Pre-exercise hot water immersion increased circulatory heat shock proteins but did not alter muscle damage markers or endurance capacity after eccentric exercise.

Pre-exercise passive heating attenuates muscle damage caused by eccentric exercise in rats where the induction of heat shock proteins (HSPs) confers a myoprotective effect. We investigated whether pre-exercise hot water immersion (HWI) confers similar benefits in humans. Eleven recreational male athletes were immersed in 41°C water up to 60 min or until rectal temperatures reached 39.5°C. After a 6 h rest, the participants performed an eccentric downhill run for 1 h at -4% gradient to induce muscle damage. An endurance capacity test at 75% VO2max was conducted 18 h later. The control trial was similar except that participants were immersed at 34°C. Blood samples were collected to assess HSPs levels, creatine kinase, and lactate dehydrogenase activities. Plasma eHSP70 was higher post-immersion in HWI trials (1.3 ± 0.4 vs 1.1 ± 0.4; p = 0.005). Plasma eHSP27 was higher before (p = 0.049) and after (p = 0.015) endurance test in HWI. Leukocytic p-HSP27 was increased 18 h after HWI (0.97 ± 0.14 vs 0.67 ± 0.11; p = 0.04). Creatine kinase and lactate dehydrogenase activities were increased by 3-fold and 1.5-fold, respectively, after endurance test in HWI but did not differ across trials (p > 0.05). Mean heart rates were higher during eccentric run and endurance test in HWI as compared to control (p < 0.05). Endurance capacity was similar between trials (57.3 ± 11.5 min vs 55.0 ± 13.5 min; p = 0.564). Pre-exercise heating increased the expression of plasma eHSPs and leukocytic p-HSP27 but did not reduce muscle damage nor enhance endurance capacity.

Elevated brain temperature under severe heat exposure impairs cortical motor activity and executive function.

BACKGROUND: Excessive heat exposure can lead to hyperthermia in humans, which impairs physical performance and disrupts cognitive function. While heat is a known physiological stressor, it is unclear how severe heat stress affects brain physiology and function. METHODS: Eleven healthy participants were subjected to heat stress from prolonged exercise or warm water immersion until their rectal temperatures (Tre) attained 39.5°C, inducing exertional or passive hyperthermia, respectively. In a separate trial, blended ice was ingested before and during exercise as a cooling strategy. Data were compared to a control condition with seated rest (normothermic). Brain temperature (Tbr), cerebral perfusion, and task-based brain activity were assessed using magnetic resonance imaging techniques. RESULTS: Tbr in motor cortex was found to be tightly regulated at rest (37.3°C ± 0.4°C (mean ± SD)) despite fluctuations in Tre. With the development of hyperthermia, Tbr increases and dovetails with the rising Tre. Bilateral motor cortical activity was suppressed during high-intensity plantarflexion tasks, implying a reduced central motor drive in hyperthermic participants (Tre = 38.5°C ± 0.1°C). Global gray matter perfusion and regional perfusion in sensorimotor cortex were reduced with passive hyperthermia. Executive function was poorer under a passive hyperthermic state, and this could relate to compromised visual processing as indicated by the reduced activation of left lateral-occipital cortex. Conversely, ingestion of blended ice before and during exercise alleviated the rise in both Tre and Tbr and mitigated heat-related neural perturbations. CONCLUSION: Severe heat exposure elevates Tbr, disrupts motor cortical activity and executive function, and this can lead to impairment of physical and cognitive performance.

Climate change and population health in Singapore: a systematic review.

