Heat Tolerance Test Research Articles

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...

The Significance of Body Surface Area to Mass Ratio for Thermal Responses to a Standardized Exercise-Heat Stress Test.

To evaluate the significance of body surface area-to-mass ratio (BSA/mass) on the heat-tolerance test (HTT) results. We hypothesized that individuals defined as heat tolerant (HT) would have on average higher BSA/mass compared to heat intolerant (HI) individuals. A retrospective reanalysis of the HTT results of 517 soldiers (age: 18-38 yrs., M/F: 96/4%), who were tested by the Israel Defense Forces (IDF) HTT protocol. The criterion for heat tolerance in the current analysis was a rectal temperature (Tre) plateau during the second hour of the test. A logistic regression analysis to evaluate the predictive power of BSA/mass for heat intolerance was performed; the spline model was applied to show the odds for heat intolerance across BSA/mass. In men BSA/mass of HI individuals was lower than HT individuals (248 ± 19 vs. 262 ± 18 cm2/kg, p < 0.01, d = 0.76). In women a similar trend was noted but with no statistical significance between HT and HI groups. The odd ratio for heat intolerance for every unit increase in BSA/mass was 0.97 (CI 95% 0.95-0.99). The spline model plateaued above BSA/mass of 270 cm2/kg. The results imply that body-core temperature responses to a standard exercise-heat stress (fixed external work rate and climatic conditions) are influenced by BSA/mass. More specifically, lack of a steady state in Tre (indicating heat intolerance) was more likely to occur with every unit decrease in BSA/mass. These findings contribute to a better understanding of the role of body anthropometry in the response to a standard exercise-heat task that might have an implication on clinical decision-making about return to duty/play of soldiers, athletes and others who deemed to be identified as HI.

Skeletal Muscle Mitochondrial Function and Mitochondria-related Protein Expression in Men and Women During Acute Exercise-Heat Stress and Acclimation

INTRODUCTION: Military personnel can exhibit improved performance and reduced physiological strain in hot environments with the induction of heat adaptations. Mild heat exposure at 40°C heat serves therapeutic purposes, enhancing metabolic flexibility, and promoting positive muscle adaptations. Research indicates that heat acclimation (HA) leads to increased mitochondrial biogenesis and reduced reactive oxygen species in skeletal muscle, improving thermal tolerance. However, understanding sex differences in mitochondrial function and related protein expression affected by heat acclimation remain limited. Therefore, this study aimed to explore mitochondrial respiration and the expression of mitochondria-related proteins to better understand the impact of heat stress on mitochondrial adaptations in skeletal muscle in both males and females. METHODS: Healthy men (M:n = 7, 22±2yo, VO2max 52.86±2.35ml·kg−1·min−1) and women (F:n = 7, 24±1yo, VO2max 45.97±2.57 ml·kg−1·min−1) participated in a 5-day heat acclimation (HA) at 40°C and 40% relative humidity. Before and after HA, participants completed a heat tolerance test (HTT) measuring time to reach a rectal temperature of 39.5°C or volitional failure. Biopsies from the vastus lateralis were taken immediately post-HTT for musculoskeletal analysis. Mitochondrial respiratory function was assessed using Oroboros O2K, employing high-resolution respirometry. Paired sample t-tests were used to determine statistical significance between groups (p&lt;0.05). Proteomics data were mined for Gene Ontology (GO) terms related to mitochondrial function (STRING V.12.0) (adjusted p&lt;0.05). RESULTS: Both men and women exhibited significant enhancements in complex I-mediated respiration and complex I+II maximal coupled respiration after HA (PRE-HA: M:P=0.009, P=0.026; F:P=0.016, P=0.011). No sex differences in mitochondria respiration were observed before or after HA. Before HA, skeletal muscle from women showed higher expression in 4 proteins (ND61, NDUFB1, COX1, ATP5MF) associated with 9 GO terms related to mitochondrial function compared to men. However, after HA, men exhibited higher expression in 14 proteins (MTX2, APOOL, DNAJC11, TIMM13, NDUFAB1, DNAJC11, MAVS, CHCHD4, NDUFAF4, ATP5PF, NDUFAS, UQCRH, SSBP1, ND3) associated with 21 mitochondria-related GO terms compared to women. CONCLUSION: Acclimation to heat stress is associated with positive mitochondrial adaptation in both men and women. Although enhancements in mitochondrial respiratory function in both men and women after HA, there were different skeletal muscle responses between men and women regarding the regulation of mitochondria-related proteins after a bout of exercise-heat stress. Funding: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Sexual Dimorphism in the Slope of Rectal Temperature Rise Before Heat Acclimation, but Not After Heat Acclimation

