Neuropsychological determinants of exercise tolerance in the heat

A Menthol-Enhanced "Cooling" Energy Gel Does Not Influence Laboratory Time Trial Performance in Trained Runners

l-menthol (menthol) is an organic compound derived from peppermint which imparts a refreshing mint flavor and aroma to oral hygiene products, chewing gum, and topical analgesics. Menthol has been identified as a non-thermal sensory cooling strategy for athletes when ingested or mouth-rinsed during exercise in hot environments. Therefore, sports nutrition products delivering a controlled concentration of menthol could be beneficial for athletes exercising in the heat. We sought to test the performance and perceptual outcomes of a novel menthol energy gel during treadmill running in the heat (33 °C, 49% RH). Fourteen trained runners (mean ± SD; age: 31 ± 6 years, VO2max: 56.5 ± 10.1 mL·kg-1·min-1, BMI: 23.2 ± 2.4 kg/m2; six female) participated in a randomized, crossover, double-blind, and placebo-controlled study. A menthol-enhanced energy gel (0.5% concentration; MEN) or flavor-matched placebo (PLA) was ingested 5 min before and again at 20 and 40 min of a 40 min treadmill exercise preload at 60% VO2max, followed by a 20 min self-paced time trial. The total distance, vertical distance, perceptual measures (thermal comfort, thermal sensation, rating of perceived exertion, and affect), and cognitive performance via computerized neurocognitive assessment were measured. No difference between 20 min self-paced time trial total distance (MEN: 4.22 ± 0.54 km, PLA: 4.22 ± 0.55 km, p = 0.867), vertical distance (MEN: 49.2 ± 24.6 m, PLA: 44.4 ± 11.4 m, p = 0.516), or any perceptual measures was observed (all p > 0.05). Cognitive performance was not different between the trials (all p > 0.05). These results suggest that a menthol energy gel is not superior to a non-menthol gel in terms of performance or perception during treadmill running in the heat. More research is needed to confirm whether these findings translate to ecologically valid settings, including outdoor exercise in ambient heat and during competition.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Construct validity and invariance assessment of the social impacts of occupational heat stress scale (SIOHSS) among Ghanaian mining workers

Heat exposure studies over the last decade have shown little attention in assessing and reporting the psychometric properties of the various scales used to measure impacts of occupational heat stress on workers. A descriptive cross-sectional survey including 320 small- and large-scale mining workers was employed to assess the construct validity of the social impacts of occupational heat stress scale (SIOHSS) in the Western Region of Ghana in 2017. A confirmatory factor analysis (CFA) and invariance analysis were carried out using AMOS version 25 and statistical product and service solutions (SPSS) version 26 to examine the model fit and establish consistency correspondingly across multiple groups (gender, age, working hours, type of mining and workplace setting). Empirically, our results depicted that effects on health and safety, behavioural, productivity and social well-being were each found to be reliable, with Cronbach's α of 0.722, 0.807, 0.852 and 0.900 respectively. Though there were issues of insufficient discriminant validity as some average variance extract (AVE) were smaller than the corresponding maximum shared variance (MSV), the CFA showed good model fit indices (CFI = 0.856, GFI = 0.890, TLI = 0.863, SRMR = 0.08, RMSEA = 0.08). Also, the model was variant for all constrained aspects of the structural model indicating a requirement for an adaptation of the instrument across groups. The good to moderate internal consistency and construct validity of the SIOHSS is adequate evidence for the confidence required for its reliability and accuracy in measuring the social impacts of occupational heat stress on workers.