Gaseous emissions have contributed to global warming, an increase in the frequency of extreme weather events and poorer air quality. The associated health impacts have been well reported in temperate regions. In Singapore, key climate change adaptation measures and activities include coastal and flood protection, and mitigating heat impacts. We systematically reviewed studies examining climate variability and air quality with population health in Singapore, a tropical city-state in South-East Asia (SEA), with the aim to identify evidence gaps for policymakers. We included 14 studies with respiratory illnesses, cardiovascular outcomes, foodborne disease and dengue. Absolute humidity (3 studies) and rainfall (2 studies) were positively associated with adverse health. Extreme heat (2 studies) was inversely associated with adverse health. The effects of mean ambient temperature and relative humidity on adverse health were inconsistent. Nitrogen dioxide and ozone were positively associated with adverse health. Climate variability and air quality may have disease-specific, differing directions of effect in Singapore. Additional high quality studies are required to strengthen the evidence for policymaking. Research on effective climate action advocacy and adaptation measures for community activities should be strengthened. Funding: There was no funding source for this study.

The effects of low and normal dose ice slurry ingestion on endurance capacity and intestinal epithelial injury in the heat.

OBJECTIVES: Compare the effects of ice slurry ingestion at low and normal doses on endurance capacity and exertional heat stress-induced gastrointestinal perturbations. DESIGN: Randomised, cross-over design. METHODS: Twelve physically active males completed four treadmill running trials, ingesting ice slurry (ICE) or ambient drink (AMB) at 2 g·kg-1 (Normal; N) or 1 g·kg-1 (Low; L) doses every 15-min during exercise and 8 g·kg-1 (N) or 4 g·kg-1 (L) pre- and post-exercise. Pre-, during and post-exercise serum intestinal fatty-acid binding protein ([I-FABP]) and lipopolysaccharide ([LPS]) concentrations were determined. RESULTS: Pre-exercise gastrointestinal temperature (Tgi) was lower in L + ICE than L + AMB (p < 0.05), N + ICE than N + AMB (p < 0.001) and N + ICE than L + ICE (p < 0.001). Higher rate of Tgi rise (p < 0.05) and lower estimated sweat rate (p < 0.001) were observed in N + ICE than N + AMB. Rate of Tgi rise was similar at low dose (p = 0.113) despite a lower estimated sweat rate in L + ICE than L+AMB (p < 0.01). Time-to-exhaustion was longer in L + ICE than L + AMB (p < 0.05), but similar between N + ICE and N + AMB (p = 0.142) and L + ICE and N + ICE (p = 0.766). [I-FABP] and [LPS] were similar (p > 0.05). CONCLUSIONS: L + ICE elicited a lower heat dissipation compensatory effect with similar endurance capacity as N + ICE. Ice slurry conferred no protection against exertional heat stress-induced gastrointestinal perturbations.

Nutrition Recommendations for Table Tennis Players-A Narrative Review.

Table tennis (TT) is the second most popular racket sport globally and was the sixth most widely played Olympic sport in 2005. It is an indoor racket sport requiring a mixture of power, agility, alertness and fast reactions. Players need to move quickly around a table to receive the ball and produce powerful returns. New rules such as increased ball size and a change in ball material have changed the ball's trajectory, increasing the overall duration and intensity of game play. Scientific research on TT is growing but there has been no systematic review of nutrition for the sport. This review provides nutritional recommendations for TT athletes based on the physiological demands of TT, including energy expenditure during training and competitions, and the main metabolic pathways of TT. Guidelines on the daily intakes of carbohydrate, protein and fat are discussed in addition to hydration strategies. Micronutrients of concern for TT athletes include iron, magnesium and vitamin D and their recommended intakes are also provided. The timing and dose of ergogenic aids that may improve TT performance such as caffeine, creatine, lutein and zeaxanthin and beta-alanine are reviewed. Specific nutritional strategies for intakes leading up to competitions, post training and competition recovery and nutritional strategies for travel are also addressed.

Biomarkers for warfighter safety and performance in hot and cold environments.