Purpose: Our study aimed to identify if sexual dimorphism exists surrounding the slope of rectal temperature rise during a steady state exercise in the heat before and after heat acclimation (HA). In this study, we hypothesized that women would have a greater tolerance to heat stress resulting from a lesser slope of rectal temperature rise when compared to men. Methods: Physically active men (M) (n=12, VO2max: 51.3 ± 6.1 mL·kg−1·min−1, Age: 21±2 yo) and women (W) (n=12, VO2max: 44.2±5.8±6.1 mL·kg−1·min−1, Age: 24±4 yo) completed a steady state treadmill based heat tolerance test (HTT) (3 mph 2% grade for 120 minutes (min) in 40°C, 40% relative humidity). Rectal temperature (Trec) was collected during the first 10-min (PreHAF) and the last 10-min (PreHAL) of the HTT before HA, as well as the first 10-min (PostHAF) and last 10-min (PostHAL) after HA. The slope of rectal temperature rise for the first 10min was calculated by taking the difference of Trec at 10min and 0min, with the slope for the last 10min calculated using Trec at 120min and 110min. Both Trec differences were divided by 10min to obtain the slope in °C/min. One tailed independent T-tests were used to determine sex differences and dependent T-tests to determine differences within sex, both with significance at p≤0.05. All data are presented as mean ± SD. Results: Before acclimation, W demonstrated a greater slope of Trec rise PreHAF when compared to M (M: 0.01 ± 0.02°C/min, W: 0.03 ± 0.01°C/min, p=0.006) with opposite findings PreHAL (M: 0.01 ± 0.01°C/min, W: 0.00 ± 0.00°C/min, p=0.046). Following HA, there were no differences between the slope of Trec rise in M vs. W at both PostHAF (M: 0.02 ± 0.01°C/min, W: 0.02 ± 0.01°C/min, p&gt;0.05) and PostHAL (M: 0.00 ± 0.01°C/min, W: 0.00 ± 0.00°C/min, p&gt;0.05). In M, the PreHAL slope of Trec rise was greater than PostHAL (PreHAL: 0.01 ± 0.01°C/min, PostHAL: 0.00 ± 0.01°C/min, p=0.019), with no differences found within the first 10min (PreHAF: 0.01 ± 0.01°C/min, PostHAF: 0.02 ± 0.01°C/min, p=0.060). No differences in the slope of Trec rise between HA statuses were found in W (PreHAF: 0.03 ± 0.01°C/min, PostHAF: 0.02 ± 0.01°C/min, p&gt;0.05; PreHAL: 0.00 ± 0.01°C/min, PostHAL: 0.00 ± 0.01°C/min, p&gt;0.05). Conclusion: Consistent with previous literature, men exhibit better adaptations displayed by greater reductions in rectal temperature after HA, while women demonstrated consistent responses in both the first and last 10-min. These findings contribute to our understanding of sex-specific physiological adaptations to heat acclimation and underscore the importance of considering sex-based differences in heat-related research and interventions. Funding: DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Skeletal muscle proteomics responses in men and women during acute exercise-heat stress and acclimation