Face Cooling During Swimming Training in Tropical Condition

The aim of this study was to test the effect of face cooling with cold water (1.2 ± 0.7^°C) vs. face cooling with neutral water (28.0 ± 3.0^°C) during high-intensity swimming training on both the core temperature (T_co) and thermal perceptions in internationally ranked long-distance swimmers (5 men’s and 3 women’s) during 2 randomized swimming sessions. After a standardized warm-up of 1,200 m, the athletes performed a standardized training session that consisted of 2,000 m (5 × 400 m; start every 5’15”) at a best velocity then 600 m of aerobic work. Heart rate (HR) was continuously monitored during 5 × 400 m, whereas T_co, thermal comfort (TC), and thermal sensation (TS) were measured before and after each 400 m. Before and after each 400 m, the swimmers were asked to flow 200 mL of cold water (1.2^°C) or neutral (22^°C) water packaged in standardized bottles on their face. The swimmers were asked don’t drink during exercise. The velocity was significantly different between cold water and neutral water (p < 0.004 – 71.58 m.min^–1 ± 2.32 and 70.52 m.min^–1 ± 1.73, respectively). The T_co was increased by ±0.5^°C at race pace, under both face cooling conditions with no significant difference. No significant changes were noted in mean HR (i.e., 115 ± 9 and 114 ± 15 bpm for NW and CW, respectively). TC was higher with Cold Cooling than Neutral Cooling and TS was lower with Cold cooling compared with Neutral cooling. The changes in perceptual parameters caused by face cooling with cold water reflect the psychological impact on the physical parameters. The mean velocity was less important with face cooling whereas the heat rate and T_co were the same in the both conditions. The mechanism leading to these results seems to involve brain integration of signals from physiological and psychological sources.

Effect of acute heat stress on cognitive performance of chickens in a feed-related discriminant task

Little is known about immediate and long-lasting effect of acute heat stress on chicken cognition. Thirty-five, 9-week-old birds were trained to differentiate two cone colours; white (rewarded, R; with feed underneath) and black (unrewarded, UR; empty). The sixteen birds that learnt the task were randomly assigned to three temperature regimens (TR: 22-24 °C (control), 30-32 and 36-38 °C for 3h/day) for three consecutive days during which rectal (RT), wing (WT) and eye (ET) temperatures were monitored. After the 3 h of exposure, birds were allowed to rest for 1 h before the commencement of the discriminant task. The latencies to open the cones (R and UR) and proportion of cones opened were recorded. A long-lasting effect was tested a week after exposure to TR. TR had a significant effect on RT, WT and ET. The motivation to turn over R cones was weaker in birds exposed to 36-38 °C than birds exposed to 22-24 °C. Also, the proportion of R cones opened were fewer in birds that experienced TR of 36-38 °C compared to birds exposed to 22-24 °C and 30-32 °C specifically on two out of the three cognitive test days (Days 1 and 3). Latency and proportion of UR cones opened was not affected by TR. RT, WT and ET were all negatively and significantly correlated with latency to open the UR cones. Previous exposure of birds to three TR had no effect on the latency to open both cones but the proportion of R cones opened was greater in birds exposed to 30-32 °C compared to the 22-24 °C birds. In conclusion, an immediate (36-38 °C) and long-lasting effect (30-32 °C) of acute heat stress was associated with a weak motivation to perform feed related discrimination task.

Heat stress and physiological and perceptual strains of date harvesting workers in palm groves in Jiroft

BACKGROUND

Outdoor workers are exposed to heat caused by atmospheric conditions and solar radiation. More specifically, those working in palm groves are more in danger of heat stresses since they harvest their crops in hot seasons.

OBJECTIVE

This study was aimed at investigating heat stresses and strains in date harvesting workers in groves around Jiroft, Southeastern Iran.

METHODS

This study was a descriptive-analytical one of cross-sectional type. In this study, three environmental indices including Wet Bulb Globe Temperature index (WBGT), Environmental Stress Index (ESI) and Discomfort Index (DI), the physiological strain index (PSI) as well as perceptual strain index (PeSI) were analyzed to investigate stresses and strains in workers. For this purpose, 59 date harvesting workers (36 men and 23 women) in palm groves in Jiroft were analyzed. With accordance to date harvesting season, data collection was carried out from August to September, 2017.

RESULTS

In this research, the means of environmental indices including WBGT, ESI and DI were 32.77°C, 30.39°C and 33.22°C, respectively and they all revealed direct and significant correlation. Moreover, Time-Weighted Average for Wet Bulb Globe Temperature index (WBGT.TWA) was significantly different from Threshold Limit Values for Wet Bulb Globe Temperature index (WBGT.TLV). The scores of the PSI and PeSI were 2.28 and 6.61, respectively.

CONCLUSION

The results of this study indicated that date picking workers were exposed to heat stress more than the reference value of WBGT recommended by American Conference of Governmental Industrial Hygienists (ACGIH). In addition, workers suffered a low degree of physiological strain and a moderate degree of perceptual strain caused by heat stress in palm groves in Jiroft.

