h -1 for running and cycling models, respectively. The 95% confidence intervals for running (+0.44 and -0.38 L·h -1 ) and cycling (+0.45 and -0.42 L·h -1 ) were within acceptable limits for an equivalent change in total body mass over 3 h of ±2%. The individual variance in observed sweating described by the predictive models was 77% and 60% for running and cycling, respectively. Substituting measured environmental variables with subjective assessments of climatic characteristics reduced the variation in observed sweating described by the running model by up to ∼25%, but only by ∼2% for the cycling model. These prediction models are publicly accessible (https://sweatratecalculator.com) and can guide individualized hydration management in advance of outdoor running and cycling. NEW & NOTEWORTHY We report the development and validation of new proprietary whole body sweat rate prediction models for outdoor running and outdoor cycling using simple activity and environmental inputs. Separate sweat rate models were also developed and tested for situations where all four environmental parameters are not available, and some must be subsequently estimated by the user via a simple rating scale. All models are freely accessible through an online calculator: https://sweatratecalculator.com. These models, via the online calculator, will enable individualized hydration management for training or recreational cycling or running in an outdoor environment.

This study aimed to investigate seasonal heat acclimatization in active adolescents following summer. Fifteen (5 females) active adolescents (14.6 ± 1.0 y) completed a 45-min heat response test (HRT) walking at 60% V ˙ O 2peak in 40°C and 30% relative humidity before and after summer (i.e. November 2022 and March 2023). During the HRT, gastro-intestinal temperature (T gi ), skin temperature (T sk ), heart rate, local sweat rate (LSR) and whole-body sweat loss (WBSL) were recorded. Carbon monoxide rebreathing and dual-energy X-ray absorptiometry scans determined resting hematological measures and body composition. Participants completed physical activity (PA) diaries and wore an accelerometer for two one-week periods (pre- and post-summer). Daytime wet-bulb globe temperature (WBGT) was calculated for each summer day. Data are presented as posterior mean and 90% credible intervals. Participants reported 7 ± 4 h·wk -1 of outdoor PA, and daytime WBGT was 21.2 ± 4.6°C. Following summer, resting T gi and heart rate were reduced by 0.2°C [-0.3, -0.1; probability of direction = 99%] and 7 beats·min -1 [-10, -3; 100%], respectively. During the HRT, there was an earlier onset of sweating (-0.2°C [-0.3, -0.0; 98%]), an attenuated rise of T gi (0.2°C [-0.5, 0.0; 92%]) and mean T sk changed by -0.2°C [-0.5, 0.1; 86%]. There was minimal evidence for heat adaptations in LSR or WBSL, hematological parameters or perceptual measures. This is the first study to demonstrate seasonal heat adaptations in active adolescents. Reductions in resting T gi and exercising T sk and a lower T gi at the onset of sweating were associated with a smaller rise in T gi during the HRT following summer., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2024 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

Purpose: This study aimed to investigate the associations of biological sex and aerobic fitness (i.e., V̇O 2peak ) on the change in gastrointestinal temperature (∆ Tgi ) and whole-body sweat rate (WBSR) of children exercising in warm conditions., Methods: Thirty-eight children (17 boys, mean ± SD = 13.7 ± 1.2 yr; 21 girls, 13.6 ± 1.8 yr) walked for 45 min at a fixed rate of metabolic heat production (8 W·kg -1 ) in 30°C and 40% relative humidity. Biological sex and relative V̇O 2peak were entered as predictors into a Bayesian hierarchical generalized additive model for Tgi . For a subsample of 13 girls with measured body composition, body fat percent was entered into a separate hierarchical generalized additive model for Tgi . Sex, V̇O 2peak , and the evaporative requirement for heat balance ( Ereq ) were entered into a Bayesian hierarchical linear regression for WBSR., Results: The mean ∆ Tgi for boys was 0.71°C (90% credible interval = 0.60-0.82) and for girls 0.78°C (0.68-0.88). A predicted 20 mL·kg -1 ·min -1 higher V̇O 2peak resulted in a 0.19°C (-0.03 to 0.43) and 0.24°C (0.07-0.40) lower ∆ Tgi in boys and girls, respectively. A predicted ~13% lower body fat in the subsample of girls resulted in a 0.15°C (-0.12 to 0.45) lower ∆ Tgi . When Ereq was standardized to the grand mean, the difference in WBSR between boys and girls was -0.00 L·h -1 (-0.06 to 0.06), and a 20-mL·kg -1 ·min -1 higher predicted V̇O 2peak resulted in a mean difference in WBSR of -0.07 L·h -1 (-0.15 to 0.00)., Conclusions: Biological sex did not independently influence ∆ Tgi and WBSR in children. However, a higher predicted V̇O 2peak resulted in a lower ∆ Tgi of children, which was not associated with a greater WBSR, but may be related to differences in body fat percent between high and low fitness individuals., (Copyright © 2023 by the American College of Sports Medicine.)

Background: Determining the incidence and prevalence of injury and illness in short-course triathletes would improve understanding of their etiologies and therefore assist in the development and implementation of prevention strategies. This study synthesizes the existing evidence on the incidence and prevalence of injury and illness and summarizes reported injury or illness etiology and risk factors affecting short-course triathletes., Methods: This review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies reporting health problems (injury and illness) in triathletes (all sexes, ages, and experience levels) training and/or competing in short-course distances were included. Six electronic databases (Cochrane Central Register of Controlled Trials, MEDLINE, Embase, APA PsychINFO, Web of Science Core Collection, and SPORTDiscus) were searched. Risk of bias was independently assessed by 2 reviewers using the Newcastle-Ottawa Quality Assessment Scale. Two authors independently completed data extraction., Results: The search yielded 7998 studies, with 42 studies eligible for inclusion. Twenty-three studies investigated injuries, 24 studies investigated illnesses, and 5 studies investigated both injuries and illnesses. The injury incidence rate ranged 15.7-24.3 per 1000 athlete exposures, and the illness incidence rate ranged 1.8-13.1 per 1000 athlete days. Injury and illness prevalence ranged between 2%-15% and 6%-84%, respectively. Most injuries reported occurred during running (45%-92%), and the most frequently reported illnesses affected the gastrointestinal (7%-70%), cardiovascular (14%-59%), and respiratory systems (5%-60%)., Conclusion: The most frequently reported health problems in short-course triathletes were: overuse and lower limb injuries associated with running; gastrointestinal illnesses and altered cardiac function, primarily attributable to environmental factors; and respiratory illness mostly caused by infection., (Copyright © 2023. Production and hosting by Elsevier B.V.)