Purpose: Our broad aim was to identify targetable mechanisms of improving skeletal muscle function and recovery during exercise-heat stress. In this study, we used proteomics to test the hypothesis that skeletal muscle proteomic changes would correspond to acclimation state. Methods: Healthy men (M: n = 7, 22 ± 2 yo, VO2max 52.86 ± 2.35 ml·kg−1·min−1) and women (F: n = 7, 24 ± 1 yo, VO2max 45.97 ± 2.57 ml·kg−1·min−1) completed a 5-day heat acclimation (HA) (40 °C, 40% rH). Before and after HA, participants completed a heat tolerance test measuring time to reach rectal temperature 39.5°C (HTT39.5) or failure (stoppage). Musculoskeletal biopsies from the vastus lateralis were harvested for protein extraction, quantification, and digestion prior to untargeted UPLC-MS/MS (Q Exactive HF). Peptide identification and label-free quantitation was achieved using Andromeda search engine and MaxQuant (v1.6.10.43), using UniProt reference proteome UP0000005640. All search results were filtered to FDR (false discovery rate) 1% and uploaded to Scaffold v5.1.0 for data visualization and t-test analyses for difference between conditions (p &lt; 0.05). Functional annotation and pathway analysis were conducted (DAVID, Reactome, String). Physiological, perceptual, and performance metrics were statistically analyzed using t-tests (p ≤ 0.05). Results: No significant differences (p = 0.931) were observed between males (mean = 27.21 ± 1.37 minutes) and females (26.91 ± 3.20 minutes) for PREHA HTT39.5. HTT39.5 for F was significantly higher than for men at PREHA (p = 0.001) and POSTHA (p = 0.014). 2741 proteins from 960,731 spectra were detected among our skeletal muscle biopsy samples with 22 and 33 proteins expressed more highly in M and F at PREHA, respectively. 149 and 81 proteins were more highly expressed in M and F, respectively, at POSTHA. Differences between M and F included more highly connected nodes in M at PREHA (average node degree: 3.7, avg. local clustering coeffcient: 0.529, PPI enrichment p-value &lt; 1.11e-16, HIST1H3 (isoforms D, H, and J), HIST1H4F, HIST2H2A (isoforms C, B, and E), HIST2HAC, H2AFX) and at POSTHA (average node degree: 4.26, avg. local clustering coeffcient: 0.455, expected number of edges 110, PPI enrichment p-value &lt; 1.0e-16, GAPDH, RPS13, TPI1, PKM, RPS21). Differences in F and M (more highly expressed) also included GO terms related to DNA, RNA, and protein quality regulation and immune function and metabolism (p &lt; 0.05). Conclusions: Acclimation is associated with different skeletal muscle responses in M and F related to protein synthesis and immune function pathways that are regulated after a bout of exercise-heat stress. Ongoing analysis examines relationships between naïve or acclimated state and individual skeletal muscle proteomic profiles. DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Biological Sex Differences in Heat Acclimation and Gut Microbiome Responses

Purpose: Our broad aim was to elucidate the relationship between gut microbiome (gMB) and heat tolerance/acclimation. In this study, we hypothesized that the gMB is affected by acute exercise-heat stress/acclimation and is biologically sex-specific. Methods: Physically active men (M: n=10, 21±2yo, VO2max 51.8±6.6mL−1·kg−1·min−1) and women (W: n=6, 26±5yo, VO2max 45.5±8.0mL−1·kg−1·min−1) completed a modified heat tolerance test (HTT; 65% vVO2max, 2% grade treadmill run, 40°C, 40% relative humidity) until rectal temperature reached 39.5°C (TT39.5) or failure before (preHA) and after (postHA) a 5-day heat acclimation (HA). DNA from stool samples was sequenced via 16S rRNA (V4). a-diversity (Shannon Index) and rarified abundances of phyla, family, and genus were calculated by subsampling to 10,000 reads per sample. Blood inflammation markers were measured with commercially available kits. Significant differences (p≤0.05) were determined by nonparametric analyses for gMB indices and parametric analyses for all other variables were reported as mean ± standard deviation and Z scores for compared groups. Results: All subjects acclimated, but W were more resilient to HTT pre and postHA (preHA TT39.5: 29.14±7.14min (M), 35.02±3.67min (W), p=0.042; postHA TT39.5: 31.11±5.61min (M), 38.13±3.14min (W), p&lt;0.01). gMB changes were observed among all subjects with reductions in Peptostreptococcaceae and Proteobacteria at postHA (vs. preHA, p&lt;0.05). Comparison of W and M revealed marked differences. M had lower (vs. W) Christensenella (Z=-2.119, p=0.034), Erysipelotrichaceae (Z=-2.495, p=0.013) and higher Lactococcus (Z=-2.254, p=0.024), Peptostreptococcaceae (Z=-2.386, p=0.017), Pasteurellaceae(Z=-2.210, p=0.027), and Haemophilus (Z=-2.210, p=0.027) preHA. PostHA, M had lower (v. W) Eggerthella (Z=-2.022, p=0.043), Family XIII (Z=-2.025, p=0.043), Erysipelotrichaceae (Z=-2.061, p=0.039), Oxalobacteraceae (Z=-2.445, p=0.014), and higher Peptostreptococcaceae (Z=-2.173, p=0.030) with no differences in Shannon Index. Biomarkers IL-1β and IFN-γ were increased postHA (v. preHA, p&lt;0.05), but W had distinct I-FABP (decreased v. M, p&lt;0.05) and IFN-γ (increased v. M, p&lt;0.05) responses. Conclusion: gMB changes during heat acclimation include bacteria associated with heat stress responses in previous literature. W and M differ in gMB, acute heat tolerance, and acclimation responses with concomitant sex differences in inflammatory and metabolite markers potentially related to gMB. Ongoing research investigates associations of targets such as Proteobacteria with previous findings related to heat tolerance and acclimation and metabolite patterns in systemic circulation associated with bacterial species significantly affected by HA. DoD BA200299. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparison of Transcriptomic Changes in Survivors of Exertional Heat Illness with Malignant Hyperthermia Susceptible Patients.