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

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

Fractional Contribution of Wildland Firefighters' Personal Protective Equipment on Physiological Strain

Activities performed by wildland firefighters are carried out wearing a personal protective equipment (PPE). Although the PPE protects workers from a wide variety of hazards, it may increase their physiological response and limit their performance. The aim of this study was to analyze the effect of the protective clothing (PPC) and the rest of the PPE elements (i.e., helmet, neck shroud, gloves, goggles, and mid-calf leather boots) on the wildland firefighters' thermophysiological response during a moderate-intense exercise. Six male wildland firefighters performed, in a counterbalanced order, a 120 min graded exercise test wearing three different clothing configurations: (i) a traditional short sports gear (SG), (ii) a PPC, and (iii) a complete firefighters' PPE. Trials were conducted on separate days at the same time of the day (12:00-15:00 h) and under climate-controlled conditions (∼30°C and ∼30% relative humidity). Heart rate, respiratory gas exchange, gastrointestinal and skin temperature, blood lactate concentration were recorded throughout the tests. Additionally, parameters of heat balance were estimated. Exercise time was shorter (p < 0.001) wearing the PPE (62.4 ± 13.3 min) than with the PPC (115.5 ± 5.0 min) and SG (118.2 ± 20.7 min). The increment of gastrointestinal temperature with the PPE (1.8 ± 0.3°C) was greater (p < 0.05) than the observed in PPC (1.2 ± 0.6°C) and SG (1.0 ± 0.2°C). The use of PPC increased (p < 0.05) subjects' metabolic demand and skin temperature versus SG during the last 20 min of the test. The sweat retention in the PPE (1,045.7 ± 214.7 g) and PPC (978.3 ± 330.6 g) was significantly higher than that obtained in the SG (510.0 ± 210.0 g). Sweat efficiency decreased (p < 0.05) in the following order: PPE (45.6 ± 18.3%), PPC (64.3 ± 7.8%), and SG (79.3 ± 7.0%). These results highlight the importance of the PPE elements in the subjects' thermal strain. The reduction in the sweat evaporation produced by the PPE, together with the ensemble mass caused a substantial increase in the subjects' thermophysiological response. As a consequence the performance was reduced by ∼50%.

An integrated approach to develop, validate and operate thermo-physiological human simulator for the development of protective clothing

Following the growing interest in the further development of manikins to simulate human thermal behaviour more adequately, thermo-physiological human simulators have been developed by coupling a thermal sweating manikin with a thermo-physiology model. Despite their availability and obvious advantages, the number of studies involving these devices is only marginal, which plausibly results from the high complexity of the development and evaluation process and need of multi-disciplinary expertise. The aim of this paper is to present an integrated approach to develop, validate and operate such devices including technical challenges and limitations of thermo-physiological human simulators, their application and measurement protocol, strategy for setting test scenarios, and the comparison to standard methods and human studies including details which have not been published so far. A physical manikin controlled by a human thermoregulation model overcame the limitations of mathematical clothing models and provided a complementary method to investigate thermal interactions between the human body, protective clothing, and its environment. The opportunities of these devices include not only realistic assessment of protective clothing assemblies and equipment but also potential application in many research fields ranging from biometeorology, automotive industry, environmental engineering, and urban climate to clinical and safety applications.

Comparison of Gastrointestinal and Rectal Temperatures During Recovery After a Warm-Weather Road Race

CONTEXT

It has been well established that gastrointestinal temperature (TGI) tracks closely with rectal temperature (TREC) during exercise. However, the field use of TGI pills is still being examined, and little is known about how measurements obtained using these devices compare during recovery after exercise in warm weather.

OBJECTIVE

To compare TGI and TREC in runners who completed an 11.3-km warm-weather road race and determine if runners with higher TGI and TREC present with greater passive cooling rates during recovery.

DESIGN

Cross-sectional study.

SETTING

Field.

PATIENTS OR OTHER PARTICIPANTS

Thirty recreationally active runners (15 men, 15 women; age = 39 ± 11 years, weight = 68.3 ± 11.7 kg, body fat = 19.2% ± 5.0%).

