Heat Acclimation Research Articles

Proposing adjustments to heat safety thresholds for junior high and high school sports clubs in Japan.

With higher temperatures expected in the future due to global climate change, addressing health risks such as heat illness is increasingly important. In Japan, thousands of heat illness cases occur annually during school sports club activities. The risk may vary by sport, location, and region, but how heat safety thresholds (HSTs) should be adjusted to provide effective guidelines remains uncertain. Thus, we conducted a case-crossover study using data of heat illness cases and wet-bulb globe temperature (WBGT) throughout Japan to evaluate the heat illness risk for the current HSTs and propose adjustments. A significant relationship was found between heat illness incidence and WBGT at the time of the incident, as well as the average WBGT one and two days prior. The risk significantly varies with factors such as club, region, location, year, month, and the average WBGT in summer. Therefore, we recommend lowering the current HSTs by one category (3°C) in the following cases: (1) clubs at high risk (baseball, softball, soccer/futsal, tennis, track and field, kyudo, and other with sustained exercise or thick uniforms); (2) from April to June; (3) in cooler regions (Hokkaido, Tohoku, Hokuriku, or where the average WBGT in summer≦18℃); (4) for outdoor activities; (5) when heat rapidly increases without adequate heat acclimatization. These findings may inform educators, students, sports authorities, and policymakers in adjusting HSTs to reduce the incidence of heat illness, thereby ensuring safer environments for school sports activities.

Combined active and passive isothermic heating leads to similar core temperature compared to exercise alone.

The training stress of heat acclimatization optimizing exercise performance in a hot environment can be demanding. This study evaluated the efficiency of different single heating protocols to elevate core temperature. Not randomized controlled trial. Passive heating (PAS), 30-min active heating using a high-intensity bike protocol (HIBP) in a hot environment with 30-min passive heating (EH-PAS), 60-min HIBP in a hot environment (EH), or 60-min HIBP at room temperature (EM). Ten male participants (25±3 years) performed four different 60-min heating strategies at least one week apart. Body core temperature and heart rate. The highest peak gastrointestinal temperature occurred in EH-PAS (39.1±0.4°C), followed by EH (38.9±0.3°C), EM (38.4±0.3°C), and PAS (38.1±0.5°C). The average HR, measured as a control for intensity, was not different between exercise strategies (EH-PAS: 142±12.3, EH: 146±9.7, and EM: 142±13.3, p>0.05), while different from PAS: 98±15.2 bpm, p<0.05. Adding passive heating to a shorter exercise protocol can be just as effective in keeping core temperature elevated as exercise in the heat alone during a 60-minute session. Therefore, a single-bout combination of exercise and passive heating may result in a similar body temperature induction compared to exercise heat stress alone.

USING PREDICTIVE ANALYTICS TO IMPROVE SURVEILLANCE OF HEAT-RELATED ILLNESS DURING MILITARY TRAINING

Background: Heat-related illnesses are a critical concern for military personnel, especially those unfamiliar with hot climate regions. The Royal Thai Army (RTA) implements a 10-week military training program encompassing four phases: (1) Heat acclimatization training, (2) Combat fundamentals and unarmed combat training, (3) Armed combat training and tactical training, and (4) Field training exercise and evaluations. Objective: This study aimed to conduct a predictive analysis of heat-related illnesses to enhance prevention programs. Methods: The study utilized secondary data from the RTA Medical Department, incorporating variables such as age, occupation, education, underlying diseases, smoking and alcohol consumption, sleep duration, exercise, medication history, body mass index (BMI), weight loss, body temperature, dark urine, heat rash, and environmental humidity. Multiple machine learning algorithms were employed to develop predictive models. Results: The samples comprised 809 male recruits (103,051 encounters) with an average age of 22. Approximately 12% of the recruits had a BMI ≥30 kg/m2, while nearly 70% and 90% reported tobacco use and alcohol consumption in the past 12 months, respectively. Among the recruits, 16% reported substance use within the preceding 30 days. The eXtreme Gradient Boosting (XGB) model achieved 91% accuracy in predicting heat-related illnesses before Phase 2. The top five predictive variables were Lopburi Province (central region), Songkhla Province (southern region), and Bangkok (capital city), sleep duration before joining military training (hours), and age (years). Conclusion: This study, which applied machine learning techniques to predict heat-related illnesses among Thai recruits, can potentially impact the health and training of military personnel. The comparative analysis of various algorithms identified the XGB model as the optimal performer in predicting heat-related illnesses during the combat fundamentals and unarmed combat training phase. However, it is essential to note that further study is needed to enhance the applicability of our predictive model, which includes expanding its use to new cohorts of Thai conscripts, underscoring our research’s ongoing nature.