Exertional heat illness (EHI) is an occupational health hazard for athletes and military personnel-characterised by the inability to thermoregulate during exercise. The ability to thermoregulate can be studied using a standardised heat tolerance test (HTT) developed by The Institute of Naval Medicine. In this study, we investigated whole blood gene expression (at baseline, 2 h post-HTT and 24 h post-HTT) in male subjects with either a history of EHI or known susceptibility to malignant hyperthermia (MHS): a pharmacogenetic condition with similar clinical phenotype. Compared to healthy controls at baseline, 291 genes were differentially expressed in the EHI cohort, with functional enrichment in inflammatory response genes (up to a four-fold increase). In contrast, the MHS cohort featured 1019 differentially expressed genes with significant down-regulation of genes associated with oxidative phosphorylation (OXPHOS). A number of differentially expressed genes in the inflammation and OXPHOS pathways overlapped between the EHI and MHS subjects, indicating a common underlying pathophysiology. Transcriptome profiles between subjects who passed and failed the HTT (based on whether they achieved a plateau in core temperature or not, respectively) were not discernable at baseline, and HTT was shown to elevate inflammatory response gene expression across all clinical phenotypes.

Heat Intolerance, Body Size, and Return to Duty.

BACKGROUND: Exertional heatstroke affects athletes and soldiers and can lead to temporary heat intolerance. The heat tolerance test (HTT) was developed to assist in the return-to-duty decisions of military personnel. Although there are several possible causes for heat intolerance, a soldier who fails the test is prevented from returning to serve in a front-line combat unit, regardless of the underlying reason.CASE REPORT: A 19-yr-old special infantry male soldier with unremarkable medical history collapsed during an afternoon hand-to-hand combat training session in the gym. The medic on site promptly initiated inefficient tap water cooling and measured a rectal temperature of 38.7 °C; he returned to duty the same evening. A few weeks later, after intensive physical training, he experienced exhaustion during a stretcher-carrying foot march. He was referred by the unit's physician, who suspected a condition of heat intolerance, to an HTT. The soldier underwent two HTTs, which were found to be positive. Consequently, he was discharged from serving in his infantry unit. No congenital or functional underlying causes could explain the diagnosis of heat intolerance.DISCUSSION: We discuss the possibility that the only explaining cause for the two positive HTTs was the soldier's anthropometric measures, particularly the low body surface area to body weight ratio. We raise the question of whether this soldier could have been returned safely to duty.Rabotin A, Epstein Y, Ketko I. Heat intolerance, body size, and return to duty. Aerosp Med Hum Perform. 2023; 94(7):546-549.

Sensitivity and specificity of using exercise heart rate in a thermoneutral environment to predict heat tolerance status.