Exposure to extreme environmental heat or cold during military activities can impose severe thermal strain, leading to impairments in task performance and increasing the risk of exertional heat (including heat stroke) and cold injuries that can be life-threatening. Substantial individual variability in physiological tolerance to thermal stress necessitates an individualized approach to mitigate the deleterious effects of thermal stress, such as physiological monitoring of individual thermal strain. During heat exposure, measurements of deep-body (Tc) and skin temperatures and heart rate can provide some indication of thermal strain. Combining these physiological variables with biomechanical markers of gait (in)stability may provide further insight on central nervous system dysfunction - the key criterion of exertional heat stroke (EHS). Thermal strain in cold environments can be monitored with skin temperature (peripheral and proximal), shivering thermogenesis and Tc. Non-invasive methods for real-time estimation of Tc have been developed and some appear to be promising but require further validation. Decision-support tools provide useful information for planning activities and biomarkers can be used to improve their predictions, thus maximizing safety and performance during hot- and cold-weather operations. With better understanding on the etiology and pathophysiology of EHS, the microbiome and markers of the inflammatory responses have been identified as novel biomarkers of heat intolerance. This review aims to (i) discuss selected physiological and biomechanical markers of heat or cold strain, (ii) how biomarkers may be used to ensure operational readiness in hot and cold environments, and (iii) present novel molecular biomarkers (e.g., microbiome, inflammatory cytokines) for preventing EHS.

Delineating the impacts of air temperature and humidity for endurance exercise.

NEW FINDINGS: What is the central question of this study? What are the independent effects of air temperature and humidity on performance, physiological and perceptual responses during endurance exercise? What is the main finding and its importance? When examined independently, elevated air temperature increased heat strain and impaired aerobic exercise performance, but to a lesser extent than has been reported previously. These findings highlight the importance of absolute humidity relative to temperature when exercising or working under severe heat stress. ABSTRACT: Many studies have reported that ambient heat stress increases physiological and perceptual strain and impairs endurance exercise, but effects of air temperature per se remain almost unexamined. Most studies have used matched relative humidity, thereby exponentially increasing absolute humidity (water content in air) concurrently with temperature. Absolute (not relative) humidity governs evaporative rate and is more important at higher work rates and air temperatures. Therefore, we examined the independent effects of air temperature and humidity on performance, thermal, cardiovascular and perceptual measures during endurance exercise. Utilizing a crossover design, 14 trained participants (7 females) completed 45 min fixed-intensity cycling (70% V ̇ O 2 peak ${\dot V_{{{\rm{O}}_{\rm{2}}}{\rm{peak}}}}$ ) followed by a 20-km time trial in each of four environments: three air temperatures at matched absolute humidity (Cool, 18°C; Moderate, 27°C; and Hot, 36°C; at 1.96 kPa, air velocity ∼4.5 m/s), and one at elevated humidity (Hot Humid, 36°C at 3.92 kPa). Warmer air caused warmer skin (0.5°C/°C; P < 0.001), higher heart rate (1 bpm/°C; P < 0.001), sweat rate (0.04 l/h/°C; P < 0.001) and thermal perceptions during fixed-intensity exercise, but minimally affected core temperature (<0.01°C/°C; P = 0.053). Time-trial performance was comparable between Cool and Moderate (95% CI: -1.4, 5.9%; P = 0.263), but 3.6-6% slower in Hot (95% CI: ±2.4%; P ≤ 0.006). Elevated humidity increased core temperature (P < 0.001), perceived temperature and discomfort but not skin temperature or heart rate, and reduced mean blood pressure (P = 0.046) during fixed-intensity exercise. Elevated humidity impaired time-trial performance by 3.4% (95% CI: ±2.2%; P = 0.006). In conclusion, these findings quantify the importance of absolute humidity alongside air temperature when exercising under severe heat stress.

Small changes in thermal conditions hinder marathon running performance in the tropics.

