Heat Illness in Athletes

Effects of Caffeine-Taurine Co-Ingestion on Endurance Cycling Performance in High Temperature and Humidity Environments

BACKGROUND

Taurine (TAU) and caffeine (CAF), as common ergogenic aids, are known to affect exercise performance; however, the effects of their combined supplementation, particularly in high temperature and humidity environments, have not been studied.

HYPOTHESIS

The combination of TAU and CAF will have a greater effect on endurance cycle performance and improve changes in physiological indicators during exercise compared with TAU or CAF supplementation alone and placebo.

STUDY DESIGN

Single-blind crossover randomized controlled study.

LEVEL OF EVIDENCE

Level 1.

METHODS

Twelve university students majoring in physical education volunteered to receive 4 different supplement ingestions: (1) placebo (maltodextrin), (2) TAU, (3) CAF, (4) TAU + CAF. After a 7-day washout period, participants completed a time to exhaustion (TTE) test in the heat (35°C, 65% relative humidity).

RESULTS

All experimental groups improved TTE compared with the placebo group. Peak and mean power of countermovement jump were significantly higher in the CAF group compared with the placebo group before the exhaustion exercise (P = 0.02, d = 1.2 and P = 0.04, d = 1.1, respectively). Blood lactate was significantly lower after the exhaustion test in the TAU group compared with the CAF (P < 0.01, d = 0.8) and TAU + CAF (P < 0.01, d = 0.7) groups. Core temperature in the TAU group was significantly reduced in the placebo group later in the exhaustion test (P < 0.01, d = 1.9).

CONCLUSION

In high temperature and humidity environments, acute TAU, CAF, and combined supplementation all improved TTE and did not affect recovery from lower limb neuromuscular fatigue compared with placebo, with TAU having the best effect. Combined supplementation failed to exhibit superimposed performance.

CLINICAL RELEVANCE

The results provide suggestions for the effects of TAU, CAF, and their combined intake on exercise performance in high temperature and humidity environments.

Exertional Heat Illness-From Identifying Heat Rash to Treating Heat Stroke

Heat-related illness commonly affects adolescent patients, especially as summer approaches and global temperature extremes worsen. Basic counseling on sunburn prevention can decrease the risk for future malignancies, and rapidly preventing, identifying, and treating heat stroke can prevent severe morbidity and mortality. This article will review the epidemiology of exertional heat-related illness and the variations in presentations and pathology, from heat rash and sunburn to heat exhaustion and heat stroke. By the end of this review clinicians should be able to identify and treat different heat-related illnesses in adolescents and potentially save a life. [Pediatr Ann. 2024;53(1):e17-e21.].

Heatwaves and human sleep: Stress response versus adaptation

The World Meteorological Organization considers a heatwave as "a period of statistically unusual hot weather persisting for a number of days and nights". Accompanying the ongoing global climate change, sharp heatwave bouts occur worldwide, growing in frequency and intensity, and beginning earlier in the season. Heatwaves exacerbate the risk of heat-related illnesses, hence human morbidity and mortality, particularly in vulnerable elderly and children. Heat-related illnesses present a continuum from normothermic (prickly heat, heat edema, heat cramps, heat tetany) to hyperthermic syndromes (from heat syncope and heat exhaustion to lethal heat stroke). Heat stroke may occur through passive heating and/or exertional exercise. "Normal sleep", such as observed in temperate conditions, is altered during heatwaves. Brisk excessive heat bouts shorten and fragment human sleep. Particularly, deep N3 sleep (formerly slow-wave sleep) and REM sleep are depleted, such as in other stressful situations. The resultant sleep loss is deleterious to cognitive performance, emotional brain function, behavior, and susceptibility to chronic health conditions and infectious diseases. Our group has previously demonstrated that sleep constitutes an adaptive mechanism during climatic heat acclimatization. In parallel, artificial heat acclimation procedures have been proposed in sports and military activities, and for the elderly. Other preventive actions should be considered, such as education and urban heat island cooling (vegetation, white paint), thus avoiding energy-hungry air conditioning.

The Effect of Pre-Exercise Hyperhydration on Exercise Performance, Physiological Outcomes and Gastrointestinal Symptoms: A Systematic Review

BACKGROUND

Fluid loss during prolonged exercise in hot conditions poses thermoregulatory and cardiovascular challenges for athletes that can lead to impaired performance. Pre-exercise hyperhydration using nutritional aids is a strategy that may prevent or delay the adverse effects of dehydration and attenuate the impact of heat stress on exercise performance.

OBJECTIVES

The aim of this systematic review was to examine the current literature to determine the effect of pre-exercise hyperhydration on performance, key physiological responses and gastrointestinal symptoms.

METHODS

English language, full-text articles that compared the intervention with a baseline or placebo condition were included. An electronic search of Medline Complete, SPORTDiscus and Embase were used to identify articles with the final search conducted on 11 October 2022. Studies were assessed using the American Dietetic Association Quality Criteria Checklist.

RESULTS

Thirty-eight studies involving 403 participants (n = 361 males) were included in this review (n = 22 assessed exercise performance or capacity). Two studies reported an improvement in time-trial performance (range 5.7-11.4%), three studies reported an improvement in total work completed (kJ) (range 4-5%) and five studies reported an increase in exercise capacity (range 14.3-26.2%). During constant work rate exercise, nine studies observed a reduced mean heart rate (range 3-11 beats min-1), and eight studies reported a reduced mean core temperature (range 0.1-0.8 °C). Ten studies reported an increase in plasma volume (range 3.5-12.6%) compared with a control. Gastrointestinal symptoms were reported in 26 studies, with differences in severity potentially associated with factors within the ingestion protocol of each study (e.g. treatment, dose, ingestion rate).

CONCLUSIONS

Pre-exercise hyperhydration may improve exercise capacity during constant work rate exercise due to a reduced heart rate and core temperature, stemming from an acute increase in plasma volume. The combination of different osmotic aids (e.g. glycerol and sodium) may enhance fluid retention and this area should continue to be explored. Future research should utilise valid and reliable methods of assessing gastrointestinal symptoms. Furthermore, studies should investigate the effect of hyperhydration on different exercise modalities whilst implementing a strong level of blinding. Finally, females are vastly underrepresented, and this remains a key area of interest in this area.

An Easy-to-Use Prehospital Indicator to Determine the Severity of Suspected Heat-Related Illness: An Observational Study in the Tokyo Metropolitan Area

Rapid hospital arrival decreases mortality risk in heat-related illnesses. We investigated an easy-to-use indicator of life-threatening severity of heat-related illnesses in a community setting to enable quick hospitalization by using data extracted from prehospital transportation records of a database from 2016 that included information on the clinical severity of suspected heat-related illnesses in patients (n = 2528) upon hospital arrival. Patient-related risk factors (adjusted odds ratio, aOR [95% confidence interval, CI]) included age, vital signs, location of the patient, and illness severity, and respiratory rate (3.34 [1.80-6.22]), heart rate (2.88 [1.57-5.29]), axillary body temperature (7.79 [4.02-15.1]), and consciousness level (38.3 [5.22-281.1]) were independent risk factors for heat-related illness severity. On-site blood pressure was not an independent factor for illness severity. Heart rate > 120 beats/min, respiratory rate > 24 breaths/min, and temperature > 38.6 °C (highest areas under the receiver operating characteristic curves [95% CI]: 0.80 [0.75-0.87]; 0.73 [0.67-0.81]; and 0.83 [0.77-0.91], respectively) predicted life-threatening illness severity. Changes in the vital signs of patients with heat-related illnesses, particularly tachycardia and tachypnea, constitute sensitive, easy-to-use indicators that facilitate rapid identification of severity by laypersons and transport of patients before aggravation to a life-threatening situation.