Background: Athletes and military personnel are often expected to compete and work in hot and/or humid environments, where decrements in performance and an increased risk of exertional heat illness are prevalent. A physiological strategy for reducing the adverse effects of heat stress is to acclimatise to the heat., Objective: The aim of this systematic review was to quantify the effects of relocating to a hotter climate to undergo heat acclimatisation in athletes and military personnel., Eligibility Criteria: Studies investigating the effects of heat acclimatisation in non-acclimatised athletes and military personnel via relocation to a hot climate for < 6 weeks were included., Data Sources: MEDLINE, SPORTDiscus, CINAHL Plus with Full Text and Scopus were searched from inception to June 2022., Risk of Bias: A modified version of the McMaster critical review form was utilised independently by two authors to assess the risk of bias., Data Synthesis: A Bayesian multi-level meta-analysis was conducted on five outcome measures, including resting core temperature and heart rate, the change in core temperature and heart rate during a heat response test and sweat rate. Wet-bulb globe temperature (WBGT), daily training duration and protocol length were used as predictor variables. Along with posterior means and 90% credible intervals (CrI), the probability of direction (Pd) was calculated., Results: Eighteen articles from twelve independent studies were included. Fourteen articles (nine studies) provided data for the meta-analyses. Whilst accounting for WBGT, daily training duration and protocol length, population estimates indicated a reduction in resting core temperature and heart rate of - 0.19 °C [90% CrI: - 0.41 to 0.05, Pd = 91%] and - 6 beats·min -1 [90% CrI: - 16 to 5, Pd = 83%], respectively. Furthermore, the rise in core temperature and heart rate during a heat response test were attenuated by - 0.24 °C [90% CrI: - 0.67 to 0.20, Pd = 85%] and - 7 beats·min -1 [90% CrI: - 18 to 4, Pd = 87%]. Changes in sweat rate were conflicting (0.01 L·h -1 [90% CrI: - 0.38 to 0.40, Pd = 53%]), primarily due to two studies demonstrating a reduction in sweat rate following heat acclimatisation., Conclusions: Data from athletes and military personnel relocating to a hotter climate were consistent with a reduction in resting core temperature and heart rate, in addition to an attenuated rise in core temperature and heart rate during an exercise-based heat response test. An increase in sweat rate is also attainable, with the extent of these adaptations dependent on WBGT, daily training duration and protocol length., Prospero Registration: CRD42022337761., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Background and Objective: Exercise in hot environments impairs endurance performance. Cooling interventions can attenuate the impact of heat stress on performance, but the influence of an exercise protocol on the magnitude of performance benefit remains unknown. This meta-analytical review compared the effects of pre- and per-cooling interventions on performance during self-paced and constant workload exercise in the heat., Methods: The study protocol was preregistered at the Open Science Framework ( https://osf.io/wqjb3 ). A systematic literature search was performed in PubMed, Web of Science, and MEDLINE from inception to 9 June, 2023. We included studies that examined the effects of pre- or per-cooling on exercise performance in male individuals under heat stress (> 30 °C) during self-paced or constant workload exercise in cross-over design studies. Risk of bias was assessed using the Cochrane Risk of Bias Tool for randomized trials., Results: Fifty-nine studies (n = 563 athletes) were identified from 3300 records, of which 40 (n = 370 athletes) used a self-paced protocol and 19 (n = 193 athletes) used a constant workload protocol. Eighteen studies compared multiple cooling interventions and were included more than once (total n = 86 experiments and n = 832 paired measurements). Sixty-seven experiments used a pre-cooling intervention and 19 used a per-cooling intervention. Average ambient conditions were 34.0 °C [32.3-35.0 °C] and 50.0% [40.0-55.3%] relative humidity. Cooling interventions attenuated the performance decline in hot conditions and were more effective during a constant workload (effect size [ES] = 0.62, 95% confidence interval [CI] 0.44-0.81) compared with self-paced exercise (ES = 0.30, 95% CI 0.18-0.42, p = 0.004). A difference in performance outcomes between protocols was only observed with pre-cooling (ES = 0.74, 95% CI 0.50-0.98 vs ES = 0.29, 95% CI 0.17-0.42, p = 0.001), but not per-cooling (ES = 0.45, 95% CI 0.16-0.74 vs ES = 0.35, 95% CI 0.01-0.70, p = 0.68)., Conclusions: Cooling interventions attenuated the decline in performance during exercise in the heat, but the magnitude of the effect is dependent on exercise protocol (self-paced vs constant workload) and cooling type (pre- vs per-cooling). Pre-cooling appears to be more effective in attenuating the decline in exercise performance during a constant workload compared with self-paced exercise protocols, whereas no differences were found in the effectiveness of per-cooling., (© 2023. The Author(s).)

Background: Repeated exposure to heat (ie, plasma volume expansion) or altitude (ie, increase in total hemoglobin mass), in conjunction with exercise, induces hematological adaptations that enhance endurance performance in each respective environment. Recently, combining heat and altitude training has become increasingly common for athletes preparing to compete in temperate, sea-level conditions., Purpose: To review the physiological adaptations to training interventions combining thermal and hypoxic stimuli and summarize the implications for temperate, sea-level performance. Current Evidence: To date, research on combining heat and hypoxia has employed 2 main approaches: simultaneously combining the stressors during training or concurrently training in the heat and sleeping at altitude, sometimes with additional training in hypoxia. When environmental stimuli are combined in a training session, improvements in aerobic fitness and time-trial performance in temperate, sea-level conditions are generally similar in magnitude to those observed with heat, or altitude, training alone. Similarly, training in the heat and sleeping at altitude does not appear to provide any additional hematological or nonhematological benefits for temperate; sea-level performance relative to training in hot, hypoxic, or control conditions., Conclusions: Current research regarding combined heat and altitude interventions does not seem to indicate that it enhances temperate, sea-level performance to a greater extent than "traditional" (heat or hypoxia alone) training approaches. A major challenge in implementing combined-stressor approaches lies in the uncertainty surrounding the prescription of dosing regimens (ie, exercise and environmental stress). The potential benefits of conducting heat and altitude exposure sequentially (ie, one after the other) warrants further investigation.