MAIN OUTCOME MEASURE(S)

The TGI and TREC were obtained immediately after the race and during a 20-minute passive rest at the 2014 Falmouth Road Race (heat index = 26.2°C ± 0.9°C). Temperatures were taken every 2 minutes during passive rest. The main dependent variables were mean bias and limits of agreement for TGI and TREC, using Bland-Altman analysis, and the 20-minute passive cooling rates for TGI and TREC.

RESULTS

No differences were evident between TGI and TREC throughout passive rest (P = .542). The passive cooling rates for TGI and TREC were 0.046 ± 0.031°C·min(-1) and 0.060 ± 0.036°C·min(-1), respectively. Runners with higher TGI and TREC at the start of cooling had higher cooling rates (R = 0.682, P < .001 and R = 0.54, P = .001, respectively). The mean bias of TGI during the 20-minute passive rest was -0.06°C ± 0.56°C with 95% limits of agreement of ±1.09°C.

CONCLUSIONS

After participants completed a warm-weather road race, TGI provided a valid measure of body temperature compared with the criterion measure of TREC. Therefore, TGI may be a viable option for monitoring postexercise-induced hyperthermia, if the pill is administered prophylactically.

Reduction in body temperature using hand cooling versus passive rest after exercise in the heat

OBJECTIVES

To examine the effects of hydration and hand cooling on lowering body temperature after exercise in the heat.

DESIGN

Randomized cross-over design.

METHODS

Nine recreationally active male participants (mean±SD; age, 24±4; height, 177.3±9.9cm; body mass, 76.7±11.6kg; body fat, 14.7±5.8%) completed a bout of treadmill exercise in a hot environment. After completion of exercise, participants were assigned to the following trials for post-exercise cooling: (1) hydrated with passive rest (HY), (2) hydrated with hand cooling on both hands (HY+2HC), (3) dehydrated with passive rest (DY), and (4) dehydrated with hand cooling on both hands (DY+2HC). Within subject differences were assessed using a three-way (Hydration×Condition×Time) repeated measures ANOVA with Tukey's post hoc analysis if significant interactions were found.

RESULTS

Irrespective of hydration status, hand cooling on both hands resulted in significantly greater reductions in T_REC than passive cooling at minute 20 (0.27°C [0.05, 0.49], ES=2.08, p=0.017) (Fig. 1). The reduction in T_REC at minute 18 trended towards statistical significance (0.21°C [.003, .42], ES=1.59, p=0.053). Hydration status alone and when differentiated among modes of cooling showed no differences on changes of T_REC or heart rate across all conditions during post exercise recovery (p>0.05).

CONCLUSIONS

Hand cooling on both hands reduced T_REC more than passive cooling, however, the cooling rates observed render hand cooling a poor option for cooling. Greater reductions in T_REC after exercise or between bouts of exercise may enhance recovery and subsequent performance.

Validation of Perceptual Strain Index to Evaluate the Thermal Strain in Experimental Hot Conditions

Background:

The incidence of heat stress is one of the most common problems in workplaces and industries. Many heat stress indices have been developed, and these indices have some disadvantages. The purpose of this study is to validate the perceptual strain index (PeSI) in experimental hot conditions.

Methods:

This study is of cross-sectional carried out on 15 men at five different thermal conditions (35°C, 30°C, 27°C, 24°C, and 21°C) in a climate chamber and on a treadmill at three levels of light (2.4 kph), medium (4.8 kph) and heavy activity (6.3 kph). Heart rate and oral temperature were respectively measured to calculate the physiological strain index. Also, thermal sensation and rate perceive exertion were respectively measured to calculate the PeSI. Finally, the correlation between the indices was analyzed using Pearson correlation test and regression analysis.

Results:

Pearson correlation test showed a high correlation (r = 0.94) between the PeSI and physiological strain index (P = 0/001). It was also observed a high correlation between the PeSI and the oral temperature (r = 0.78, P = 0/001) and the heart rate (r = 0.90, P = 0/001). In addition, there was found a moderate correlation (r = 0.71) between the PeSI and the wet bulb glob temperature (P = 0/001). However, there was no correlation between the PeSI and the body mass index (r = 0.0009, P = 0.79).

Conclusions:

The research findings showed when there is no access to other forms of methods to evaluate the heat stress, it can be used the PeSI in evaluating the strain because of its favorable correlation with the thermal strain.