Subjective perceived risk factors of exertional heat exhaustion-related symptoms in male collegiate athletes in Japan: a case-control study

The purpose of this study was to investigate associations between lifestyle habits, health factors, athletic activity conditions, and exertional heat exhaustion (EHE)-related symptoms among male college athletes in Japan based on a self-completed questionnaire. The paper-based questionnaires were distributed to 11 universities in Japan, and 2006 respondents completed the survey. Data of personal characteristics (age, body mass), lifestyle habits (sleep duration, use of air-conditioner while sleeping, and practice duration), perceived health factors (loss of appetite, sleep deprivation, sickness, dehydration, accumulated fatigue, and mental stress), perceived athletic activity (insufficient rest breaks, high ambient temperature, excessive humidity, strong solar radiation, lack of ambient wind, and clothing discomfort), and EHE-related symptoms (dizziness, headaches, nausea, and malaise) were collected. The association between lifestyle habits, health factors, athletic activity conditions (explanatory variables), and EHE-related symptoms (objective variables) was analyzed using the partial-proportional odds model. "Perceived dehydration" (odds ratios [ORs] 1.70-2.31, p < 0.002)," "sickness" (ORs 1.35-1.76), p < 0.001), "perceived accumulated fatigue" (ORs 1.13-1.31, p ≤ 0.001), "perceived mental stress" (ORs 1.17-1.31, p < 0.019), "lack of ambient wind" (ORs 1.12-1.19, p < 0.022), "loss of appetite" (ORs 1.16-1.23, p < 0.037), and "sleep deprivation" (ORs 1.15-1.17, p < 0.025) were positively associated with EHE-related symptoms, whereas "using an air conditioner during sleeping" (ORs 0.91, p = 0.047) during summer seasons was negatively associated. These findings suggest that athletes should be allowed to postpone or downregulate exercise intensity and/or volume based on their perceptions of dehydration, sickness, accumulated fatigue, mental stress, loss of appetite, and/or sleep deprivation in the summer to prevent heat illness.

Carotid body hyperexcitability underlies heat-induced hyperventilation in exercising humans

Physical activity is the most common source of heat strain for humans. The thermal strain of physical activity causes overbreathing (hyperventilation) and this has adverse physiological repercussions. The mechanisms underlying heat-induced hyperventilation during exercise are unknown, but recent evidence supports a primary role of carotid body hyperexcitability (increased tonic activity and sensitivity) underpinning hyperventilation in passively heated humans. In a repeated-measures crossover design, 12 healthy participants (6 female) completed two low-intensity cycling exercise conditions (25% maximal aerobic power) in randomized order, one with core temperature (T_C) kept relatively stable near thermoneutrality, and the other with progressive heat strain to +2°C T_C. To provide a complete examination of carotid body function under graded heat strain, carotid body tonic activity was assessed indirectly by transient hyperoxia, and its sensitivity estimated by responses to both isocapnic and poikilocapnic hypoxia. Carotid body tonic activity was increased by 220 ± 110% during cycling alone, and by 400 ± 290% with supplemental thermal strain to +1°C T_C, and 600 ± 290% at +2°C T_C (interaction, P = 0.0031). During exercise with heat stress at both +1°C and +2°C T_C, carotid body suppression by hyperoxia decreased ventilation below the rates observed during exercise without heat stress (P < 0.0147). Carotid body sensitivity was increased by up to 230 ± 190% with exercise alone, and by 290 ± 250% with supplemental heating to +1°C T_C and 510 ± 470% at +2°C T_C (interaction, P = 0.0012). These data indicate that the carotid body is further activated and sensitized by heat strain during exercise and this largely explains the added drive to breathe.NEW & NOTEWORTHY Physical activity is the most common way humans increase their core temperature, and excess breathing in the heat can limit heat tolerance and performance, and may increase the risk of heat-related injury. Dose-dependent increases in carotid body tonic activity and sensitivity with core heating provide compelling evidence that carotid body hyperexcitability is the primary cause of heat-induced hyperventilation during exercise.

Trends in ambulance dispatches related to heat illness from 2010 to 2019: An ecological study

Heatstroke is a serious heat-related illness that can even cause death. Heat alert systems play an important role in reducing the number of patients experiencing heat illness, as they encourage preventive actions such as the use of air conditioning, hydration, or other strategies. However, to date, the Japanese hazard classification has not considered seasonal and regional variations, despite clear differences in meteorological conditions across different regions in Japan. Moreover, several studies have reported a difference in thermoregulation between older and younger adults, implying that the hazard classification should also consider age differences. This study examined the relationship between the number of ambulance dispatches related to heat illness (ADRHI) and the Japanese heat hazard classification from 2010 to 2019, focusing on monthly and regional differences. Data from 47 prefectures during the 10-year period were collected and analyzed. ADRHI and wet bulb globe temperature (WBGT) data were collected from Japan’s Ministry of Internal Affairs and Communications and the Ministry of the Environment Heat Illness Prevention Information website, respectively. The findings showed a significant relationship between ADRHI and WBGT_max (p < 0.05, r = 0.74). ADRHI per 100,000 people showed significant differences across months. The post hoc test detected the first steep increase in ADRHI at a WBGT_max of 23°C than at 22°C in June, and at a WBGT_max of 26°C, 27°C, and 25°C in July, August, and September, respectively. Moreover, the first significant increase in ADRHI per 100,000 people at WBGT_max differed across each region, at a WBGT_max of 24°C in Hokkaido-Tohoku, 25°C in Kanto, Kansai, and Chugoku, 26°C in Chubu, 27°C in Shikoku, and 28°C in Kyushu-Okinawa. Further, Poisson regression analysis revealed that the relative risks differed across each region and month. These results imply that the hazard classification should be adjusted according to region and month in Japan.

Indicators to assess physiological heat strain – Part 1: Systematic review

In a series of three companion papers published in this Journal, we identify and validate the available thermal stress indicators (TSIs). In this first paper of the series, we conducted a systematic review (registration: INPLASY202090088) to identify all TSIs and provide reliable information regarding their use (funded by EU Horizon 2020; HEAT-SHIELD). Eight databases (PubMed, Agricultural and Environmental Science Collection, Web of Science, Scopus, Embase, Russian Science Citation Index, MEDLINE, and Google Scholar) were searched from database inception to 15 April 2020. No restrictions on language or study design were applied. Of the 879 publications identified, 232 records were considered for further analysis. This search identified 340 instruments and indicators developed between 200 BC and 2019 AD. Of these, 153 are nomograms, instruments, and/or require detailed non-meteorological information, while 187 can be mathematically calculated utilizing only meteorological data. Of these meteorology-based TSIs, 127 were developed for people who are physically active, and 61 of those are eligible for use in occupational settings. Information regarding the equation, operating range, interpretation categories, required input data, as well as a free software to calculate all 187 meteorology-based TSIs is provided. The information presented in this systematic review should be adopted by those interested in performing on-site monitoring and/or big data analytics for climate services to ensure appropriate use of the meteorology-based TSIs. Studies two and three in this series of companion papers present guidance on the application and validation of these TSIs, to guide end users of these indicators for more effective use.

Wilderness Medicine: Impacts from the Weather, Water, and World

Pediatricians play an important role in the prevention of injuries and provide families with anticipatory guidance regularly. As more families are traveling and spending time outdoors, we must be adept at providing them with knowledge and resources to set them up for success on their adventures. Prevention and preparation frequently can help limit injuries sustained in the wilderness. This article will focus specifically on injuries related to the environment (eg, cold weather injuries, heat-related illnesses) and travel location (eg, high-altitude illness, marine-related injuries, diving medicine). [Pediatr Ann. 2022;51(6):e212-217.].

Chronic prescription medication use in endurance runners: a cross-sectional study in 76,654 race entrants - SAFER XV

OBJECTIVE

To determine the prevalence of chronic prescription medication (CPM) use in distant runners (by age and sex) and to compare CPM use in 21.1 km vs. 56 km race entrants.

METHODS

A cross-sectional study of 76,654 race entrants who completed a pre-race medical screening questionnaire during race registration, which included questions on the use of CPM and CPM use in eight main categories of CPM. Prevalence (%, 95%CIs) and prevalence ratios (PR) are reported.

RESULTS

The prevalence of any CPM use was 12.5% (12.2-12.8). CPM use was higher in older age categories vs. the youngest age category (31-40 yrs vs. ≤30 yrs: PR = 1.4; 41-50 yrs vs. ≤30 yrs: PR = 2.1; >50 yrs vs. ≤30 yrs: PR = 3.4) (p < 0.0001) and females vs. males (PR = 1.1; p < 0.0001). The use of any CPM was significantly higher in 21.1 km vs. 56 km race entrants (PR = 1.2; p < 0.0001). Prevalence of CPM use in main categories was: blood pressure lowering medication (3.7%), cholesterol lowering medication (3.6%), asthma medication (3.1%), and medication to treat anxiety/depression (2.6%). The pattern of CPM in the main categories differed between 21.1 km and 56 km race entrants.