The aim of this audit was to quantify female representation in research on heat adaptation. Using a standardized audit tool, the PubMed database was searched for heat adaptation literature from inception to February 2023. Studies were included if they investigated heat adaptation among female and male adults (≥18-50 years) who were free from noncommunicable diseases, with heat adaptation the primary or secondary outcome of interest. The number and sex of participants, athletic caliber, menstrual status, research theme, journal impact factor, Altmetric score, Field-Weighted Citation Impact, and type of heat exposure were extracted. A total of 477 studies were identified in this audit, including 7,707 participants with ∼13% of these being female. Most studies investigated male-only cohorts (∼74%, n = 5,672 males), with ∼5% (n = 360 females) including female-only cohorts. Of the 126 studies that included females, only 10% provided some evidence of appropriate methodological control to account for ovarian hormone status, with no study meeting best-practice recommendations. Of the included female participants, 40% were able to be classified to an athletic caliber, with 67% of these being allocated to Tier 2 (i.e., trained/developmental) or below. Exercise heat acclimation was the dominant method of heat exposure (437 interventions), with 21 studies investigating sex differences in exercise heat acclimation interventions. We recommend that future research on heat adaptation in female participants use methodological approaches that consider the potential impact of sexual dimorphism on study outcomes to provide evidence-based guidelines for female athletes preparing for exercise or competition in hot conditions.

Objective: To quantify the impact of performing challenging cognitive, physical and psychological tasks on subsequent cognitive performance, and whether differences in performance are predicted by psychological variables., Background: Successful performance in many occupations depends on resilient cognition: the degree to which cognitive functions can withstand, or are resilient to, the effects of stress. Several studies have examined the effect of individual stressors on cognition; however, the capacity to compare different types of stress across studies is limited., Method: Fifty-eight participants completed cognitive, physical, psychological and control interventions, immediately preceded, and followed, by a battery of cognitive tasks. Self-efficacy and cognitive appraisal were reported at baseline. Perceived stress was recorded post-intervention. Subjective workload was recorded for each cognitive battery and intervention., Results: Cognitive performance was impaired by the cognitive, physical and psychological interventions, with the greatest effect following the cognitive intervention. The subjective workload reported for the post-intervention cognitive battery was higher following the cognitive and physical interventions. Neither self-efficacy, cognitive appraisal, perceived stress nor subjective workload of the intervention strongly predicted post-intervention performance., Conclusion: Given the differences among interventions and cognitive domains, it appears that challenges to resilient cognition are broad and varied, and the mechanism(s) by which impairment occurs is complex., Application: Considering the increase in subjective workload for the post-intervention cognitive battery, a combination of subjective and objective measures of cognitive performance monitoring should be considered., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Objectives: To assess the magnitude of seasonal heat acclimatisation in recreationally active adults and contextualise the process by documenting the factors that influence adaptations., Design: Longitudinal, repeated measures design., Methods: Seventeen (7 females) recreationally active adults (28 ± 8 yr, V̇O 2peak 54 ± 8 mL·kg -1 ·min -1 ) exercising outdoors a minimum of 5 h·wk -1 completed a 45-min heat response test running at 60 % V̇O 2peak in 40 °C and 30 % relative humidity prior to, midway through, and following summer. Self-reported physical activity diaries were completed at the beginning and end of summer. Daytime wet-bulb globe temperature was calculated for each day of summer. Data were analysed using Bayesian ordinal regressions., Results: Daytime wet-bulb globe temperature was 22.0 ± 4.4 °C, with the most common hour for recreational exercise being 17:00 to 18:00. Following summer, the rise in oesophageal temperature and mean skin temperature during the heat response test was lower by 0.12 °C [90 % credible interval: -0.30, 0.06; probability of direction = 87 %] and 0.43 °C [-0.74, -0.10; 98 %], respectively. Moreover, forearm local sweat rate increased by 0.26 mg·cm -2 ·min -1 [0.15, 0.36; 100 %]. There was minimal evidence of a change in the increase in heart rate (1 beat·min -1 [-3, 5; 62 %]), or whole-body sweat rate (0.03 L·h -1 [-0.11, 0.15; 68 %]) during the heat response test., Conclusions: Although there was evidence of partial heat adaptation in recreationally active adults following summer, a combination of exercising later in the day and the prevailing environmental conditions (La Niña in South-Eastern Australia) may have blunted the development of further adaptations., Competing Interests: Declaration of interest statement None., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Background: There is strong evidence for the benefits of exercise for people with Multiple Sclerosis (MS), however, up to 80% of people with MS report experiencing exacerbated symptoms with elevated body temperatures. A range of cooling garments to assist people with MS manage symptoms of heat sensitivity have been investigated. Therefore, the aim of this systematic review was to assess the effect of cooling garments to improve physical function in people with MS, and to determine any associated physiological and perceptual responses., Method: A systematic review adhering to the PRISMA guidelines was performed. The eligibility criteria required investigations to have conducted a randomized controlled trial or cross-over study to assess the effect of a cooling garment to improve physical function, or a related physiological or perceptual measure, in people with MS., Results: Thirteen empirical studies were identified, compromising of acute cross-over designs (61.5%), longitudinal parallel group designs (23.1%) or a combination of both (15.4%). The studies included 384 participants with MS with an expanded disability status scale range of 1-7.5. Garments included liquid-perfused cooling vests/tops/hoods (50.0%), phase-change cooling vests (38.9%), a cooling thigh-cuff (5.6%) and a palm cooling device (5.6%). The cooling garments were effective at improving walking capacity and functional mobility, and some studies demonstrated improvements in muscular strength and balance, but not manual dexterity. The garments also resulted in improved core temperature, skin temperature, thermal sensation and subjective fatigue. Improvements occurred in temperate and warm conditions, and both with and without an exercise stimulus., Discussion: Cooling garments can improve physical function for people with MS. Since none of the cooling garments caused harm, and no particular cooling garment could be identified as being superior, people with MS should experiment with different cooling garments to determine their preference, and industry should focus on cooling garments that are effective, accessible and user-friendly., Competing Interests: Declaration of Competing Interest The authors declare that there were no competing interests., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Population aging, high prevalence of non-communicable diseases, physical inactivity, and rising global temperatures are some of the most pressing issues in public health of the current century. Such trends suggest that individuals increasingly less equipped to tolerate heat will be increasingly exposed to it, which from a public health perspective is alarming. Nonetheless, future impacts of extreme heat events will depend not only on the magnitude of climate change, but on our ability to adapt by becoming less sensitive and vulnerable. Although physical activity's role in mitigating climate change has received attention, its potential contribution to climate change adaptation and resilience remains largely unaddressed. Accordingly, in this viewpoint, we discuss how regular physical activity throughout life could have an important contribution to adapting to rising global temperatures, allowing to be better equipped to cope with heat-related health hazards and increasing individual and community resilience. This viewpoint constitutes a call for more research into the contribution that physical activity can have in adapting to rising global temperatures and, more broadly, to climate change., Competing Interests: Declaration of interests J.D.P. has served as a consultant for The Coca Cola Company and Inuteq. No conflicts of interest, financial or otherwise, are declared by the authors., (Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.)