In ovo betaine and heat acclimation affect hatching results, growth performance and immunity of the broilers under cyclicheatstress.

This study investigated the effects of in ovo betaine and thermal manipulation during incubation on growth performance, and some immune parameters of broilers under cyclic heat stress (CHS). Eggs were divided into 5 groups and incubated at 1) 37.8°C and 60% relative humidity (Control incubation and not-injected, CI); 2) eggs were incubated at CI and in ovo betaine injected into yolk sac on d 11 (E11) (CI + In ovo); 3) eggs were exposed to 38.8°C for 8h between 10 and 18d of incubation (heat acclimation, HA); 4) eggs were incubated at HA and in ovo betaine applied (HA + In ovo); 5) positive control: eggs were incubated at CI and injected with saline. Hatched chicks were raised under standard management conditions until 21 d, between 21 and 42 d half of the chickens in each incubation treatment were kept either at optimum (OPT) or at CHS. In ovo and HA did not affect hatching performance. In ovo increased thymus and spleen weights of chicks. Serum IgG was higher in HA + In ovo chicks. From d 7 to 21, in ovo chicks were heavier body weights, consumed more feed, and better feed conversion than those from CI. The body weights of HA chickens were similar in OPT and CHS on d 28 and 35. CHS reduced the body weight of CI chickens which was compatible with their feed consumption. Moreover, feed intake of HA + In ovo chickens exposed to CHS was higher than those not injected indicating that HA + In ovo enhanced thermoregulation of chickens under CHS.

Preserving Athletic Performance at Altitude with Heat Acclimation: A Cross-Adaptive Approach

Preserving Athletic Performance at Altitude with Heat Acclimation: A Cross-Adaptive Approach

Implementation of a mixed-methods heat acclimation programme in a professional soccer referee before the 2022 FIFA world cup in Qatar: a case study

ObjectivesThis case study reports the real-world practicalities of implementing a mixed-methods heat acclimation (HA) programme before the 2022 FIFA World Cup.MethodsOne male English soccer referee (age: 44 years; height: 1.82...

Heat Acclimation By Warm-water Immersion Enhances Whole-body Heat Loss In Older Adults

Heat Acclimation By Warm-water Immersion Enhances Whole-body Heat Loss In Older Adults

Constructing A Makeshift Heat Chamber Suitable For Thermoregulatory Research And Heat Acclimation Training

Constructing A Makeshift Heat Chamber Suitable For Thermoregulatory Research And Heat Acclimation Training

Influence Of Heat Acclimation On Aerobic Performance In Cool, Hot And Hypoxic Conditions

Influence Of Heat Acclimation On Aerobic Performance In Cool, Hot And Hypoxic Conditions

Feasibility Of Heat Acclimation In Wildland Firefighters

Feasibility Of Heat Acclimation In Wildland Firefighters

Heat Acclimation Attenuates Ferroptosis and Prevents Heat Stress-Induced AKI by Enhancing Mitophagy

Heat Acclimation Attenuates Ferroptosis and Prevents Heat Stress-Induced AKI by Enhancing Mitophagy

Perceived Thermal Comfort Of Collegiate Marching Band Artists Completing A Heat Acclimatization Protocol

Perceived Thermal Comfort Of Collegiate Marching Band Artists Completing A Heat Acclimatization Protocol

Selection of Reference Genes and HSP17.9A Expression Profiling in Heat-Stressed Grapevine Varieties

Background: “Touriga Franca” (TF) and “Touriga Nacional” (TN) are grapevine varieties cultivated in the ‘Douro Superior’ subregion (Northern Portugal) that experience stressful environmental conditions during the summer. Objectives: Aiming to profile the expression of stress-responsive genes by quantitative real-time PCR (qPCR) in TF and TN plants growing naturally, three candidate reference genes were first tested under controlled conditions. Methods: To simulate a summer’s day, TF and TN in vitro plants were exposed to 32 °C–3 h (heat acclimation) and 42 °C–1 h (severe heat stress, HS) followed by two recovery periods (32 °C–3 h and 24 °C–24 h). Leaf samples were collected at the end of each phase. Control plants were kept at 24 °C. Results: Among the candidate reference genes, the UBC and VAG pair showed the highest stability. The suitability of these genes for qPCR was validated by heat shock protein 17.9A (HSP17.9A) gene profiling. The HSP17.9A expression was up-regulated in both varieties and all experimental phases except in TF control plants. TN showed the highest HSP17.9A relative expression ratio after severe HS. Conclusions: TN responded faster than TF to the induced heat shocks. The UBC, VAG, and HSP17.9A genes revealed to be suitable for further qPCR assays in TF and TN grapevine varieties.