CONCLUSIONS

One in eight race entrants use CPM, with a higher prevalence of use among older race entrants, female vs. males, and 21.1 km vs. 56 km race entrants. Frequent CPMs used are blood pressure lowering medication, cholesterol lowering medication, asthma medication, and medication to treat anxiety/depression. The use of CPM medications may increase the risk of medical complications during exercise, and these data help identify subgroups of entrants that may be at higher risk for race medical encounters.

Hard Boiled: Alcohol Use as a Risk Factor for MDMA-Induced Hyperthermia: a Systematic Review

Although MDMA (ecstasy) is a relatively safe recreational drug and is currently considered for therapeutic use for the treatment of posttraumatic stress disorder (PTSD) and alcohol use disorder (AUD), recreational MDMA use occasionally elicits hyperthermia and hyponatremia, sometimes with a fatal outcome. Specific risk factors for both adverse effects are profuse sweating while vigorously dancing under unfavorable conditions such as high ambient temperatures and insufficient fluid suppletion which result in dehydration. Concomitant use of MDMA and alcohol is highly prevalent, but adds to the existing risk, because alcohol facilitates the emergence of MDMA-induced adverse events, like hyperthermia, dehydration, and hyponatremia. Because of potential health-related consequences of concomitant use of MDMA and alcohol, it is important to identify the mechanisms of the interactions between alcohol and MDMA. This review summarizes the main drivers of MDMA-induced hyperthermia, dehydration, and hyponatremia and the role of concomitant alcohol use. It is shown that alcohol use has a profound negative impact by its interaction with most of these drivers, including poikilothermia, exposure to high ambient temperatures, heavy exercise (vigorous dancing), vasoconstriction, dehydration, and delayed initiation of sweating and diuresis. It is concluded that recreational and clinical MDMA-users should refrain from concomitant drinking of alcoholic beverages to reduce the risk for adverse health incidents when using MDMA.

Estimating the magnitude and risk associated with heat exposure among Ghanaian mining workers

Many occupational settings located outdoors in direct sun, such as open cut mining, pose a health, safety, and productivity risk to workers because of their increased exposure to heat. This issue is exacerbated by climate change effects, the physical nature of the work, the requirement to work extended shifts and the need to wear protective clothing which restricts evaporative cooling. Though Ghana has a rapidly expanding mining sector with a large workforce, there appears to be no study that has assessed the magnitude and risk of heat exposure on mining workers and its potential impact on this workforce. Questionnaires and temperature data loggers were used to assess the risk and extent of heat exposure in the working and living environments of Ghanaian miners. The variation in heat exposure risk factors across workers' gender, education level, workload, work hours, physical work exertion and proximity to heat sources is significant (p<0.05). Mining workers are vulnerable to the hazards of heat exposure which can endanger their health and safety, productive capacity, social well-being, adaptive capacity and resilience. An evaluation of indoor and outdoor Wet Bulb Globe Temperature (WBGT) in the working and living environment showed that mining workers can be exposed to relatively high thermal load, thus raising their heat stress risk. Adequate adaptation policies and heat exposure management for workers are imperative to reduce heat stress risk, and improve productive capacity and the social health of mining workers.

Enhanced intestinal permeability and intestinal co-morbidities in heat strain: A review and case for autodigestion

Enhanced intestinal permeability is a pervasive issue in modern medicine, with implications demonstrably associated with significant health consequences such as sepsis, multiorgan failure, and death. Key issues involve the trigger mechanisms that could compromise intestinal integrity and increase local permeability allowing the passage of larger, potentially dangerous molecules. Heat stress, whether exertional or environmental, may modulate intestinal permeability and begs interesting questions in the context of global climate change, increasing population vulnerabilities, and public health. Emerging evidence indicates that intestinal leakage of digestive enzymes and associated cell dysfunctions--a process referred to as autodigestion--may play a critical role in systemic physiological damage within the body. This increased permeability is exacerbated in the presence of elevated core temperatures. We employed Latent Dirichlet Allocation (LDA) topic modeling methods to analyze the relationship between heat stress and the nascent theory of autodigestion in a systematic, quantifiable, and unbiased manner. From a corpus of 11,233 scientific articles across four relevant scientific journals (Gut, Shock, Temperature, Gastroenterology), it was found that over 1,000 documents expressed a relationship between intestine, enhanced permeability, core temperature, and heat stress. The association has grown stronger in recent years, as heat stress and potential autodigestion are investigated in tandem, yet still by a limited number of specific research studies. Such findings justify the design of future studies to critically test novel interventions against digestive enzymes permeating the intestinal tract, especially the small intestine.

Thermoregulation is not impaired in breast cancer survivors during moderate-intensity exercise performed in warm and hot environments

This study aimed to assess how female breast cancer survivors (BCS) respond physiologically, hematologically, and perceptually to exercise under heat stress compared to females with no history of breast cancer (CON). Twenty-one females (9 BCS and 12 CON [age; 54 ± 7 years, stature; 167 ± 6 cm, body mass; 68.1 ± 7.62 kg, and body fat; 30.9 ± 3.8%]) completed a warm (25℃, 50% relative humidity, RH) and hot (35℃, 50%RH) trial in a repeated-measures crossover design. Trials consisted of 30 min of rest, 30 min of walking at 4 metabolic equivalents, and a 6-minute walk test (6MWT). Physiological measurements (core temperature (Tre ), skin temperature (Tskin ), heart rate (HR), and sweat analysis) and perceptual rating scales (ratings of perceived exertion, thermal sensation [whole body and localized], and thermal comfort) were taken at 5- and 10-min intervals throughout, respectively. Venous blood samples were taken before and after to assess; IL-6, IL-10, CRP, IFN-γ, and TGF-β1 . All physiological markers were higher during the 35 versus 25℃ trial; Tre (~0.25℃, p = 0.002), Tskin (~3.8℃, p < 0.001), HR (~12 beats·min-1 , p = 0.023), and whole-body sweat rate (~0.4 L·hr-1 , p < 0.001), with no difference observed between groups in either condition (p > 0.05). Both groups covered a greater 6MWT distance in 25 versus 35℃ (by ~200 m; p = 0.003). Nevertheless, the control group covered more distance than BCS, regardless of environmental temperature (by ~400 m, p = 0.03). Thermoregulation was not disadvantaged in BCS compared to controls during moderate-intensity exercise under heat stress. However, self-paced exercise performance was reduced for BCS regardless of environmental temperature.

Bio-inspired fractal textile device for rapid sweat collection and monitoring

In this study, a new design concept in sweat collection was developed to achieve rapid and intact sweat sampling for analytical purposes. Textiles with fast water wicking properties were first selected and laser engraved into tree-like bifurcating channels for sweat collection. The fractal framework of the bifurcating textile channels was theoretically derived to minimize the flow resistance for fast sweat absorption. The optimized collector with designed fractal geometry exhibited thorough coverage of emerging droplets without overflow. Great collection efficiency was achieved with a short induction time (<1 minute after perspiration begins) and a maximum sweat collection flux up to 4.0 μL cm-2 min-1 without leakage. After being combined with printed sensors and microchips, the assembled sweat collection/sensing device can simultaneously provide measurements of salt concentration and sweat rate for wireless hydration state monitoring. The collection/sensing system also exhibited fast response times to abrupt changes in sweat rates or concentrations and thus can be used to detect instant physical conditions in exercise. Finally, field tests were performed to demonstrate the reliability and practicality of the device in real-time sweat monitoring under vigorous activities.

Noninvasive Estimation of Hydration Status in Athletes Using Wearable Sensors and a Data-Driven Approach Based on Orthostatic Changes

Dehydration beyond 2% bodyweight loss should be monitored to reduce the risk of heat-related injuries during exercise. However, assessments of hydration in athletic settings can be limited in their accuracy and accessibility. In this study, we sought to develop a data-driven noninvasive approach to measure hydration status, leveraging wearable sensors and normal orthostatic movements. Twenty participants (10 males, 25.0 ± 6.6 years; 10 females, 27.8 ± 4.3 years) completed two exercise sessions in a heated environment: one session was completed without fluid replacement. Before and after exercise, participants performed 12 postural movements that varied in length (up to 2 min). Logistic regression models were trained to estimate dehydration status given their heart rate responses to these postural movements. The area under the receiver operating characteristic curve (AUROC) was used to parameterize the model's discriminative ability. Models achieved an AUROC of 0.79 (IQR: 0.75, 0.91) when discriminating 2% bodyweight loss. The AUROC for the longer supine-to-stand postural movements and shorter toe-touches were similar (0.89, IQR: 0.89, 1.00). Shorter orthostatic tests achieved similar accuracy to clinical tests. The findings suggest that data from wearable sensors can be used to accurately estimate mild dehydration in athletes. In practice, this method may provide an additional measurement for early intervention of severe dehydration.