Purpose: To investigate the effects of a training camp with heat and/or hypoxia sessions on hematological and thermoregulatory adaptations., Methods: Fifty-six elite male rugby players completed a 2-week training camp with 5 endurance and 5 repeated-sprint sessions, rugby practice, and resistance training. Players were separated into 4 groups: CAMP trained in temperate conditions at sea level, HEAT performed the endurance sessions in the heat, ALTI slept and performed the repeated sprints at altitude, and H + A was a combination of the heat and altitude groups., Results: Blood volume across all groups increased by 140 mL (95%CI, 42-237; P = .006) and plasma volume by 97 mL (95%CI 28-167; P = .007) following the training camp. Plasma volume was 6.3% (0.3% to 12.4%) higher in HEAT than ALTI (P = .034) and slightly higher in HEAT than H + A (5.6% [-0.3% to 11.7%]; P = .076). Changes in hemoglobin mass were not significant (P = .176), despite a ∼1.2% increase in ALTI and H + A and a ∼0.7% decrease in CAMP and HEAT. Peak rectal temperature was lower during a postcamp heat-response test in HEAT (0.3 °C [0.1-0.5]; P = .010) and H + A (0.3 °C [0.1-0.6]; P = .005). Oxygen saturation upon waking was lower in ALTI (3% [2% to 5%]; P < .001) and H + A (4% [3% to 6%]; P < .001) than CAMP and HEAT., Conclusion: Although blood and plasma volume increased following the camp, sleeping at altitude impeded the increase when training in the heat and only marginally increased hemoglobin mass. Heat training induced adaptations commensurate with partial heat acclimation; however, combining heat training and altitude training and confinement during a training camp did not confer concomitant hematological adaptations.

Endurance exercise can disturb intestinal epithelial integrity, leading to increased systemic indicators of cell injury, hyperpermeability, and pathogenic translocation. However, the interaction between exercise, diet, and gastrointestinal disturbance still warrants exploration. This study examined whether a 6-day dietary intervention influenced perturbations to intestinal epithelial disruption in response to a 25-km race walk. Twenty-eight male race walkers adhered to a high carbohydrate (CHO)/energy diet (65% CHO, energy availability = 40 kcal·kg FFM-1·day-1) for 6 days prior to a Baseline 25-km race walk. Athletes were then split into three subgroups: high CHO/energy diet (n = 10); low-CHO, high-fat diet (LCHF: n = 8; <50 g/day CHO, energy availability = 40 kcal·kg FFM-1·day-1); and low energy availability (n = 10; 65% CHO, energy availability = 15 kcal·kg FFM-1·day-1) for a further 6-day dietary intervention period prior to a second 25-km race walk (Adaptation). During both trials, venous blood was collected pre-, post-, and 1 hr postexercise and analyzed for markers of intestinal epithelial disruption. Intestinal fatty acid-binding protein concentration was significantly higher (twofold increase) in response to exercise during Adaptation compared to Baseline in the LCHF group (p = .001). Similar findings were observed for soluble CD14 (p < .001) and lipopolysaccharide-binding protein (p = .003), where postexercise concentrations were higher (53% and 36%, respectively) during Adaptation than Baseline in LCHF. No differences in high CHO/energy diet or low energy availability were apparent for any blood markers assessed (p > .05). A short-term LCHF diet increased intestinal epithelial cell injury in response to a 25-km race walk. No effect of low energy availability on gastrointestinal injury or symptoms was observed.

Purpose: This study aimed to determine the effect of different air velocities on heat exchange and performance during prolonged self-paced exercise in the heat., Methods: Twelve male cyclists performed a 700-kJ time trial in four different air velocity conditions (still air, 16, 30, and 44 km·h -1 ) in 32°C and 40% relative humidity. Performance, thermal, cardiovascular, and perceptual responses were measured, and heat balance parameters were estimated using partitional calorimetry, including the maximum potential for sweat evaporation ( Emax )., Results: Mean power output was lower in still air (232 ± 42 W) than 16 (247 ± 30 W), 30 (250 ± 32 W), and 44 km·h -1 (248 ± 32 W; all P < 0.001), but similar between the 16-, 30-, and 44-km·h -1 air velocity conditions ( P ≥ 0.275). Emax was lower in still air (160 ± 13 W·m -2 ) than 16 (298 ± 25 W·m -2 ), 30 (313 ± 23 W·m -2 ), and 44 km·h -1 (324 ± 31 W·m -2 ) and lower in 16 than 44 km·h -1 (all P < 0.001). Peak core temperature was higher in still air (39.4°C ± 0.7°C) than 16 (39.0°C ± 0.45°C), 30 (38.8°C ± 0.3°C), and 44 km·h -1 (38.8°C ± 0.5°C; all P ≤ 0.002). Mean skin temperature was lower with greater airflow ( P < 0.001) but similar in 30 and 40 km·h -1 ( P = 1.00). Mean heart rate was ~2 bpm higher in still air than 44 km·h -1 ( P = 0.035). RPE was greater in still air than 44 km·h -1 ( P = 0.017)., Conclusions: Self-paced cycling in still air was associated with a lower Emax and subsequently higher thermal strain, along with a similar or greater cardiovascular strain, despite work rate being lower than in conditions with airflow. The similarity in performance between the 16-, 30-, and 44-km·h -1 air velocity conditions suggests that airflow ≥16 km·h -1 does not further benefit self-paced exercise performance in the heat because of modest improvements in evaporative efficiency., (Copyright © 2023 by the American College of Sports Medicine.)