We examined marathon performance of the same group of runners in relation to small changes in dry bulb temperature (Tdb) and wet bulb temperature (Twb) across 3 consecutive y, and investigated whether performance was poorer during an evening marathon compared with morning marathons. Marathon results were obtained from the 2017, 2018, and 2019 Standard Chartered Singapore Marathons. Tdb, Twb, Td, relative humidity, and absolute humidity were gathered for each marathon. K-means clustering and linear regressions were performed on 610 runners who participated in all three marathons. Analysis of the 610 runners' marathon performance was contrasted with Tdb and Twb. Linear regressions were also performed on 190 runners filtered by percentile, yielding similar results. For clusters with similar Tdb from all runners K-means clustering, an increase in mean Twb by 1.5°C coincided with an increase in finishing time by 559 s (9.3 min) (p < 0.033). Twb hinders marathon performance more than Tdb, with each percentage rise in Tdb and Twb resulting in an increase in net time by 7.6% and 39.1%, respectively (p < 0.025). Male and female runners' response to Tdb and Twb changes were similar (overlap in 95% confidence intervals for the respective regression coefficients). In conclusion, small variations in environmental parameters affected marathon performance, with Twb impairing marathon performance more than Tdb. Marathon performance was likely better in the morning than evening, possibly due to time of day differences, along with unfavorable Tdb that superseded training effects and the effects of lower Twb.

Continuous Thermoregulatory Responses to a Mass-Participation 89-km Ultramarathon Road Race.

PURPOSE: To continuously measure body core temperature (Tc) throughout a mass-participation ultramarathon in subelite recreational runners to quantify Tc magnitude and the influence of aerobic fitness and body fat. METHODS: Twenty-three participants (19 men and 4 women; age 45 [9] y; body mass 72.0 [9.3] kg; body fat 26% [6%]; peak oxygen uptake 50 [6] mL·kg-1·min-1) had gastrointestinal temperature measured during an 89-km ultramarathon. Prerace-to-postrace changes in body mass, plasma sodium, and fluid and food recall quantified body water balance. RESULTS: In maximal environmental conditions of 26.3 °C and 53% humidity, 21 of the 23 participants finished in 10:28 (01:10) h:min while replacing 49% (27%) of sweat losses, maintaining plasma sodium (140 [3] mmol·L-1), and dehydrating by 4.1% (1.3%). Mean maximum Tc was 39.0 (0.5) (range 38.2-40.1 °C) with 90% of race duration ≤39.0 °C. Mean maximum ΔTc was 1.9 (0.9) (0.9-2.7 °C) with 95% of race duration ≤2.0 °C. Over 0 to 45 km, associations between ΔTc and peak oxygen uptake (positive) and body fat (negative) were observed. Over 58 to 89 km, associations between Tc and peak oxygen uptake (negative) and body fat (positive) were observed. CONCLUSIONS: Modest Tc responses were observed in recreational ultramarathon runners. Runners with higher levels of aerobic fitness and lower levels of body fat demonstrated the greatest changes in Tc during the first half of the race. Conversely, runners with lower levels of aerobic fitness and higher levels of body fat demonstrated the greatest absolute Tc in the final third of the race.

Exertional heat stroke: nutritional considerations.

NEW FINDINGS: What is the topic of this review? The potential role of nutrition in exertional heat stroke. What advances does it highlight? Certain nutritional and dietary strategies used by athletes and workers may exert a protective effect the pathophysiological processes of exertional heat stroke, whereas others may be detrimental. While current evidence suggests that some of these practices may be leveraged as a potential countermeasure to exertional heat stroke, further research on injury-related outcomes in humans is required. ABSTRACT: Exertional heat stroke (EHS) is a life-threatening illness and an enduring problem among athletes, military servicemen and -women, and occupational labourers who regularly perform strenuous activity, often under hot and humid conditions or when wearing personal protective equipment. Risk factors for EHS and mitigation strategies have generally focused on the environment, health status, clothing, heat acclimatization and aerobic conditioning, but the potential role of nutrition is largely underexplored. Various nutritional and dietary strategies have shown beneficial effects on exercise performance and health and are widely used by athletes and other physically active populations. There is also evidence that some of these practices may dampen the pathophysiological features of EHS, suggesting possible protection or abatement of injury severity. Promising candidates include carbohydrate ingestion, appropriate fluid intake and glutamine supplementation. Conversely, some nutritional factors and low energy availability may facilitate the development of EHS, and individuals should be cognizant of these. Therefore, the aims of this review are to present an overview of EHS along with its mechanisms and pathophysiology, discuss how selected nutritional considerations may influence EHS risk focusing on their impact on the key pathophysiological processes of EHS, and provide recommendations for future research. With climate change expected to increase EHS risk and incidence in the coming years, further investigation on how diet and nutrition may be optimized to protect against EHS would be highly beneficial.