An Ice Vest, but Not Single-Hand Cooling, Is Effective at Reducing Thermo-Physiological Strain During Exercise Recovery in the Heat

Sports limit the length of breaks between halves or periods, placing substantial time constraints on cooling effectiveness. This study investigated the effect of active cooling during both time-limited and prolonged post-exercise recovery in the heat. Ten recreationally-active adults (VO2peak 43.6 ± 7.5 ml·kg-1·min-1) were exposed to thermally-challenging conditions (36°C air temperature, 45% RH) while passively seated for 30 min, cycling for 60 min at 51% VO2peak, and during a seated recovery for 60 min that was broken into two epochs: first 15 min (REC0-15) and total 60 min (REC0-60). Three different cooling techniques were implemented during independent recovery trials: (a) negative-pressure single hand-cooling (~17°C); (b) ice vest; and (c) non-cooling control. Change in rectal temperature (T re), mean skin temperature (T ¯ sk ), heart rate (HR), and thermal sensation (TS), as well as mean body temperature (T ¯ b ), and heat storage (S) were calculated for exercise, REC0-15 and REC0-60. During REC0-15, HR was lowered more with the ice vest (-9 [-15 to -3] bts·min-1, p = 0.002) and single hand-cooling (-7 [-13 to -1] bts·min-1, p = 0.021) compared to a non-cooling control. The ice vest caused a greater change inT ¯ sk compared to no cooling (-1.07 [-2.00 to -0.13]°C, p = 0.021) and single-hand cooling (-1.07 [-2.01 to -0.14]°C, p = 0.020), as well as a greater change in S compared to no cooling (-84 [-132 to -37] W, p < 0.0001) and single-hand cooling (-74 [-125 to -24] W, p = 0.002). Across REC0-60, changes inT ¯ b (-0.38 [-0.69 to -0.07]°C, p = 0.012) andT ¯ sk (-1.62 [-2.56 to -0.68]°C, p < 0.0001) were greater with ice vest compared to no cooling. Furthermore, changes in inT ¯ b (-0.39 [-0.70 to -0.08]°C, p = 0.010) andT ¯ sk (-1.68 [-2.61 to -0.74]°C, p < 0.0001) were greater with the ice vest compared to single-hand cooling. Using an ice vest during time-limited and prolonged recovery in the heat aided in a more effective reduction in thermo-physiological strain compared to both passive cooling as well as a single-hand cooling device.

Acute associations between heatwaves and preterm and early-term birth in 50 US metropolitan areas: a matched case-control study

BACKGROUND

The effect of heatwaves on adverse birth outcomes is not well understood and may vary by how heatwaves are defined. The study aims to examine acute associations between various heatwave definitions and preterm and early-term birth.

METHODS

Using national vital records from 50 metropolitan statistical areas (MSAs) between 1982 and 1988, singleton preterm (< 37 weeks) and early-term births (37-38 weeks) were matched (1:1) to controls who completed at least 37 weeks or 39 weeks of gestation, respectively. Matching variables were MSA, maternal race, and maternal education. Sixty heatwave definitions including binary indicators for exposure to sustained heat, number of high heat days, and measures of heat intensity (the average degrees over the threshold in the past 7 days) based on the 97.5th percentile of MSA-specific temperature metrics, or the 85th percentile of positive excessive heat factor (EHF) were created. Odds ratios (OR) for heatwave exposures in the week preceding birth (or corresponding gestational week for controls) were estimated using conditional logistic regression adjusting for maternal age, marital status, and seasonality. Effect modification by maternal education, age, race/ethnicity, child sex, and region was assessed.

RESULTS

There were 615,329 preterm and 1,005,576 early-term case-control pairs in the analyses. For most definitions, exposure to heatwaves in the week before delivery was consistently associated with increased odds of early-term birth. Exposure to more high heat days and more degrees above the threshold yielded higher magnitude ORs. For exposure to 3 or more days over the 97.5th percentile of mean temperature in the past week compared to zero days, the OR was 1.027 for early-term birth (95%CI: 1.014, 1.039). Although we generally found null associations when assessing various heatwave definitions and preterm birth, ORs for both preterm and early-term birth were greater in magnitude among Hispanic and non-Hispanic black mothers.

CONCLUSION

Although associations varied across metrics and heatwave definitions, heatwaves were more consistently associated with early-term birth than with preterm birth. This study's findings may have implications for prevention programs targeting vulnerable subgroups as climate change progresses.

The influence of acclimatization on stress hormone concentration in serum during heat stress

This study was aimed to examine the influence of acclimatization on the change of concentration of stress hormones in men's serum exposed to heat stress during physical training. The study included a total of 40 men, aged 19-21 years, divided randomly into four groups: CTRL group: control, exposed to the Exercise Tolerance Testing in comfortable conditions; O group: exposed to Exercise Tolerance Testing in a warm environment; P group: exposed to passive acclimation to heat for 10 days, followed by Exercise Tolerance Testing in a warm environment; A group: exposed to active acclimation to heat for 10 days, followed by Exercise Tolerance Testing in a warm environment. All participants were tested for thermoregulation and acclimatization, skin and tympanic temperature, heart rate (HR), hormonal status and sweating. The mean skin temperature was the lowest in the control group of subjects exposed to physical exertion under comfortable conditions, and at each point of measurement it was statistically significantly different from that of the other study groups (p < 0.001). Sweating intensity was statistically significantly the lowest in the CTRL group (0.32 ± 0.04 l/m²/h; p < 0.001), compared to all other groups. Cortisol was significantly altered in O group (632.2 ± 92.3; 467.2 ± 89.7), testosterone levels were significantly altered in P (19.2 ± 9.3; 16.4 ± 7.3) and in A groups (22.1 ± 12.4; 14.9 ± 9.9), while prolactin was changed in O (392.1 ± 51.3; 181.4 ± 42.3), P (595.1 ± 191.1; 191.2 ± 52.5), and A group (407.4 ± 189.3; 173.4 ± 43.9) after the experimental period. The impact of acclimatization on hormonal indicators emphasizes its importance in the response of the endocrine system of soldiers to perform military activities in warm climates.

Cardiovascular Effects of Compression Garments During Uncompensable Heat Stress

ABSTRACT

Bautz, J, Hostler, D, Khorana, P, and Suyama, J. Cardiovascular effects of compression garments during uncompensable heat stress. J Strength Cond Res 35(4): 1058-1065, 2021-This study examined the potential hemodynamic benefits of wearing lower extremity compression garments (CGs) beneath thermal protective clothing (TPC) worn by wildland firefighters, while exercising in a heated environment. Using in a counterbalanced design, 10 male subjects ([mean ± SD] age 27 ± 6 years, height 1.78 ± 0.09 m, body mass 74.8 ± 7.0 kg, body fat 10.6 ± 4.2%, and V̇o2max 57.8 ± 9.3 ml·kg-1·min-1) completed control (no CG) and experimental (CG) conditions in randomly assigned order. Protocols were separated by a minimum of 3 days. Subjects exercised for 90 minutes (three, 30-minute segments) on a treadmill while wearing wilderness firefighter TPC and helmet in a heated room. Venous blood was drawn before and after exercise to measure hemoglobin (Hgb), hematocrit (Hct), serum osmolarity (OSM), and serum creatine phosphokinase (CPK). Vital signs and perceptual measures of exertion and thermal comfort were recorded during the protocol. Data were analyzed by the paired t-test. There were no differences in the change in heart rate (84 ± 27 vs. 85 ± 14 b·min-1, p = 0.9), core temperature rise (1.8 ± 0.6 vs. 1.9 ± 0.5° C, p = 0.39), or body mass lost (-1.72 ± 0.78 vs. -1.77 ± 0.58 kg, p = 0.7) between the conditions. There were no differences in the change in Hgb (0.49 ± 0.66 vs. 0.33 ± 1.11 g·dl-1, p = 0.7), Hct (1.22 ± 1.92 vs. 1.11 ± 3.62%, p = 0.9), OSM (1.67 ± 6.34 vs. 6.22 ± 11.39 mOsm·kg-1, p = 0.3), or CPK (22.2 ± 30.2 vs. 29.8 ± 19.4 IU·L-1, p = 0.5). Total distance walked (3.9 ± 0.5 vs. 4.0 ± 0.5 miles, p = 0.2), exercise interval (88.6 ± 3.5 vs. 88.4 ± 3.6 minutes, p = 0.8), and perceptual measures were similar between conditions. Compression garments worn beneath TPC did not acutely alter the physiologic response to exertion in TPC. With greater use in the general public related to endurance activities, the data neither encourage nor discourage CG use during uncompensable heat stress.