Purpose: This study aimed to characterize the thermal and cardiovascular strain of professional cyclists during the 2019 Tour Down Under and determine the associations between thermal indices and power output, and physiological strain., Methods: Gastrointestinal temperature ( Tgi ), heart rate (HR), and power output were recorded during the six stages (129-151.5 km) of the Tour Down Under in ≤22 male participants. Thermal indices included dry-bulb, black-globe, wet-bulb, and wet-bulb-globe (WBGT) temperature; relative humidity (RH), Heat Index; Humidex; and universal thermal climate index. The heat stress index (HSI), which reflects human heat strain, was also calculated., Results: Dry-bulb temperature was 23°C-37°C, and RH was 18%-72% (WBGT: 21°C-29°C). Mean Tgi was 38.2°C-38.5°C, and mean peak Tgi was 38.9°C-39.4°C, both highest values recorded during stage 3 (WBGT: 27°C). Peak individual Tgi was ≥40.0°C in three stages and ≥39.5°C in 14%-33% of cyclists in five stages. Mean HR was 131-147 bpm (68%-77% of peak), with the highest mean recorded in stage 3 ( P ≤ 0.005). Mean power output was 180-249 W, with the highest mean recorded during stage 4 ( P < 0.001; 21°C WBGT). The thermal indices most strongly correlated with power output were black-globe temperature ( r = -0.778), RH ( r = 0.768), universal thermal climate index ( r = -0.762), and WBGT ( r = -0.745; all P < 0.001). Mean Tgi was correlated with wet-bulb temperature ( r = 0.495), HSI ( r = 0.464), and Humidex ( r = 0.314; all P < 0.05), whereas mean HR was most strongly correlated with HSI ( r = 0.720), along with Tgi ( r = 0.599) and power output ( r = 0.539; all P < 0.05)., Conclusions: Peak Tgi reached 40.0°C in some cyclists, although most remained <39.5°C with an HR of ~73% of peak. Power output was correlated with several thermal indices, primarily influenced by temperature, whereas Tgi and HR were associated with the HSI, which has potential for sport-specific heat policy development., (Copyright © 2022 by the American College of Sports Medicine.)

Paralympic athletes may be at increased risk for exertional heat illness (EHI) due to reduced thermoregulatory ability as a consequence of their impairment. This study investigated the occurrence of heat-stress related symptoms and EHI, and the use of heat mitigation strategies in Paralympic athletes, both in relation to the Tokyo 2020 Paralympic Games and previous events. Paralympic athletes competing in Tokyo 2020 were invited to complete an online survey five weeks prior to the Paralympics and up to eight weeks after the Games. 107 athletes (30 [24-38] years, 52% female, 20 nationalities, 21 sports) completed the survey. 57% of respondents had previously experienced heat-stress related symptoms, while 9% had been medically diagnosed with EHI. In Tokyo, 21% experienced at least one heat-stress related symptom, while none reported an EHI. The most common symptom and EHI were, respectively, dizziness and dehydration. In preparation for Tokyo, 58% of respondents used a heat acclimation strategy, most commonly heat acclimatization, which was more than in preparation for previous events (45%; P = 0.007). Cooling strategies were used by 77% of athletes in Tokyo, compared to 66% during past events ( P = 0.18). Cold towels and packs were used most commonly. Respondents reported no medically-diagnosed EHIs during the Tokyo 2020 Paralympic Games, despite the hot and humid conditions in the first seven days of competition. Heat acclimation and cooling strategies were used by the majority of athletes, with heat acclimation being adopted more often than for previous competitions., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.)

New Findings: What is the topic of this review? Exertional heat stroke epidemiology in sport and military settings, along with common risk factors and strategies and policies designed to mitigate its occurrence. What advances does it highlight? Individual susceptibility to exertional heat stroke risk is dependent on the interaction of intrinsic and extrinsic factors. Heat policies in sport should assess environmental conditions, as well as the characteristics of the athlete, clothing/equipment worn and activity level of the sport. Exertional heat stroke risk reduction in the military should account for factors specific to training and personnel., Abstract: Exertional heat illness occurs along a continuum, developing from the relatively mild condition of muscle cramps, to heat exhaustion, and in some cases to the life-threatening condition of heat stroke. The development of exertional heat stroke (EHS) is associated with an increase in core temperature stemming from inadequate heat dissipation to offset the rate of metabolically generated heat. Susceptibility to EHS is linked to the interaction of several factors including environmental conditions, individual characteristics, health conditions, medication and drug use, behavioural responses, and sport/organisational requirements. Two settings in which EHS is commonly observed are competitive sport and the military. In sport, the exact prevalence of EHS is unclear due to inconsistent exertional heat illness terminology, diagnostic criteria and data reporting. In contrast, exertional heat illness surveillance in the military is facilitated by standardised case definitions, a requirement to report all heat illness cases and a centralised medical record repository. To mitigate EHS risk, several strategies can be implemented by athletes and military personnel, including heat acclimation, ensuring adequate hydration, cold-water immersion and mandated work-to-rest ratios. Organisations may also consider developing sport or military task-specific heat stress policies that account for the evaporative heat loss requirement of participants, relative to the evaporative capacity of the environment. This review examines the epidemiology of EHS along with the strategies and policies designed to reduce its occurrence in sport and military settings. We highlight the nuances of identifying individuals at risk of EHS and summarise the benefits and shortcomings of various mitigation strategies., (© 2022 The Authors. Experimental Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.)