Digitally-embroidered liquid metal electronic textiles for wearable wireless systems.

Electronic textiles capable of sensing, powering, and communication can be used to non-intrusively monitor human health during daily life. However, achieving these functionalities with clothing is challenging because of limitations in the electronic performance, flexibility and robustness of the underlying materials, which must endure repeated mechanical, thermal and chemical stresses during daily use. Here, we demonstrate electronic textile systems with functionalities in near-field powering and communication created by digital embroidery of liquid metal fibers. Owing to the unique electrical and mechanical properties of the liquid metal fibers, these electronic textiles can conform to body surfaces and establish robust wireless connectivity with nearby wearable or implantable devices, even during strenuous exercise. By transferring optimized electromagnetic patterns onto clothing in this way, we demonstrate a washable electronic shirt that can be wirelessly powered by a smartphone and continuously monitor axillary temperature without interfering with daily activities.

The use of sun-shade on safe heat exposure limit on a sunny summer day: a modelling study in Japan.

Sustainable methods are required to reduce the risks of thermal strain and heat-related illness without exacerbating greenhouse gas emissions. We investigated the effects of sun-shade use on safe heat exposure limit on a sunny summer day using historical climate data in Japan. We simulated a heat-acclimatised person standing at rest (metabolic heat production, 70 W·m-2) and during light work (100 W·m-2) on an asphalt pavement in the sun and sun-shade. Japan has three Köppen climate regions: tropical, temperate and cold. We analysed one city in the tropical region (24°N), three cities in the temperate region (31°N, 35°N and 39°N) and one city in the cold region (40°N). Hourly data were collected from 7 AM to 6 PM, June to September, from 2010 to 2019. The day with the longest daylight hours and the greatest solar radiation intensity was used for analysis. With sun-shade (a white polyester tarpaulin/awning), ambient temperature, global solar radiation and ground surface temperature were assumed to be 0.5°C, 45% and 6°C lower than in the sun, respectively. Sun-shade use eliminated the days with at least 1 hour exceeding safe heat exposure limit at rest in all cities. The same was observed for light work in the temperate and cold cities, although the tropical city had 2 days exceeding safe heat exposure limit during the decade. Sun-shade use on a sunny summer day can be an effective and sustainable method to reduce heat exposure hazard at rest and during light work in tropical, temperate and cold climate regions.

Changes in energy balance, body composition, metabolic profile and physical performance in a 62-day Army Ranger training in a hot-humid environment.