Fundamental Concepts of Human Thermoregulation and Adaptation to Heat: A Review in the Context of Global Warming

The international community has recognized global warming as an impending catastrophe that poses significant threat to life on earth. In response, the signatories of the Paris Agreement (2015) have committed to limit the increase in global mean temperature to <1.5 °C from pre-industry period, which is defined as 1850–1890. Considering that the protection of human life is a central focus in the Paris Agreement, the naturally endowed properties of the human body to protect itself from environmental extremes should form the core of an integrated and multifaceted solution against global warming. Scholars believe that heat and thermoregulation played important roles in the evolution of life and continue to be a central mechanism that allows humans to explore, labor and live in extreme conditions. However, the international effort against global warming has focused primarily on protecting the environment and on the reduction of greenhouse gases by changing human behavior, industrial practices and government policies, with limited consideration given to the nature and design of the human thermoregulatory system. Global warming is projected to challenge the limits of human thermoregulation, which can be enhanced by complementing innate human thermo-plasticity with the appropriate behavioral changes and technological innovations. Therefore, the primary aim of this review is to discuss the fundamental concepts and physiology of human thermoregulation as the underlying bases for human adaptation to global warming. Potential strategies to extend human tolerance against environmental heat through behavioral adaptations and technological innovations will also be discussed. An important behavioral adaptation postulated by this review is that sleep/wake cycles would gravitate towards a sub-nocturnal pattern, especially for outdoor activities, to avoid the heat in the day. Technologically, the current concept of air conditioning the space in the room would likely steer towards the concept of targeted body surface cooling. The current review was conducted using materials that were derived from PubMed search engine and the personal library of the author. The PubMed search was conducted using combinations of keywords that are related to the theme and topics in the respective sections of the review. The final set of articles selected were considered “state of the art,” based on their contributions to the strength of scientific evidence and novelty in the domain knowledge on human thermoregulation and global warming.

Health Risks and Interventions in Exertional Heat Stress

BACKGROUND

With climate change, heat waves are expected to become more frequent in the near future. Already, on average more than 25 000 "heat deaths" are estimated to occur in Europe every year. However, heat stress and heat illnesses arise not just when ambient temperatures are high. Physical exertion increases heat production within the organism many times over; if not enough heat is lost, there is a risk of exertional heat stress. This review article discusses contributing factors, at-risk groups, and the diagnosis and treatment of heat illnesses.

METHODS

A selective literature search was carried out on PubMed. Current guidelines and expert recommendations were also included.

RESULTS

Apart from muscular heat production (>70% of converted energy), there are other factors that singly or in combination can give rise to heat stress: clothing, climate/acclimatization, and individual factors. Through its insulating properties, clothing reduces the evaporation of sweat (the most effective physiological cooling mechanism). A sudden heat wave, or changing the climate zone (as with air travel), increases the risk of a heat-related health event. Overweight, low fitness level, acute infections, illness, dehydration, and other factors also reduce heat tolerance. In addition to children, older people are particularly at risk because of their reduced physiological adaptability, (multi-)morbidity, and intake of prescription drugs. A heat illness can progress suddenly to life-threatening heat stroke. Successful treatment depends on rapid diagnosis and cooling the body down as quickly as possible. The aim is to reduce core body temperature to <40 °C within 30 minutes.

CONCLUSION

Immediately effective cooling interventions are the only causal treatment for heat stroke. Time once lost cannot be made up. Prevention (acclimatization, reduced exposure, etc.) and terminating the heat stress in good time (e.g., stopping work) are better than any cure.

Diverse Effects of Thermal Conditions on Performance of Marathon Runners

Heat exposure affects human performance in many ways. Both physiological (i.e., glycogen sparing, oxygen uptake, thermoregulation) and biomechanical mechanisms (i.e., contact time, knee flexion, muscle activity) are affected, hence reducing performance. However, the exposure affects persons differently. Not all athletes necessarily experience an identical thermal condition similarly, and this point has been overlooked to date. We analyzed endurance performances of the top 1000 runners for every year during the last 12 New York City Marathons. Thermal conditions were estimated with wet-bulb globe temperature (WBGT) and universal thermal climate index (UTCI). Under identical thermal exposure, the fastest runners experienced a larger decline in performance than the slower ones. The empirical evidence offered here not only shows that thermal conditions affect runners differently, but also that some groups might consistently suffer more than others. Further research may inspect other factors that could be affected by thermal conditions, as pacing and race strategy.

Heat related illnesses. Review of an ongoing challenge

Climate change is the most challenging natural calamity of chronic nature that presents intense episodes of heat waves, and events. Effects of heat waves and increasing average temperature on heat-related illnesses (HRIs) demand a review of existing preventive and treatment strategies to direct future research. Heat-related illnesses are presented as minor to severe life-threatening conditions. Despite the understanding of the pathophysiology of HRI, pharmacological interventions are limited. Prevention is the best strategy against HRI. There is a dearth of epidemiological studies that reviewed the effect of pharmacological interventions on mortality, and there remains a need to identify critical key components other than inflammatory modulators, which can be targeted to decrease HRI.

Wearable Battery-Free Perspiration Analyzing Sites Based on Sweat Flowing on ZnO Nanoarrays

We fabricated wearable perspiration analyzing sites for actively monitoring physiological status during exercises without any batteries or other power supply. The device mainly consists of ZnO nanowire (NW) arrays and flexible polydimethylsiloxane substrate. Sweat on the skin can flow into the flow channels of the device through capillary action and flow along the channels to ZnO NWs. The sweat flowing on the NWs (with lactate oxidase modification) can output a DC electrical signal, and the outputting voltage is dependent on the lactate concentration in the sweat as the biosensing signal. ZnO NWs generate electric double layer (EDL) in sweat, which causes a potential difference between the upper and lower ends (hydrovoltaic effect). The product of the enzymatic reaction can adjust the EDL and influence the output. This device can be integrated with wireless transmitter and may have potential application in constructing sports big data. This work promotes the development of next generation of biosensors and expands the scope of self-powered physiological monitoring system.

A retrospective analysis to determine if exercise training-induced thermoregulatory adaptations are mediated by increased fitness or heat acclimation

NEW FINDINGS

What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity V ̇ O 2 max or is it the partial heat acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low V ̇ O 2 max displayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, not V ̇ O 2 max per se, that mediates thermoregulatory improvements during uncompensable heat stress.

ABSTRACT

It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption V ̇ O 2 max , independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise-induced heat stress during regular aerobic training. The present analysis sought to determine if V ̇ O 2 max independently influences thermoregulatory sweating, maximum skin wettedness (ω_max ) and the change in rectal temperature (ΔT_re ) during 60 min of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% relative humidity) at a fixed rate of heat production per unit mass (6 W kg^-1 ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n = 7; V ̇ O 2 max : 41.7 ± 9.4 ml kg^-1  min^-1 ), aerobically fit (F; n = 7; V ̇ O 2 max : 55.6 ± 4.3 ml kg^-1  min^-1 ; P < 0.01) and aerobically unfit (n = 8) individuals, before (pre; V ̇ O 2 max : 45.8 ± 11.6 ml kg^-1  min^-1 ) and after (post; V ̇ O 2 max : 52.0 ± 11.1 ml kg^-1  min^-1 ; P < 0.001) an 8-week training intervention. ω_max was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ω_max was greater post- (0.84 ± 0.08) compared to pre- (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper-back) was greater post- (1.24 ± 0.20 mg cm^-2  min^-1 ) compared to pre- (1.04 ± 0.25 mg cm^-2  min^-1 , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg cm^-2  min^-1 , P = 0.90) and F (1.02 ± 0.30 mg cm^-2  min^-1 ). The ΔT_re at 60 min of exercise was greater pre- (1.13 ± 0.16°C, P < 0.01) compared to post- (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, not V ̇ O 2 max per se, confers an increased ω_max , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.