Both adult females and children have been reported to have a lower sweating capacity and thus reduced evaporative heat loss potential that may increase their susceptibility to exertional hyperthermia in the heat. Compared with males, females have a lower maximal sweat rate and thus a theoretically lower maximum skin wettedness due to a lower sweat output per gland. Similarly, children have been suggested to be disadvantaged in high ambient temperatures due to a lower sweat production and therefore reduced evaporative capacity, despite modifications of heat transfer due to physical attributes and possible evaporative efficiency. The reported reductions in the sudomotor activity of females and children suggest a lower sweating capacity in girls. However, because of the complexities of isolating sex and maturation from the confounding effects of morphological differences (e.g., body surface area-to-mass ratio) and metabolic heat production, limited evidence exists supporting whether children, and, more specifically, girls are at a thermoregulatory disadvantage. Furthermore, a limited number of child-adult comparison studies involve females and very few studies have directly compared regional and whole body sudomotor activity between boys and girls. This minireview highlights the exercise-induced sudomotor response of females and children, summarizes previous research investigating the sudomotor response to exercise in girls, and suggests important areas for further research.

Introduction: This study evaluated how single or combinations of weather parameters (temperature, humidity, wind speed, and solar load) affect peak performance during endurance running events and identified which events are most vulnerable to varying weather conditions., Methods: Results for the marathon, 50-km racewalking, 20-km racewalking, and 10,000-, 5000-, and 3000-m steeplechase were obtained from the official Web sites of large competitions. We identified meteorological data from nearby (8.9 ± 9.3 km) weather stations for 1258 races held between 1936 and 2019 across 42 countries, enabling analysis of 7867 athletes., Results: The wet bulb globe temperature (WBGT) across races ranged from -7°C to 33°C, with 27% of races taking place in cold/cool, 47% in neutral, 18% in moderate heat, 7% in high heat, and 1% in extreme heat conditions, according to the World Athletics classification. Machine learning decision trees (R2 = 0.21-0.58) showed that air temperature (importance score = 40%) was the most important weather parameter. However, when used alone, air temperature had lower predictive power (R2 = 0.04-0.34) than WBGT (R2 = 0.11-0.47). Conditions of 7.5°C-15°C WBGT (or 10°C-17.5°C air temperature) increased the likelihood for peak performance. For every degree WBGT outside these optimum conditions, performance declined by 0.3%-0.4%., Conclusion: More than one-quarter of endurance running events were held in moderate, high, or extreme heat, and this number reached one-half when marathons were excluded. All four weather parameters should be evaluated when aiming to mitigate the health and performance implications of exercising at high intensities in a hot environment with athletes adopting heat mitigation strategies when possible., (Copyright © 2021 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

Purpose: The effects of two different high-intensity training methods on 2,000 m rowing ergometer performance were examined in a feasibility study of 24 national-level rowers aged 18-27 years (17 males, 2,000 m ergometer time trial 6:21.7 ± 0:14.6 (min:s) and seven females, 2,000 m ergometer 7:20.3 ± 0:12.1. Habitual training for all participants was ~12-16 h per week). Methods : 16 high-intensity ergometer sessions were completed across two 3-week periods. Participants were allocated into two groups according to baseline 2,000 m time. High-intensity interval session-sprint-interval session (HIIT-SIT) completed eight HIIT (8 × 2.5 min intervals; 95% of 2,000 m wattage) followed by eight SIT (three sets of 7 × 30 s intervals; maximum effort). SIT-HIIT completed eight SIT sessions followed by eight HIIT sessions. Both a 2,000-m time trial and a progressive incremental test finishing with 4 min "all-out" performance were completed before and after each 3-week phase. Results: Both groups showed similar improvements in 2,000 m time and 4 min "all-out" distance after the first 3 weeks (2,000 m time: HIIT-SIT: -2.0 ± 0.6%, mean ± 90% CL, p  = 0.01; SIT-HIIT: -1.5 ± 0.3%, p  = 0.01) with no significant difference between groups. HIIT-SIT demonstrated the greatest improvements in submaximal heart rate (HR) during the progressive incremental test with eight sessions of HIIT showing a greater reduction in submaximal HR than eight sessions of SIT. The net improvement of 16 high-intensity sessions on 2,000 m time was -2.5% for HIIT-SIT (-10.6 ± 3.9 s, p  = 0.01) and - 2.2% for SIT-HIIT (-9.0 ± 5.7 s, p  = 0.01) and for 4 min "all-out" performance was 3.1% for HIIT-SIT (36 ± 25 m, p  = 0.01) and 2.8% for SIT-HIIT (33 ± 27 m, p  = 0.01). Conclusion: Eight sessions of high-intensity training can improve 2,000 m ergometer rowing performance in national-level rowers, with a further eight sessions producing minimal additional improvement. The method of high-intensity training appears less important than the dose., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Turner, Pyne, Périard and Rice.)

Permissive dehydration during exercise heat acclimation (HA) may enhance hematological and cardiovascular adaptations and thus acute responses to prolonged exercise. However, the independent role of permissive dehydration on vascular and cardiac volumes, ventricular-arterial (VA) coupling and systemic hemodynamics has not been systematically investigated. Seven males completed two 10-day exercise HA interventions with controlled heart rate (HR) where euhydration was maintained or permissive dehydration (-2.9 ± 0.5% body mass) occurred. Two experimental trials were conducted before and after each HA intervention where euhydration was maintained (-0.5 ± 0.4%) or dehydration was induced (-3.6 ± 0.6%) via prescribed fluid intakes. Rectal (T re ) and skin temperatures, HR, blood (BV) and left ventricular (LV) volumes, and systemic hemodynamics were measured at rest and during bouts of semi-recumbent cycling (55% V̇O 2 peak ) in 33°C at 20, 100, and 180 min. Throughout HA sweat rate (12 ± 9%) and power output (18 ± 7 W) increased ( P < 0.05), whereas T re was 38.4 ± 0.2°C during the 75 min of HR controlled exercise ( P = 1.00). Neither HA intervention altered resting and euhydrated exercising T re , BV, LV diastolic and systolic volumes, systemic hemodynamics, and VA coupling ( P > 0.05). Furthermore, the thermal and cardiovascular strain during exercise with acute dehydration post-HA was not influenced by HA hydration strategy. Instead, elevations in T re and HR and reductions in BV and cardiac output matched pre-HA levels ( P > 0.05). These findings indicate that permissive dehydration during exercise HA with controlled HR and maintained thermal stimulus does not affect hematological or cardiovascular responses during acute endurance exercise under moderate heat stress with maintained euhydration or moderate dehydration., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Travers, González-Alonso, Riding, Nichols, Shaw and Périard.)