Random forest analysis of the relative importance of meteorological indicators for heatstroke cases in Japan based on the degree of severity and place of occurrence

Heatstroke is a serious health concern in Japan. To reduce heatstroke risk, the government of Japan implemented the “Heatstroke Alert” nationwide in 2021, employing the wet bulb globe temperature (WBGT) as a criterion. Although the WBGT is a useful meteorological indicator for assessing the risk of heatstroke, other important meteorological indicators must also be investigated. Therefore, using a random forest approach, this study analyzed the relative importance of several meteorological indicators, including those representing heat acclimatization, for each of the 47 Japanese prefectures. Using the generalized linear model, important meteorological indicators were employed as explanatory variables in the heatstroke prediction model to determine the predictive meteorological indicator. Heatstroke cases were evaluated separately by the degree of severity and the place of occurrence. The results showed that the relative temperature (RelTemp), which represents heat acclimatization and was calculated considering past temperature history, was the most predictive (i.e., provided the best goodness of fit) concerning the degree of severity, place of occurrence, and prefectures. RelTemp can be a complementary indicator of WBGT in countries and regions such as Japan, where seasonal differences in heat acclimatization must be considered. In addition, the findings of this study contribute to the development of a more accurate assessment of heatstroke risk.

The Impact of Heat Exposure on the Health and Performance of Soccer Players: A Narrative Review and Bibliometric Analysis.

The impact of heat exposure on the health and performance of soccer players is a widely discussed topic. The purpose of this study is to provide a comprehensive overview of the international literature that has addressed this issue. To achieve this objective, we initially conducted a bibliometric analysis and a literature review of the main topics that emerged through bibliometric techniques. For the bibliometric analysis, we employed VOSviewer software (version 1.6.20.0) and used documents found in the Scopus database. The analysis ultimately included 133 documents published in 66 sources. Key journals and authors were identified, highlighting significant contributions to the field. Science mapping revealed collaboration networks and research focus areas such as physical health, safety, soccer performance, dehydration and hydration, physiological mechanisms and monitoring, nutrition, fluid intake, and cooling techniques. Based on the key areas highlighted in the identified clusters, which emerged from the co-occurrence analysis of the author keywords, the following three topics were developed in the literature review: (a) the physiology and health of football players; (b) performance impacts; and (c) strategies to prevent negative consequences. The review showed that high heat exposure can reduce the physical and cognitive performance of athletes and prove detrimental to their health. To mitigate the negative consequences, appropriate hydration strategies, heat acclimatization, and cooling techniques have been proposed. Our findings provide the international scientific community with comprehensive knowledge of the existing literature, laying the foundation for future research while simultaneously offering coaches and athletes the necessary theoretical knowledge to help improve safety and performance.

The effect of seasonal heat acclimatization on cool-seeking behaviour during passive heat stress in young adults.

Seasonal heat acclimatization is known to enhance autonomic thermoeffector responses, whereas the behavioural response following seasonal heat acclimatization remains unknown. We investigated whether seasonal heat acclimatization would alter autonomic and behavioural thermoregulatory responses. Sixteen healthy participants (eight males and eight females) underwent two trials involving 50 min of lower-leg passive heating (lower-leg submersion in 42°C water) with (Fan trial) and without (No fan trial) the voluntary use of a fan in a moderate thermal environment (27°C, 50% relative humidity) across winter and summer months. In Fan trials, participants were allowed to use a fan to maintain thermal comfort, but this was not allowed in the No fan trials. Cool-seeking behaviour was initiated at a lower change in rectal temperature [mean (SD): 0.21 (0.18)°C vs. 0.11 (0.13)°C, P=0.0327] and change in mean skin temperature [2.34 (0.56)°C vs. 1.81 (0.32)°C, P<0.0001], and cooling time was longer [16.46 (5.62) vs. 20.40 (4.87) min, P=0.0224] in summer compared with winter. However, thermal perception was not modified by season during lower-leg passive heating (all P>0.0864). Furthermore, rectal temperature was higher in summer (P=0.0433), whereas mean body temperature and skin temperature were not different (all P>0.0631) between the two seasons in Fan trials. In conclusion, seasonal heat acclimatization enhanced the cool-seeking behaviour from winter to summer.