Wearable Sensor System to Monitor Physical Activity and the Physiological Effects of Heat Exposure

Mobile health monitoring via non-invasive wearable sensors is poised to advance telehealth for older adults and other vulnerable populations. Extreme heat and other environmental conditions raise serious health challenges that warrant monitoring of real-time physiological data as people go about their normal activities. Mobile systems could be beneficial for many communities, including elite athletes, military special forces, and at-home geriatric monitoring. While some commercial monitors exist, they are bulky, require reconfiguration, and do not fit seamlessly as a simple wearable device. We designed, prototyped and tested an integrated sensor platform that records heart rate, oxygen saturation, physical activity levels, skin temperature, and galvanic skin response. The device uses a small microcontroller to integrate the measurements and store data directly on the device for up to 48+ h. continuously. The device was compared to clinical standards for calibration and performance benchmarking. We found that our system compared favorably with clinical measures, such as fingertip pulse oximetry and infrared thermometry, with high accuracy and correlation. Our novel platform would facilitate an individualized approach to care, particularly those whose access to healthcare facilities is limited. The platform also can be used as a research tool to study physiological responses to a variety of environmental conditions, such as extreme heat, and can be customized to incorporate new sensors to explore other lines of inquiry.

Impacts of weather, work rate, hydration, and clothing in heat-related illness in California farmworkers

BACKGROUND

The primary aim of this study was to investigate the effects of work rate, hydration status, and clothing on core body temperature (CBT) on California farmworkers.

METHODS

Two hundred and eighty-seven farmworkers were recruited in Summer 2015, with 259 participants having sufficient data for analysis. We collected CBT, ambient temperature, work rate, body weight loss, and clothing worn by each participant throughout the work day and demographic data from a questionnaire.

RESULTS

Multiple regression with CBT as the outcome was used to determine the adjusted associations between CBT, environmental heat load, and worker characteristics. The multivariate regression model showed statistically significant associations of CBT with work rate (β = .006, 95% CI [0.004, 0.009]) and wet-bulb globe temperature (β = .03, 95% CI [0.017, 0.05]).

CONCLUSION

Results suggest that among our population workload is the primary modifiable risk factor for heat-related illness. As expected, the ambient temperature was also associated with higher risk.

Women Firefighters' Health and Well-Being: An International Survey

OBJECTIVES

This study aimed to identify specific health and well-being issues that women firefighters may experience as part of their daily working practices. Issues identified from this under-represented population can drive future research, education, and strategy to guide safety and health practices.

METHODS

A total of 840 women firefighters from 14 separate countries (255 United Kingdom and Ireland, 320 North America, 177 Australasia, and 88 mainland Europe) completed the survey over a 4-month period. Questions related to general health and well-being and role-specific health concerns, gender-related issues, and available exercise facilities.

RESULTS

Women firefighters in North America reported a higher prevalence of lower back (49%) and lower limb (51%) injuries than all other groups. North American respondents reported more heat illnesses (45%) than respondents from other places (36%). Although many participants did not respond, of those who did, 39% thought the menstrual cycle (199/512) or menopause (55/151) affected their work, and 36% were concerned for their ability to meet future job demands. Sixteen percent felt confident they could complete the role after 60 years of age. Women firefighters identified a lack of strength and conditioning support (50%) or lack of gym access (21%). There appears to be poor availability of female-specific personal protective equipment, with availability greatest in the United Kingdom (66%) compared with the sample as a whole (42%).

CONCLUSIONS

There is a need for female-specific strength and conditioning support and facilities to decrease injury and illness risk and improve longevity. Research and education into gynecological issues, heat exposure, and their effects on women firefighters' fertility and cancer risk is required.

Protective measures of patients with cardiovascular diseases from exposure to heat waves: medicated and non-medicated

In conditions of climate warming with an increase in heat waves associated with an increase in cardiovascular morbidity and mortality, the particular interest is the effect of cardiovascular drugs on adaptation to high temperatures. The review reflects the results of European and domestic studies on the safety of therapy during long and short heat waves. Recommendations for the correction of therapy during this period are given. Self-control of blood pressure (SCAD) is a mandatory component of the therapy of arterial hypertension during heat waves. With the development of clinically significant hypotension, a reduction in the dose of antihypertensive drugs is necessary. It is recommended to start with a dose reduction and/or withdrawal of diuretics and nitrates. Not recommended the complete abolition of antihypertensive therapy because of the risk of hypertensive crises, characteristic of abnormal heat, as well as due to the increase in blood pressure when the weather changes and the temperature drops. With increasing blood pressure during heat waves, it is recommended to give preference to calcium channel antagonists, angiotensin converting enzyme inhibitors (ACE inhibitors) and selective beta-blockers. It is necessary to inform patients about the additional protective effect of statins in order to increase adherence to therapy. Patients taking diuretics require individual daily monitoring of fluid intake and body weight. An overview of recommendations on sanogenic behavior during heat waves is given. Details are considered rules for the use of air conditioning, methods of diagnosis of dehydration and drinking mode Keywords: heat waves, cardiovascular complications, preventive measures.

Canine environmental hyperthermia: a case series

Cases of hyperthermia caused by exposure to high environmental temperature are not uncommonly encountered in dogs. The circumstances surrounding the exposure to high environmental temperature may be accidental or intentional; thus highlighting the importance to perform a forensic autopsy. This report documents three cases of canine environmentally induced hyperthermia and all dogs in this report died less than 6 hr after exposure to the high environmental temperatures. The most commonly observed macroscopic findings included cutaneous petechial and ecchymotic hemorrhage, pulmonary edema and congestion, and epicardial and endocardial hemorrhage. Microscopically, there was systemic vascular congestion and hemorrhage, fibrin thrombi formation, and occasional enterocyte and/or renal tubular necrosis. The findings from all cases were consistent with hyperthermia induced disseminated intravascular coagulation.

Reliability of a wearable sweat rate monitor and routine sweat analysis techniques under heat stress in females

INTRODUCTION

The aim of the study was to evaluate the reliability of five different sweat analysis techniques which measure; whole body sweat rate [WBSR], local sweat rate [LSR] (via technical absorbent [TA] method and KuduSmart^® monitor), sweat conductivity [SC] and sweat gland activation [SGA] in a female population when exercising moderately under heat stress.

METHODS

Fourteen females (age; 26 ± 7 years, body mass; 66.5 ± 7.6 kg, height; 167.1 ± 6.4 cm) completed a preliminary threshold walking test (to determine exercise intensity) and two main trials, separated by 2 days. Main trials consisted of 30-min seated rest in the environmental chamber (35 °C, 50% relative humidity) in an upper body sauna-suit, before its removal, and walking at a moderate intensity (4 metabolic equivalents) for 30-min (speeds ranged from 4.8 to 6.5 km h^-1). WBSR was measured via nude mass pre and post exercise. The TA and Tegaderm patches (for sweat sodium chloride) were placed on the back, forearm and chest for the entire 60-min, replicated for all participants for both trials. SGA was assessed following the 60-min trial and the KuduSmart® monitor was placed on the left arm for the 30-min of exercise.

RESULTS

WBSR, LSR methods and SC demonstrated no difference between trials (p > 0.05), good agreement (within limits), strong correlations (r ≥ 0.88) and low typical error of measurements [TEM] (< 0.04 L min^-1, 0.13 mg min^-1 cm^-2 and 8 mmol L^-1, respectively). SGA method showed moderate intra-class correlation (r = 0.80), with high TEM (5 glands) and large limits of agreement.

CONCLUSION

Sudomotor function is reliable, as demonstrated by good reliability, small TEM and strong correlations. The use of these sweat techniques is appropriate and practical in females who are exercising at moderate intensity under heat stress, and so, may aid future interventions. SGA shows larger variation and should be used with caution.