OBJECTIVES: To determine the physiological effects of multiple stressors including energy deficit during a 62-day Ranger course in a hot-humid environment. DESIGN: Prospective cohort design. METHODS: Food intake data were collected daily and energy expenditure at each of the three phases of the course was estimated by the doubly-labeled water method. Anthropometry, hydration status, stress and metabolic hormones, handgrip strength and lower explosive power were measured at the start and at the end of each phase. RESULTS: Seventeen male participants (age: 24.5 ±â€¯3.2 years, height: 173.9 ±â€¯5.1 cm, body mass: 69.3 ±â€¯3.2 kg, BMI: 22.9 ±â€¯0.9 kg/m2, percent body fat: 14 ±â€¯5%) completed the study. Mean total daily energy expenditure was 4756 kcal/day and mean daily energy intake was 3882 kcal/day. An 18% energy deficit resulted in an average body mass loss of 4.6 kg, comprising mostly fat mass. Participants with higher baseline adiposity (>15% body fat) lost more fat mass and gained (rather than lost) muscle mass compared to those with lower baseline adiposity. Handgrip strength declined only at the end of Phase I, while lower body explosive power declined progressively throughout the course. Lean mass in arms and legs was correlated with initial grip strength and lower body explosive power, but only at the start of the course. CONCLUSIONS: Physiologically demanding Ranger training in an equatorial environment is at least as metabolically demanding and stressful as other similar high-risk training courses, as demonstrated by the stress and metabolic endocrine responses, changes in body composition, and reduction in explosive power. Moreover, the smaller body size of Asian soldiers may confer an energetic advantage over larger sized Western counterparts.

Palatable Flavoured Fluids without Carbohydrates and Electrolytes Do Not Enhance Voluntary Fluid Consumption in Male Collegiate Basketball Players in the Heat.

Using palatable fluids to enhance drinking in athletes who display insufficient compensatory hydration behaviour may mitigate the risks of hypohydration and performance deficits. However, it is unclear whether flavour can independently enhance fluid consumption. This study examined the effects of a colourless, artificially sweetened flavoured water (FW), without carbohydrates and with negligible amounts of sodium, compared to plain water (W) on fluid consumption in male collegiate basketball players in a practical game setting. Eighteen male basketball players (age 23.1 ± 1.3 years) played a 3v3 basketball small-sided game. The players were randomly assigned to consume either FW or W. Pre-game urine-specific gravity, fluid consumption, body mass, and hedonic taste perceptions were assessed. Basketball performance was analysed through notational analysis. Ratings of perceived exertion and thirst were recorded at pre-, post-game, and at each rest period. Heart rate was recorded throughout the gameplay. Despite significantly higher hedonic ratings for FW than W (6.78 ± 0.83 vs. 5.56 ± 1.33, p = 0.033, d = 1.36), there were no significant differences in fluid consumption (1083 ± 32 mL vs. 1421 ± 403 mL, p = 0.068, d = 0.92). Our result highlighted that using palatable fluids as a strategy to increase fluid consumption during high-intensity gameplay in the heat may not be effective if used without carbohydrates and electrolytes. Practitioners could consider both fluid palatability and composition in establishing a hydration plan for athletes.

Hydration Status and Fluid Replacement Strategies of High-Performance Adolescent Athletes: An Application of Machine Learning to Distinguish Hydration Characteristics.

There are limited data on the fluid balance characteristics and fluid replenishment behaviors of high-performance adolescent athletes. The heterogeneity of hydration status and practices of adolescent athletes warrant efficient approaches to individualizing hydration strategies. This study aimed to evaluate and characterize the hydration status and fluid balance characteristics of high-performance adolescent athletes and examine the differences in fluid consumption behaviors during training. In total, 105 high-performance adolescent athletes (male: 66, female: 39; age 14.1 ± 1.0 y) across 11 sports had their hydration status assessed on three separate occasions-upon rising and before a low and a high-intensity training session (pre-training). The results showed that 20-44% of athletes were identified as hypohydrated, with 21-44% and 15-34% of athletes commencing low- and high-intensity training in a hypohydrated state, respectively. Linear mixed model (LMM) analyses revealed that athletes who were hypohydrated consumed more fluid (F (1.183.85)) = 5.91, (p = 0.016). Additional K-means cluster analyses performed highlighted three clusters: "Heavy sweaters with sufficient compensatory hydration habits," "Heavy sweaters with insufficient compensatory hydration habits" and "Light sweaters with sufficient compensatory hydration habits". Our results highlight that high-performance adolescent athletes with ad libitum drinking have compensatory mechanisms to replenish fluids lost from training. The approach to distinguish athletes by hydration characteristics could assist practitioners in prioritizing future hydration intervention protocols.