Following heat illness, a return to activity may require passing a heat tolerance test (HTT). However, there are several logistical limitations to the widespread use of the HTT. Thus, it would be advantageous to develop a test that could be conducted in a thermoneutral (~22°C) environment to predict heat tolerance status. The purpose of the current study was to determine the sensitivity and specificity of using the criteria of a heart rate (HR) ≥130 bpm following 30 min of thermoneutral exercise in detecting heat-intolerant and heat-tolerant individuals. Sixty-five subjects visited the lab on 3 separate days. The first visit consisted of completing a maximal oxygen uptake (VO2 max) test to assess cardiovascular fitness. For lab visits 2 and 3, subjects randomly completed a 2-hour walking treadmill test in either a hot (40°C, 40% relative humidity [RH]) or thermoneutral (22°C, 40% RH) environment. Forty-eight subjects were classified as heat-intolerant and 17 subjects as heat-tolerant. Using the criterion of a HR ≥130 bpm at 30 min of exercise in the thermoneutral environment, specificity (54%) and sensitivity (100%) of passing the HTT was calculated. Secondary analysis using multiple regression revealed 3 significant variables for predicting ending HR during the HTT. They were: 1) absolute VO2 max (l/min), 2) age, and 3) HR at 30 min of exercise during thermoneutral exercise. Exercise in a thermoneutral environment had a positive predictive value of 100%, thus, if a subject has a HR ≥130 bpm at 30 min of exercise in a thermoneutral environment, they are very likely to fail a subsequent 2-hour HTT in the heat and be classified as heat-intolerant. Therefore, prior screening has the potential to save time and money, along with providing safety to a heat-intolerant subject. Int J Occup Med Environ Health. 2023;36(2):192-200.

Site-specific tissue lipolysis and fat metabolism differs between men and women during a treadmill-based heat tolerance test without differences in circulating biomarkers

Purpose: To test the hypothesis that measures of lipid metabolism and substrate utilization differ between men and women exposed to extreme exercise-heat stress. Methods: Physically active men (n=6, 30±8 yrs, 78.8±11.0 kg, body fat 19.4±9.8%, VO2max 49.9±2.9 mL -1· kg -1· min -1 ) and women (n=6, 25±3 yrs, 60.6±4.1 kg, 25.2±6.8%, 46.3±4.5mL -1· kg -1· min -1 ) completed a treadmill-based heat tolerance test (HTT) (2 hours, 3.1 mph, 2% grade in extreme environmental conditions (104°F, 40% relative humidity). Differences (pre-, post-, change, percentage change, mean difference (MD)) within and between groups were analyzed with nonparametric inferential statistical tests. Subcutaneous abdominal adipose tissue (SCAAT) interstitial glycerol concentration and adipose tissue blood flow (i.e., ethanol Output: Input (O:I)) pre-exercise, every 30 minutes (min) of exercise, and during recovery was measured with microdialysis and assay of biofluids. Circulating concentrations of non-esterified fatty acids (NEFAs), insulin, insulin-like growth factor (IGF-1), epinephrine (EPI), and norepinephrine (NE), and cortisol were measured with commercially available kits. Resting energy expenditure (REE) was measured pre- and post-exercise using a metabolic cart. Exercising substrate utilization and metabolic heat production (MHP) were collected during 30 and 90 mins of the HTT. Results: Despite no sex differences in markers associated with stress-related metabolic signaling (cortisol, EPI, NE), endocrine response (IGF-1, insulin), or systemic concentrations of NEFAs, fat oxidation (g·min -1 ) was higher in men (vs. women) at 30 min of HTT (men (M), women (W): 0.56±0.03, 0.45±0.05, p=0.005) and at 90 min of HTT (0.61±0.05, 0.48±0.12, p=0.05). SCAAT interstitial glycerol and O:I were similar across all time points between sexes (baseline glycerol ranges (mmol·L -1 ): 92.8-530.7 (W), 321.8-588.8 (M); O:I ratio ranges: 0.42-0.79 (W), 0.55-0.77 (M). However, women had significantly greater percent change in interstitial glycerol concentration from baseline (vs. M) (W vs. M: 275 ± 287.56% vs. -8.69 ± 32.41%, p=0.003). Pre- and post-exercise REE were 16.9% (MD:371.6 kcal·day -1 , p=0.003) and 15.5% (MD:343.5kcal·day -1 , p=0.050) lower in W compared to M. Mean MHP was higher in men (MD 85W). Conclusion: Fat oxidation and SCAAT lipolysis rates were higher in men vs. women after an acute bout of strenuous exercise-heat stress. Ongoing analyses are investigating sex, energy expenditure, and heat production contributions to differences between men and women observed in our study. Our findings suggest potential for sex-specific dietary recommendations during stress exposures. DoD BA200299, HRPO E02882.1a This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Development of a screening tool for assessment of climate change-related heat illness in the clinical setting.