Core Temperature Responses in Elite Cricket Players during Australian Summer Conditions

This study aimed to observe core temperature responses in elite cricket players under match conditions during the summer in Australia. Thirty-eight Australian male cricketers ingested capsule temperature sensors during six four-day first-class matches between February 2016 and March 2017. Core temperature (Tc) was recorded during breaks in play. Batters showed an increase in Tc related to time spent batting of approximately 1 °C per two hours of play (p < 0.001). Increases in rate of perceived exertion (RPE) in batters correlated with smaller elevations in Tc (0.2 °C per one unit of elevation in RPE) (p < 0.001). Significant, but clinically trivial, increases in Tc of batters were found related to the day of play, wet bulb globe temperature (WBGT), air temperature, and humidity. A trivial increase in Tc (p < 0.001) was associated with time in the field and RPE when fielding. There was no association between Tc and WBGT, air temperature, humidity, or day of play in fielders. This study demonstrates that batters have greater rises in Tc than other cricket participants, and may have an increased risk of exertional heat illness, despite exposure to similar environmental conditions.

Does Cold Water or Ice Slurry Ingestion During Exercise Elicit a Net Body Cooling Effect in the Heat?

Cold water or ice slurry ingestion during exercise seems to be an effective and practical means to improve endurance exercise performance in the heat. However, transient reductions in sweating appear to decrease the potential for evaporative heat loss from the skin by a magnitude that at least negates the additional internal heat loss as a cold ingested fluid warms up to equilibrate with body temperature; thus explaining equivalent core temperatures during exercise at a fixed heat production irrespective of the ingested fluid temperature. Internal heat transfer with cold fluid/ice is always 100% efficient; therefore, when a decrement occurs in the efficiency that sweat evaporates from the skin surface (i.e. sweating efficiency), a net cooling effect should begin to develop. Using established relationships between activity, climate and sweating efficiency, the boundary conditions beyond which cold ingested fluids are beneficial in terms of increasing net heat loss can be calculated. These conditions are warmer and more humid for cycling relative to running by virtue of the greater skin surface airflow, which promotes evaporation, for a given metabolic heat production and thus sweat rate. Within these boundary conditions, athletes should ingest fluids at the temperature they find most palatable, which likely varies from athlete to athlete, and therefore best maintain hydration status. The cooling benefits of cold fluid/ice ingestion during exercise are likely disproportionately greater for athletes with physiological disruptions to sweating, such as those with a spinal cord injury or burn injuries, as their capacity for skin surface evaporative heat loss is much lower; however, more research examining these groups is needed.

Heat Sepsis Precedes Heat Toxicity in the Pathophysiology of Heat Stroke-A New Paradigm on an Ancient Disease

Heat stroke (HS) is an ancient illness dating back more than 2000 years and continues to be a health threat and to cause fatality during physical exertion, especially in military personnel, fire-fighters, athletes, and outdoor laborers. The current paradigm in the pathophysiology and prevention of HS focuses predominantly on heat as the primary trigger and driver of HS, which has not changed significantly for centuries. However, pathological and clinical reports from HS victims and research evidence from animal and human studies support the notion that heat alone does not fully explain the pathophysiology of HS and that HS may also be triggered and driven by heat- and exercise-induced endotoxemia. Exposure to heat and exercise stresses independently promote the translocation of lipopolysaccharides (LPS) from gram-negative bacteria in the gut to blood in the circulatory system. Blood concentration of LPS can increase to a threshold that triggers the systemic inflammatory response, leading to the downstream ramifications of cellular and organ damage with sepsis as the end point i.e., heat sepsis. The dual pathway model (DPM) of HS proposed that HS is triggered by two independent pathways sequentially along the core temperature continuum of >40 °C. HS is triggered by heat sepsis at Tc < 42 °C and by the heat toxicity at Tc > 42 °C, where the direct effects of heat alone can cause cellular and organ damage. Therefore, heat sepsis precedes heat toxicity in the pathophysiology of HS.

Personal risk factors associated with heat-related illness among new conscripts undergoing basic training in Thailand

Cases of exertional heat stroke have been reported every year during basic training for Royal Thai Army (RTA) conscripts. Prevention is an important strategy to reduce the incidence of heat-related illnesses. We conducted a study to identify potential indicators for the prevention and monitoring of heat-related illnesses among military conscripts undergoing basic training in Thailand. All newly inducted RTA conscripts in 5 basic training units in 5 regions in Thailand were invited to participate in a prospective cohort study from May 1 to July 9, 2013. The incidence rate of heat-related illnesses and the incidence rate ratio (IRR) based on a Poisson regression model were used to identify the independent factors associated with heat-related illnesses, daily tympanic (body) temperatures higher than 37.5°C, >3% decreases in body weight in one day, and the production of dark brown urine. Eight hundred and nine men aged 21.4 (±1.13) years were enrolled in this study. The prevalence of a body mass index (BMI) ≥30 kg/m² was 5.5%. During the study period, 53 subjects (6.6%) representing 3.41/100 person-months (95% confidence interval (CI), 2.55–4.23) developed heat-related illnesses (excluding heat rash), and no subjects experienced heat stroke. The incidence rates of a daily tympanic temperature >37.5°C at least once, body weight loss of >3% per day, and the production of dark brown urine at least once were 8.27/100 person-months (95% CI, 7.69–8.93), 47.91/100 person-months (95% CI, 44.22–51.58), and 682.11/100 person-months (95% CI, 635.49–728.52), respectively. The sole identified independent factor related to the incidence of heat-related illnesses was a BMI ≥30 kg/m² (adjusted IRR = 2.66, 95% CI, 1.01–7.03). In conclusion, a high BMI was associated with heat-related illnesses among conscripts undergoing basic training in Thailand. Daily monitoring of heat-related illnesses, body temperature, body weight and urine color in each new conscript during basic military training was feasible.

Novel Factors Associated With Analgesic and Anti-inflammatory Medication Use in Distance Runners: Pre-race Screening Among 76 654 Race Entrants-SAFER Study VI

OBJECTIVE

Analgesic/anti-inflammatory medication (AAIM) increases the risk of medical complications during endurance races. We determined how many runners use AAIM before or during races, AAIM types, and factors associated with AAIM use.

DESIGN

Cross-sectional study.

SETTING

21.1-km and 56-km races.

PARTICIPANTS

Seventy-six thousand six hundred fifty-four race entrants.

METHODS

Participants completed pre-race medical screening questions on AAIM use, running injury or exercise-associated muscle cramping (EAMC) history, and general medical history.

MAIN OUTCOME MEASURES

Analgesic/anti-inflammatory medication use, types of AAIM (% runners; 95% confidence interval), and factors associated with AAIM use (sex, age, race distance, history of running injury or EAMC, and history of chronic diseases) [prevalence ratio (PR)].

RESULTS

Overall, 12.2% (12.0-12.5) runners used AAIM 1 week before and/or during races (56 km = 18.6%; 18.0-19.1, 21.1 km = 8.3%; 8.1-8.6) (P < 0.0001). During races, nonsteroidal anti-inflammatory drugs (NSAIDs) (5.3%; 5.1-5.5) and paracetamol (2.6%; 2.4-2.7) were used mostly. Independent factors (adjusted PR for sex, age, and race distance; P < 0.0001) associated with AAIM use were running injury (2.7; 2.6-2.9), EAMC (2.0; 1.9-2.1), cardiovascular disease (CVD) symptoms (2.1; 1.8-2.4), known CVD (1.7; 1.5-1.9), CVD risk factors (1.6; 1.5-1.6), allergies (1.6; 1.5-1.7), cancer (1.3; 1.1-1.5), and respiratory (1.7; 1.6-1.8), gastrointestinal (2.0; 1.9-2.2), nervous system (1.9; 1.7-2.1), kidney/bladder (1.8; 1.6-2.0), endocrine (1.5; 1.4-1.7), and hematological/immune (1.5; 1.2-1.8) diseases.

CONCLUSIONS

12.2% runners use AAIM before and/or during races, mostly NSAIDs. Factors (independent of sex, age, and race distance) associated with AAIM use were history of injuries, EAMC, and numerous chronic diseases. We suggest a pre-race screening and educational program to reduce AAIM use in endurance athletes to promote safer races.

Physiological and perceptual responses in the elderly to simulated daily living activities in UK summer climatic conditions

OBJECTIVES

The elderly population is at an increasingly significant health risk to heat-related illnesses and mortality when compared with younger people in the same conditions. This is due to an increased frequency and severity of heatwaves, attributed to climate change, and reduced ability of elderly individuals to dissipate excess heat. Consequently, most excess deaths and emergency visits during heatwaves occur in people aged more than 65 years. The aim of this investigation was to assess the physiological and perceptual responses of elderly people during exercise sessions equating to activities of daily living in UK summer climatic conditions.