Practical on-site measurement of heat strain with the use of a perceptual strain index

OBJECTIVES

There have been increased interests in research on quantifying heat strain of construction workers and formulating corresponding guidelines for working in hot weather. The aim of this study was to validate a subjective measurement tool, the perceptual strain index (PeSI), for measuring heat strain in real-work settings.

METHODS

A total of sixteen construction workers were invited to participate in the field surveys. Empiric-based human monitoring was carried out with simultaneous micrometeorological (wet-bulb globe temperature, WBGT), physiological (heart rate, HR), and perceptual (perceived exertion, RPE; thermal sensation, TS) measurements throughout the test. The relative heart rate (RHR), the physiological strain index (PSIHR), and the PeSI were then calculated accordingly.

RESULTS

The PeSI exhibited moderate correlations with WBGT and RHR (r = 0.42 and 0.40, respectively), which indicated the PeSI was sensitive to the variants of WBGT and RHR. The results of regression analysis indicated that the PeSI changed in the same general manner as the PSIHR, with a relatively large determination coefficient (R(2) = 0.67). The established perceptual strain zone illustrated that the PeSI ranging from 7 to 8 would be the exposure limit of construction workers in hot weather.

CONCLUSION

The PeSI is a simple, robust, reliable, and user-friendly tool for heat strain assessment in occupational settings. The perceptual strain zone will provide practical guidelines for on-site heat strain monitoring for construction workers.

Ingestion of a cold temperature/menthol beverage increases outdoor exercise performance in a hot, humid environment

Purpose

A recent laboratory study demonstrated that the ingestion of a cold/menthol beverage improved exercise performance in a hot and humid environment during 20 km of all-out cycling. Therefore, the aim of this study was to determine whether the ingestion of cold water/ice-slurry with menthol would improve performance in hot and humid outdoor conditions.

Methods

Ten trained males completed three trials of five blocks consisting of 4-km cycling and 1.5-km running. During warm-up, every block and recovery, the athletes drank 190 ml of aromatized (i.e., with 0.05 mL of menthol) beverage at three temperatures: Neutral (ambient temperature) (28.7°C±0. 5°C), Cold (3.1°C±0.6°C) or Ice-slurry (0.17°C±0.07°C). Trial time, core temperature (T_co), heart rate (HR), rate of perceived exertion (RPE), thermal sensation (TS) and thermal comfort (TC) were assessed.

Results

Ice-slurry/menthol increased performance by 6.2% and 3.3% compared with neutral water/menthol and cold water/menthol, respectively. No between-trial differences were noted for T_co, HR, RPE, TC and TS was lower with ice-slurry/menthol and cold water/menthol compared with neutral water/menthol.

Conclusion

A low drink temperature combined with menthol lessens the performance decline in hot/humid outdoor conditions (i.e., compared with cold water alone). Performances were better with no difference in psycho-physiological stress (T_co, HR and RPE) between trials. The changes in perceptual parameters caused by absorbing a cold/menthol beverage reflect the psychological impact. The mechanism leading to these results seems to involve brain integration of signals from physiological and psychological sources.

Managing Heat and Immune Stress in Athletes With Evidence-Based Strategies

Heat and immune stress can affect athletes in a wide range of sports and environmental conditions. The classical thermoregulatory model of heat stress has been well characterized, as has a wide range of practical strategies largely centered on cooling and heat-acclimation training. In the last decade evidence has emerged of an inflammatory pathway that can also contribute to heat stress. Studies are now addressing the complex and dynamic interplay between hyperthermia, the coagulation cascade, and a systemic inflammatory response occurring after transient damage to the gastrointestinal tract. Damage to the intestinal mucosal membrane increases permeability, resulting in leakage of endotoxins into the circulation. Practical strategies that target both thermoregulatory and inflammatory causes of heat stress include precooling; short-term heat-acclimation training; nutritional countermeasures including hydration, energy replacement, and probiotic supplementation; pacing strategies during events; and postevent cooling measures. Cooperation between international, national, and local sporting organizations is required to ensure that heat-management policies and strategies are implemented effectively to promote athletes’ well-being and performance.

Physical and perceptual cooling with beverages to increase cycle performance in a tropical climate

Purpose

This study compares the effects of neutral temperature, cold and ice-slush beverages, with and without 0.5% menthol on cycling performance, core temperature (T_co) and stress responses in a tropical climate (hot and humid conditions).