Thermoregulatory responses to ice slurry ingestion during low and moderate intensity exercises with restrictive heat loss.

OBJECTIVES: We investigated the thermoregulatory responses to ice slurry ingestion during low- and moderate-intensity exercises with restrictive heat loss. DESIGN: Randomised, counterbalanced, cross-over design. METHODS: Following a familiarisation trial, ten physically active males exercised on a motorised treadmill at low-intensity (L; 40% VO2max) or moderate-intensity (M; 70% VO2max) for 75-min, in four randomised, counterbalanced trials. Throughout the exercise bout, participants donned a raincoat to restrict heat loss. Participants ingested 2gkg-1 body mass of ambient water (L+AMB and M+AMB trials) or ice slurry (L+ICE and M+ICE trials) at 15-min intervals during exercise in environmental conditions of Tdb, 25.1±0.6°C and RH, 63±5%. Heart rate (HR), gastrointestinal temperature (Tgi), mean weighted skin temperature (Tsk), estimated sweat loss, ratings of perceived exertion (RPE) and thermal sensation (RTS) were recorded. RESULTS: Compared to L+AMB, participants completed L+ICE trials with lower ΔTgi (0.8±0.3°C vs 0.6±0.2°C; p=0.03), mean RPE (10±1 vs 9±1; p=0.03) and estimated sweat loss (0.91±0.2L vs 0.78±0.27L; p=0.04). Contrastingly, Tgi (p=0.22), Tsk (p=0.37), HR (p=0.31), RPE (p=0.38) and sweat loss (p=0.17) were similar between M+AMB and M+ICE trials. RTS was similar during both low-intensity (4.9±0.5 vs 4.7±0.3; p=0.10) and moderate-intensity exercise (5.3±0.47 vs 5.0±0.4; p=0.09). CONCLUSIONS: Per-cooling using ice slurry ingestion marginally reduced thermal strain during low-intensity but not during moderate-intensity exercise. Ice slurry may be an effective and practical heat mitigation strategy during low-intensity exercise such as in occupational and military settings, but a greater volume should be considered to ensure its efficacy.

Effect of regular precooling on adaptation to training in the heat.

PURPOSE: This study investigated whether regular precooling would help to maintain day-to-day training intensity and improve 20-km cycling time trial (TT) performed in the heat. Twenty males cycled for 10 day × 60 min at perceived exertion equivalent to 15 in the heat (35 °C, 50% relative humidity), preceded by no cooling (CON, n = 10) or 30-min water immersion at 22 °C (PRECOOL, n = 10). METHODS: 19 participants (n = 9 and 10 for CON and PRECOOL, respectively) completed heat stress tests (25-min at 60% [Formula: see text] and 20-km TT) before and after heat acclimation. RESULTS: Changes in mean power output (∆MPO, P = 0.024) and heart rate (∆HR, P = 0.029) during heat acclimation were lower for CON (∆MPO - 2.6 ± 8.1%, ∆HR - 7 ± 7 bpm), compared with PRECOOL (∆MPO + 2.9 ± 6.6%, ∆HR - 1 ± 8 bpm). HR during constant-paced cycling was decreased from the pre-acclimation test in both groups (P < 0.001). Only PRECOOL demonstrated lower rectal temperature (Tre) during constant-paced cycling (P = 0.002) and lower Tre threshold for sweating (P = 0.042). However, skin perfusion and total sweat output did not change in either CON or PRECOOL (all P > 0.05). MPO (P = 0.016) and finish time (P = 0.013) for the 20-km TT were improved in PRECOOL but did not change in CON (P = 0.052 for MPO, P = 0.140 for finish time). CONCLUSION: Precooling maintains day-to-day training intensity and does not appear to attenuate adaptation to training in the heat.