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.

The effects of dry-bulb temperature on self-paced exercise performance, along with thermal, cardiovascular, and perceptual responses, were investigated by minimizing differences in the skin-to-air vapor pressure gradient ( P sk,sat - P a ) between four temperatures. Fourteen trained male cyclists performed 30-km time trials in 13°C and 44% relative humidity (RH), 20°C and 70% RH, 28°C and 78% RH, and 36°C and 72% RH. Power output was similar in 13°C (275 ± 31 W; means and SD) and 20°C (272 ± 28 W; P = 1.00), lower in 36°C (228 ± 36 W) than 13°C, 20°C, and 28°C (262 ± 27 W; P < 0.001) and lower in 28°C than at 13°C and 20°C ( P < 0.001). Peak rectal temperature was higher in 36°C (39.6 ± 0.4°C) than in all conditions ( P < 0.001) and higher in 28°C (39.1 ± 0.4°C) than 13°C (38.7 ± 0.3°C; P < 0.001) and 20°C (38.8 ± 0.3°C; P < 0.01). Mean heart rate was higher in 36°C (163 ± 14 beats·min -1 ) than all conditions ( P < 0.001) and higher in 20°C (156 ± 11 beats·min -1 ; P = 0.009) and 28°C (159 ± 11 beats·min -1 ; P < 0.001) than 13°C (153 ± 11 beats·min -1 ). Mean cardiac output was lower in 36°C (16.8 ± 2.5 L·min -1 ) than all conditions ( P < 0.001) and lower in 28°C (18.6 ± 1.6 L·min -1 ) than 20°C (19.4 ± 2.0 L·min -1 ; P = 0.004). Ratings of perceived exertion were higher in 36°C than all conditions ( P < 0.001) and higher in 28°C than 20°C ( P < 0.04). Self-paced exercise performance was maintained in 13°C and 20°C at a matched evaporative potential, impaired in 28°C, and further compromised in 36°C in association with a moderately lower evaporative potential and marked elevations in thermal, cardiovascular, and perceptual strain. NEW & NOTEWORTHY This is the first study to investigate the effects of dry-bulb temperature (13, 20, 28, and 36°C) on self-paced exercise performance by minimizing differences in the skin-to-air vapor pressure gradient (i.e., evaporative potential) between conditions. Performance was similar in 13°C and 20°C with a matched evaporative potential, whereas it was reduced at 28°C and further impaired at 36°C in association with a large decrease in dry heat loss and moderate reduction in evaporative potential.

Along with digestion and absorption of nutrients, the gastrointestinal epithelium acts as a primary intestinal defense layer, preventing luminal pathogens from entering the circulation. During exercise in the heat, epithelial integrity can become compromised, allowing bacteria and bacterial endotoxins to translocate into circulation, triggering a systemic inflammatory response and exacerbating gastrointestinal damage. While this relationship seems clear in the general population in endurance/ultraendurance exercise, the aim of this systematic review was to evaluate the effect of exercise in the heat on blood markers of gastrointestinal epithelial disturbance in well-trained individuals. Following the 2009 Preferred Reporting Items for Systematic Reviewed and Meta-Analyses guidelines, five electronic databases were searched for appropriate research, and 1,885 studies were identified. Five studies met the inclusion criteria and were subject to full methodological appraisal by two reviewers. Critical appraisal of the studies was conducted using the McMasters Critical Review Form. The studies investigated changes in markers of gastrointestinal damage (intestinal fatty acid-binding protein, endotoxin, and/or lipopolysaccharide-binding protein) following acute exercise in warm to hot conditions (≥ 30 °C) and included trained or well-trained participants with direct comparisons to a control temperate condition (≤ 22 °C). The studies found that prolonged submaximal and strenuous exercise in hot environmental conditions can acutely increase epithelial disturbance compared with exercise in cooler conditions, with disturbances not being clinically relevant. However, trained and well-trained populations appear to tolerate exercise-induced gastrointestinal disturbance in the heat. Whether this is an acquired tolerance related to regular training remains to be investigated.

Purpose: The risk of exercise-induced endotoxemia is increased in the heat and is primarily attributable to changes in gut permeability resulting in the translocation of lipopolysaccharides (LPS) into the circulation. The purpose of this study was to quantify the acute changes in gut permeability and LPS translocation during submaximal continuous and high-intensity interval exercise under heat stress., Methods: A total of 12 well-trained male runners (age 37 [7] y, maximal oxygen uptake [VO2max] 61.0 [6.8] mL·min-1·kg-1) undertook 2 treadmill runs of 2 × 15-minutes at 60% and 75% VO2max and up to 8 × 1-minutes at 95% VO2max in HOT (34°C, 68% relative humidity) and COOL (18°C, 57% relative humidity) conditions. Venous blood samples were collected at the baseline, following each running intensity, and 1 hour postexercise. Blood samples were analyzed for markers of intestinal permeability (LPS, LPS binding protein, and intestinal fatty acid-binding protein)., Results: The increase in LPS binding protein following each exercise intensity in the HOT condition was 4% (5.3 μg·mL-1, 2.4-8.4; mean, 95% confidence interval, P < .001), 32% (4.6 μg·mL-1, 1.8-7.4; P = .002), and 30% (3.0 μg·mL-1, 0.03-5.9; P = .047) greater than in the COOL condition. LPS was 69% higher than baseline following running at 75% VO2max in the HOT condition (0.2 endotoxin units·mL-1, 0.1-0.4; P = .011). Intestinal fatty acid-binding protein increased 43% (2.1 ng·mL-1, 0.1-4.2; P = .04) 1 hour postexercise in HOT compared with the COOL condition., Conclusions: Small increases in LPS concentration during exercise in the heat and subsequent increases in intestinal fatty acid-binding protein and LPS binding protein indicate a capacity to tolerate acute, transient intestinal disturbance in well-trained endurance runners.