STUDY DESIGN

Mixed-method, randomised research design.

METHODS

Twenty-eight participants (17 males, 10 females and 1 transgender female) were randomly assigned into three experimental groups; 15°C, 25°C or 35°C, with 50% relative humidity. Participants completed one preliminary and three experimental trials within their assigned environment. The data from the preliminary incremental recumbent cycling test was used to calculate participant's individual exercise intensities equating to 2, 4 and 6 metabolic equivalents (METs) for the subsequent trials. During experimental trials, participants completed 30-min seated rest and 30-min cycling.

RESULTS

No change was observed in thermal comfort ([TC] just uncomfortable in both trials), and only modest changes in ratings of perceived exertion (14 ± 2 vs 15 ± 2) at 6 METs in 25°C compared with those in 35°C were observed. In contrast, thermal strain markers did significantly increase (P < 0.05) across the same conditions, including change in rectal temperature (ΔT_re) during exercise (0.27 ± 0.17°C vs 0.64 ± 0.18°C) and peak skin temperature ([T_skin] 32.94 ± 1.15°C vs 36.11 ± 0.44°C).

CONCLUSION

When completing exercise that equates to activities of daily living, elderly people could have a decreased perceptual awareness of the environment even though physiological markers of thermal strain are elevated. Consequently, the elderly could be less likely to implement behavioural thermoregulation interventions (i.e. seek shade and/or remove excess layers) due to a decreased awareness of an increasingly thermally challenging environment.

Fire service instructors' working practices: A UK survey

Analysis of Fire Service Instructors (FSI) working practices and health is needed to minimise health risks related to heat illness, cardiovascular events and immunological stress. Online surveys were distributed to UK FSI and Firefighters (FF). One hundred and thirty FSI (age: 43 ± 7yrs) and 232 FF (age: 41 ± 8yrs) responded. FSI experienced 2-10 live fires per week, with 45% of FSI reporting management does not set a limit on the number of exposures. Few FSI followed hydration guidelines, or cooling methods. New symptoms of ill health were reported by 41% of FSI and 21% of FF. FSI with ≥11 Breathing Apparatus exposures per month were 4.5 times (95% CI 1.33-15.09) more likely to experience new symptoms. A large proportion of FSI are experiencing new symptoms of illness after starting their career, and guidelines on exposure and hydration are not universally in place to reduce the risk of future health problems.

Heat: a primer for public health researchers

OBJECTIVES

To provide a primer on the physical characteristics of heat from a biometeorological perspective for those interested in the epidemiology of extreme heat.

STUDY DESIGN

A literature search design was used.

METHODS

A review of the concepts of heat, heat stress and human heat balance was conducted using Web of Sciences, Scopus and PubMed.

RESULTS

Heat, as recognised in the field of human biometeorology, is a complex phenomenon resulting from the synergistic effects of air temperature, humidity and ventilation levels, radiation loads and metabolic activity. Heat should therefore not be conflated with high temperatures. A range of empirical, direct and rational heat stress indices have been developed to assess heat stress.

CONCLUSION

The conceptualisation of heat stress is best described with reference to the human heat balance which describes the various avenues for heat gain to and heat loss from the body. Air temperature alone is seldom the reason for heat stress and thus heat-related health effects.

Heat stress incident prevalence and tennis matchplay performance at the Australian Open

OBJECTIVES

To examine the association of wet bulb globe temperature (WBGT) with the occurrence of heat-related incidents and changes in behavioural and matchplay characteristics in men's Grand Slam tennis.

DESIGN

On-court calls for trainers, doctors, cooling devices and water, post-match medical consults and matchplay characteristic data were collected from 360 Australian Open matches (first 4 rounds 2014-2016).

METHODS

Data were referenced against estimated WBGT and categorised into standard zones. Generalised linear models assessed the association of WBGT zone on heat-related medical incidences and matchplay variables.

RESULTS

On-court calls for doctor (47% increase per zone, p=0.001), heat-related events (41%, p=0.019), cooling devices (53%, p<0.001), and post-match heat-related consults (87%, p=0.014) increased with each rise in estimated WBGT zone. In WBGT's >32°C and >28°C, significant increases in heat-related calls (p=0.019) and calls for cooling devices (p<0.001), respectively, were evident. The number of winners (-2.5±0.006% per zone, p<0.001) and net approaches (-7.1±0.008%, p<0.001) reduced as the estimated WBGT zone increased, while return points won increased (1.75±0.46, p<0.001). When matches were adjusted for player quality of the opponent (Elo rating), the number of aces (5±0.02%, p=0.003) increased with estimated WBGT zone, whilst net approaches decreased (7.6±0.013%, p<0.001).

CONCLUSIONS

Increased estimated WBGT increased total match doctor and trainer consults for heat related-incidents, post-match heat-related consults (>32°C) and cooling device callouts (>28°C). However, few matchplay characteristics were noticeably affected, with only reduced net approaches and increased aces evident in higher estimated WBGT environments.

Influence of Rhodiola rosea on the heat acclimation process in young healthy men

The adaptogen Rhodiola rosea (RR) may mitigate stress responses and have beneficial effects on endurance capacity (EC) and mental performance. Heat acclimation (HA) improves EC in the heat, but the potential impact of RR on the HA process is unknown. Therefore, our intent was to determine if RR has a positive impact on HA. Twenty male subjects (age, 22.5 ± 3.0 years) completed 2 EC tests involving walking (6 km·h^-1) until volitional exhaustion in a climate chamber (air temperature, 42 °C; relative humidity, 18%) before (H1) and after (H2) an 8-day HA period. One group (SHR; n = 10) ingested standardised extract SHR-5 of RR (a single daily dose of 432 mg), while a second group (PLC; n = 10) administered a placebo prior to each HA session. Efficacy of HA was evaluated on the basis of changes that occurred from H1 to H2 in the time to exhaustion (TTE), exercise heart rate (HR), core and skin temperatures (T_c, T_sk), stress hormones, ratings of perceived exertion (RPE) and fatigue (RPF), and thermal sensation (TS). HA significantly increased TTE (133.1 ± 44.1 min in H1; 233.4 ± 59.8 min in H2; p < 0.0001) and decreased (p < 0.0001) HR, T_c, T_sk, stress hormones as well as RPE, RPF, and TS. However, the magnitude of all these changes was similar (p > 0.05) in the SHR and PLC groups. These results suggest that the use of RR during HA has no beneficial performance, physiological, or perceptual effects in young healthy males.

Neurologic Injuries in Noncontact Sports

Noncontact sports are associated with a variety of neurologic injuries. Concussion, vascular injury (arterial dissection), and spinal cord trauma may be less common in noncontact sports, but require special attention from the sports neurologist. Complex regional pain disorders, muscle injury from repetitive use, dystonia, heat exposure, and vascular disorders (patent foramen ovale), occur with similar frequency in noncontact and contact sports. Management of athletes with these conditions requires an understanding of the neurologic consequences of these disorders, the risk of injury with return to play, and consideration for the benefits of exercise in health restoration and disease prevention.

Role of work uniform in alleviating perceptual strain among construction workers

This study aims to examine the benefits of wearing a new construction work uniform in real-work settings. A field experiment with a randomized assignment of an intervention group to a newly designed uniform and a control group to a commercially available trade uniform was executed. A total of 568 sets of physical, physiological, perceptual, and microclimatological data were obtained. A linear mixed-effects model (LMM) was built to examine the cause-effect relationship between the Perceptual Strain Index (PeSI) and heat stressors including wet bulb globe temperature (WBGT), estimated workload (relative heart rate), exposure time, trade, workplace, and clothing type. An interaction effect between clothing and trade revealed that perceptual strain of workers across four trades was significantly alleviated by 1.6-6.3 units in the intervention group. Additionally, the results of a questionnaire survey on assessing the subjective sensations on the two uniforms indicated that wearing comfort was improved by 1.6-1.8 units when wearing the intervention type. This study not only provides convincing evidences on the benefits of wearing the newly designed work uniform in reducing perceptual strain but also heightens the value of the field experiment in heat stress intervention studies.