Methods

Twelve trained male cyclists/triathletes completed six 20-km exercise trials against the clock in 30.7°C±0.8°C and 78%±0.03% relative humidity. Before and after warm-up, and before exercise and every 5 km during exercise, athletes drank 190 mL of either aromatized (i.e., with 0.5 mL of menthol (5 gr/L)) or a non-aromatized beverage (neutral temperature: 23°C±0.1°C, cold: 3°C±0.1°C, or ice-slush: −1°C±0.7°C). During the trials, heart rate (HR) was continuously monitored, whereas core temperature (T_co), thermal comfort (TC), thermal sensation (TS) and rate of perceived exertion (RPE) were measured before and after warm-up, every 5 km of exercise, and at the end of exercise and after recovery.

Results

Both the beverage aroma (P<0.02) and beverage temperature (P<0.02) had significant and positive effects on performance, which was considerably better with ice-slush than with a neutral temperature beverage, whatever the aroma (P<0.002), and with menthol vs non-menthol (P<0.02). The best performances were obtained with ice-slush/menthol and cold/menthol, as opposed to neutral/menthol. No differences were noted in HR and T_co between trials.

Conclusion

Cold water or ice-slush with menthol aroma seems to be the most effective beverage for endurance exercise in a tropical climate. Further studies are needed to explore its effects in field competition.

Validation of the Omni Scale of Thermal Sensations

Concurrent and construct validation of the OMNI Scale of Thermal Sensations was examined in a sample of 16 adult men and 5 adult women. Concurrent validity was established by regressing OMNI ratings of thermal sensation against core and skin temperatures obtained during treadmill walking while wearing firefighter thermal-protective clothing in temperatures between 33 and 35°C. Construct validity was established by regressing the OMNI scale against a construct-specific visual analogue scale. OMNI scale responses accounted for statistically significant variance in both skin temperature and core temperature (48% and 51%, respectively) and visual analogue scale responses (84%). Concurrent and construct validity were established for the OMNI Scale of Thermal Sensations in healthy adults performing treadmill walking while wearing fire fighter thermal protective clothing.

Pre-cooling and sports performance: a meta-analytical review

Pre-cooling is used by many athletes for the purpose of reducing body temperature prior to exercise and, consequently, decreasing heat stress and improving performance. Although there are a considerable number of studies showing beneficial effects of pre-cooling, definite conclusions on the effectiveness of pre-cooling on performance cannot yet be drawn. Moreover, detailed analyses of the specific conditions under which pre-cooling may be most promising are, so far, missing. Therefore, we conducted a literature search and located 27 peer-reviewed randomized controlled trials, which addressed the effects of pre-cooling on performance. These studies were analysed with regard to performance effects and several test circumstances (environmental temperature, test protocol, cooling method, aerobic capacity of the subjects). Eighteen studies were performed in a hot (>26°C) environment and eight in a moderate. The cooling protocols were water application (n = 12), cooling packs (n = 3), cold drinks (n = 2), cooling vest (n = 6) and a cooled room (n = 4). The following different performance tests were used: short-term, high-intensity sprints (n = 2), intermittent sprints (n = 6), time trials (n = 10), open-end tests (n = 7) and graded exercise tests (n = 2). If possible, subjects were grouped into different aerobic capacity levels according to their maximal oxygen consumption (VO(2max)): medium 55-65 mL/kg/min (n = 11) and high >65 mL/kg/min (n = 6). For all studies the relative changes of performance due to pre-cooling compared with a control condition, as well as effect sizes (Hedges' g) were calculated. Mean values were weighted according to the number of subjects in each study. Pre-cooling had a larger effect on performance in hot (+6.6%, g = 0.62) than in moderate temperatures (+1.4%, g = 0.004). The largest performance enhancements were found for endurance tests like open-end tests (+8.6%, g = 0.52), graded exercise tests (+6.0%, g = 0.44) and time trials (+4.2%, g = 0.44). A similar effect was observed for intermittent sprints (+3.3%, g = 0.43), whereas performance changes were smaller during short-term, high-intensity sprints (-0.5%, g = 0.03). The most promising cooling methods were cold drinks (+15.0%, g = 1.68), cooling packs (+5.6%, g = 0.70) and a cooled room (+10.7%, g = 0.49), whereas a cooling vest (+4.8%, g = 0.31) and water application (+1.2%, g = 0.21) showed only small effects. With respect to aerobic capacity, the best results were found in the subjects with the highest VO(2max) (high +7.7%, g = 0.65; medium +3.8%, g = 0.27). There were four studies analysing endurance-trained athletes under time-trial conditions, which, in a practical sense, seem to be most relevant. Those studies found an average effect on performance of 3.7% (g = 0.48). In summary, pre-cooling can effectively enhance endurance performance, particularly in hot environments, whereas sprint exercise is barely affected. In particular, well trained athletes may benefit in a typical competition setting with practical and relevant effects. With respect to feasibility, cold drinks, cooling packs and cooling vests can be regarded as best-practice methods.