Objective: To provide best-practice recommendations for developing and implementing heat-acclimatization strategies in secondary school athletics., Data Sources: An extensive literature review on topics related to heat acclimatization and heat acclimation was conducted by a group of content experts. Using the Delphi method, action-oriented recommendations were developed., Conclusions: A period of heat acclimatization consisting of ≥14 consecutive days should be implemented at the start of fall preseason training or practices for all secondary school athletes to mitigate the risk of exertional heat illness. The heat-acclimatization guidelines should outline specific actions for secondary school athletics personnel to use, including the duration of training, the number of training sessions permitted per day, and adequate rest periods in a cool environment. Further, these guidelines should include sport-specific and athlete-specific recommendations, such as phasing in protective equipment and reintroducing heat acclimatization after periods of inactivity. Heat-acclimatization guidelines should be clearly detailed in the secondary school's policy and procedures manual and disseminated to all stakeholders. Heat-acclimatization guidelines, when used in conjunction with current best practices surrounding the prevention, management, and care of secondary school student-athletes with exertional heat stroke, will optimize their health and safety., (© by the National Athletic Trainers' Association, Inc.)

Purpose: Hot-water immersion (HWI) after training in temperate conditions has been shown to induce thermophysiological adaptations and improve endurance performance in the heat; however, the potential additive effects of HWI and training in hot outdoor conditions remain unknown. Therefore, this study aimed to determine the effect of repeated postexercise HWI in athletes training in a hot environment., Methods: A total of 13 (9 female) elite/preelite racewalkers completed a 15-day training program in outdoor heat (mean afternoon high temperature = 34.6°C). Athletes were divided into 2 matched groups that completed either HWI (40°C for 30-40 min) or seated rest in 21°C (CON), following 8 training sessions. Pre-post testing included a 30-minute fixed-intensity walk in heat, laboratory incremental walk to exhaustion, and 10,000-m outdoor time trial., Results: Training frequency and volume were similar between groups (P = .54). Core temperature was significantly higher during immersion in HWI (38.5 [0.3]) than CON (37.8°C [0.2°C]; P < .001). There were no differences between groups in resting or exercise rectal temperature or heart rate, skin temperature, sweat rate, or the speed at lactate threshold 2, maximal O2 uptake, or 10,000-m performance (P > .05). There were significant (P < .05) pre-post differences for both groups in submaximal exercising heart rate (∼11 beats·min-1), sweat rate (0.34-0.55 L·h-1) and thermal comfort (1.2-1.5 arbitrary units), and 10,000-m racewalking performance time (∼3 min)., Conclusions: Both groups demonstrated significant improvement in markers of heat adaptation and performance; however, the addition of HWI did not provide further enhancements. Improvements in adaptation appeared to be maximized by the training program in hot conditions.

Purpose: To investigate whether including heat and altitude exposures during an elite team-sport training camp induces similar or greater performance benefits., Methods: The study assessed 56 elite male rugby players for maximal oxygen uptake, repeated-sprint cycling, and Yo-Yo intermittent recovery level 2 (Yo-Yo) before and after a 2-week training camp, which included 5 endurance and 5 repeated-sprint cycling sessions in addition to daily rugby training. Players were separated into 4 groups: (1) control (all sessions in temperate conditions at sea level), (2) heat training (endurance sessions in the heat), (3) altitude (repeated-sprint sessions and sleeping in hypoxia), and (4) combined heat and altitude (endurance in the heat, repeated sprints, and sleeping in hypoxia)., Results: Training increased maximal oxygen uptake (4% [10%], P = .017), maximal aerobic power (9% [8%], P < .001), and repeated-sprint peak (5% [10%], P = .004) and average power (12% [14%], P < .001) independent of training conditions. Yo-Yo distance increased (16% [17%], P < .001) but not in the altitude group (P = .562). Training in heat lowered core temperature and increased sweat rate during a heat-response test (P < .05)., Conclusion: A 2-week intensified training camp improved maximal oxygen uptake, repeated-sprint ability, and aerobic performance in elite rugby players. Adding heat and/or altitude did not further enhance physical performance, and altitude appears to have been detrimental to improving Yo-Yo.

Heat acclimation (HA) may improve the regulation of cardiac output (Q̇) through increased blood volume (BV) and left ventricular (LV) diastolic filling and attenuate reductions in Q̇ during exercise-induced dehydration; however, these hypotheses have never been directly tested. Before and following 10-days exercise HA, eight males completed two trials of submaximal exercise in 33°C and 50% relative humidity while maintaining preexercise euhydrated body mass (EUH; -0.6 ± 0.4%) or becoming progressively dehydrated (DEH; -3.6 ± 0.7%). Rectal (T re ) and skin (T sk ) temperatures, heart rate (HR), LV volumes and function, systemic hemodynamics and BV were measured at rest and during bouts of semirecumbent cycling (55% V̇o 2max ) at 20, 100 and 180 min, interspersed by periods of upright exercise. T re , BV, HR, LV volumes, LV systolic and diastolic function, and systemic hemodynamics were similar between trials at rest and during the first 20 min of exercise (all P > 0.05). These responses were largely unaffected by HA at 180 min in either hydration state. However, DEH induced higher T re (0.6 ± 0.3°C) and HR (16 ± 7 beats/min) and lower end-diastolic volume (29 ± 16 mL), stroke volume (26 ± 16 mL), and Q̇ (2.1 ± 0.8 L/min) compared with EUH at 180 min (all P < 0.05), yet LV twist and untwisting rate were increased or maintained ( P = 0.028 and 0.52, respectively). Findings indicate HA has minimal effects on LV volumes, LV mechanical function, and systemic hemodynamics during submaximal exercise in moderate heat, where HR and BV are similar. In contrast, DEH evokes greater hyperthermia and tachycardia, reduces BV, and impairs diastolic LV filling, lowering Q̇, regardless of HA state. NEW & NOTEWORTHY This study demonstrates that 10 days of exercise heat acclimation has minimal effects on left ventricular volumes, intrinsic cardiac function, and systemic hemodynamics during prolonged, repeated semirecumbent exercise in moderate heat, where heart rate and blood volume are similar to preacclimation levels. However, progressive dehydration is consistently associated with similar degrees of hyperthermia and tachycardia and reductions in blood volume, diastolic filling of the left ventricle, stroke volume, and cardiac output, regardless of acclimation state.