Wheat TaNACα18 functions as a positive regulator of high-temperature adaptive responses and improves cell defense machinery.

Global wheat production amounted to >780 MMT during 2022-2023 whose market size are valued at >$128 billion. Wheat is highly susceptible to high-temperature stress (HTS) throughout the life cycle and its yield declines 5-7% with the rise in each degree of temperature. Previously, we reported an array of HTS-response markers from a resilient wheat cv. Unnat Halna and described their putative role in heat acclimation. To complement our previous results and identify the key determinants of thermotolerance, here we examined the cytoplasmic proteome of a sensitive cv. PBW343. The HTS-triggered metabolite reprograming highlighted how proteostasis defects influence the formation of an integrated stress-adaptive response. The proteomic analysis identified several promising HTS-responsive proteins, including a NACα18 protein, designated TaNACα18, whose role in thermotolerance remains unknown. Dual localization of TaNACα18 suggests its crucial functions in the cytoplasm and nucleus. The homodimerization of TaNACα18 anticipated its function as a transcriptional coactivator. The complementation of TaNACα18 in yeast and overexpression in wheat demonstrated its role in thermotolerance across the kingdom. Altogether, our results suggest that TaNACα18 imparts tolerance through tight regulation of gene expression, cell wall remodeling and activation of cell defense responses.

Nutritional Considerations in Exercise-Based Heat Acclimation: A Narrative Review.

In addition to its established thermoregulatory and cardiovascular effects, heat stress provokes alterations in macronutrient metabolism, gastrointestinal integrity, and appetite. Inadequate energy, carbohydrate, and protein intake have been implicated in reduced exercise and heat tolerance. Classic exercise heat acclimation (HA) protocols employ low-to-moderate-intensity exercise for 5-14days, while recent studies have evolved the practice by implementing high-intensity and task-specific exercise during HA, which potentially results in impaired post-HA physical performance despite adequate heat adaptations. While there is robust literature demonstrating the performance benefit of various nutritional interventions during intensive training and competition, most HA studies implement few nutritional controls. This review summarizes the relationships between heat stress, HA, and intense exercise in connection with substrate metabolism, gastrointestinal function, and the potential consequences of reduced energy availability. We discuss the potential influence of macronutrient manipulations on HA study outcomes and suggest best practices to implement nutritional controls.

Species-specific effects of light and temperature on photosynthesis and respiration among Symbiodiniaceae (Dinophyceae)

Coral reefs are exposed to various environmental stressors that cause bleaching events, whereby endosymbiotic microalgae (Symbiodiniaceae) disassociate from coral hosts. Bleached corals are compromised and face mortality. The combination of high-light exposure and elevated seawater temperature often lead to coral bleaching. The physiological properties of the Symbiodiniaceae within the coral tissues contribute to the thermal tolerance of the holobiont (the host and all its symbionts). The present study aimed to investigate the effects of light and temperature stress on four Symbiodiniaceae species from three genera with respect to photosynthetic oxygen production and consumption. Under control conditions, the species displayed predominantly low-to-moderate light requirements for photosynthesis with increased photoinhibition at higher photon flux rates. After 30 days of heat acclimation at 32 °C, maximum photosynthetic activity declined in Effrenium voratum, doubled in Fugacium kawagutii, and remained unchanged in Breviolum psygmophilum. In subsequent acute heating assays, species-specific effects on maximum photosynthetic activity were observed. Photosynthesis in all species declined across a temperature gradient between 25 and 39 °C in the acute heating assays; full inhibition occurred at 37 °C in B. psygmophilum and E. voratum and at 39 °C in B. aenigmaticum and F. kawagutii. In contrast, respiration remained largely constant in all species across temperatures. Our data point to species-specific photophysiological traits that lead to different thermal tolerances among Symbiodiniaceae.

Factors contributing to heat tolerance in humans & experimental models.

Understanding physiological mechanisms of tolerance to heat exposure, and potential ways to improve such tolerance, is increasingly important in the context of ongoing climate change. We discuss the concept of heat tolerance in humans and experimental models (primarily rodents), including intracellular mechanisms and improvements in tolerance with heat acclimation.