Peripheral markers of central fatigue in trained and untrained during uncompensable heat stress

The development of fatigue is more pronounced in the heat than thermoneutral environments; however, it is unclear whether biomarkers of central fatigue are consistent with the higher core temperature (T (c)) tolerated by endurance trained (TR) versus untrained (UT) during exertional heat stress (EHS). The purpose of this study was to examine the indicators of central fatigue during EHS in TR versus UT. Twelve TR and 11 UT males (mean ± SE [Formula: see text] = 70 ± 2 and 50 ± 1 mL kg LBM(-1) min(-1), respectively) walked on a treadmill to exhaustion (EXH) in 40°C (dry) wearing protective clothing. Venous blood was obtained at PRE and 0.5°C T (c) increments from 38 to 40°C/EXH. Free tryptophan (f-TRP) decreased dramatically at 39.5°C for the TR. Branch chain amino acids decreased with T (c) and were greater for UT than TR at EXH. Tyrosine and phenylalanine remained unchanged. Serum S100β was undetectable (<5 pg mL(-1)). Albumin was greater for the UT from PRE to 39.0°C and at EXH. Prolactin (PRL) responded to relative thermal strain with similar EXH values despite higher T (c) tolerated for TR (39.7 ± 0.09°C) than UT (39.0 ± 0.09°C). The high EXH PRL values for both groups support its use as a biomarker of the serotonin and dopamine interplay within the brain during the development of central fatigue.

Cognitive function in hot environments: a question of methodology

The physiological responses of thermal stress and its consequences on health have been well documented. However, the effect on cognitive function remains equivocal despite a substantial number of studies conducted in the area. Methodological discrepancies across different studies have made it difficult to conclude whether or not heat exposure per se has an adverse effect upon cognitive function and under what specific environmental and physiological conditions these alterations appear. This article gives an overview of the different confounding factors that have made it difficult to make conclusive interpretations. In addition, the current state of knowledge is presented and discussed with reference to the Global Workspace theory. Although previously presented conclusions are promising, much remains to be completed before understanding the mechanisms that could explain the relationship between heat exposure and cognitive function. Finally, recommendations are presented for further research in this area.

Alterations in cognitive performance during passive hyperthermia are task dependent

The objectives of this study were to (1) assess the effect of passive heating upon attention and memory task performance, and (2) evaluate the effectiveness of the application of cold packs to the head on preserving these functions. Using a counter-balance design 16 subjects underwent three trials: a control (CON, 20°C, 40% rH), hot (HOT, 50°C, 50% rH) and hot with the head kept cool (HHC). In each condition, three attention tests and two memory tests were performed. Mean core, forehead and tympanic temperatures were all significantly higher (p < 0.05) during HOT (38.6° ±0.1°, 39.6° ± 0.2° and 38.8°±0.1°C, respectively) and HHC (38° ± 0.2, 37.7° ± 0.3° and 37.7°C, respectively) than in CON (37.1° ± 0.6°, 33.3° ± 0.2° and 35.9° ± 0.3°C, respectively). Results indicate that there was impairment in working memory with heat exposure (p < 0.05) without alteration in attentional processes. The regular application of cold packs only prevented the detrimental effect of hyperthermia on short-term memory. Our results show that impairments in cognitive function with passive hyperthermia and the beneficial effect of head cooling are task dependent and suggests that exposure to a hot environment is a competing variable to the cognitive processes.