Extreme heat contributes to heat-related illnesses resulting from heat intolerance, which is the inability to maintain a thermal balance to tolerate heat stress. In the United States, heat-related mortality for older persons has almost doubled in the past 20 years. Other populations at risk for heat-related illness (HRI) include children, pregnant people, those who work outside, young people participating in outdoor sports, and at-risk populations such as Black, indigenous, and populations of color. The classic heat tolerance test used for decades monitoring physiological responses to repetitive motions is impractical across large and potentially health challenged populations and does not identify environmental or social factors or specific vulnerable populations. To address this issue, we developed a heat-related illness screening tool (HIST) to identify individuals at risk for HRI morbidity and mortality based on their physical, environmental, and social vulnerabilities with an emphasis on populations of concern. The HIST has the potential to be used as routine clinical screening in the same way as other commonly used screening tools. Heat intolerance affects patient outcomes and quality of life; therefore, early screening with a simple, easy-to-administer screening tool such as the HIST can identify people at risk and refer them to services that address heat exposure and/or create safety nets to prevent heat-related illnesses.

Identification of global transcriptional variations in human PBMCs two months post heat injury helps categorization heat tolerant or heat intolerant phenotypes.

Thermal intolerance may limit activity in hostile environments. Following heat illness two physiologically distinct phenotypes evolve: Heat Tolerant (HT) and Heat Intolerant (HI). The recognition that heat illness alters gene expression justified revisiting the established physiological concept of HI. We used a DNA microarray to examine the global transcriptional response in Peripheral Blood Mononuclear Cells (PMBCs) from HI and HT phenotypes, categorized 2-mo post heat injury using a functional physiological Heat Tolerance Test (HTT, 40°C)-Recovery (R, 24°C) protocol. The impact of recurrent heat stress was studied in vitro using PBMCs from controls (participants with no history of heat injury), HI and HT (categorized by functional HTT) with a customized NanoString array. There were significant differences under basal conditions between the HI and HT. HI were more immunological alerted. Almost no shared genes were found between end-HTT and recovery phases, suggesting vast cellular plasticity. In HI, mitochondrial function was dysregulated, canonical pathways associated with exercise endurance-NRF2 and insulin were downregulated, while AMPK and PPAR were upregulated. HT exhibited reciprocal responses, suggesting that energy dysregulation found in HI interfered with performance in the heat. The endoplasmic-reticulum stress response was also suppressed in HI. In vitro HTT (43°C) abolished differences between HI and HT PBMCs including the HSPs genes, while controls showed profound HSPs upregulation.

Alteration of gut microbiota after heat acclimation may reduce organ damage by regulating immune factors during heat stress.

Heat-related illnesses can lead to morbidity, which are anticipated to increase frequency with predictions of increased global surface temperatures and extreme weather events. Although heat acclimation training (HAT) could prevent heat-related diseases, the mechanisms underlying HAT-promoting beneficial changes in organ function, immunity, and gut microbes remain unclear. In the current study, we recruited 32 healthy young soldiers and randomly divided them into 4 teams to conduct HATs for 10 days: the equipment-assisted training team at high temperature (HE); the equipment-assisted training team under normal hot weather (NE); the high-intensity interval training team at high temperature (HIIT), and the control team without training. A standard heat tolerance test (HTT) was conducted before (HTT-1st) and after (HTT-2nd) the training to judge whether the participants met the heat acclimation (HA) criteria. We found that the participants in both HE and NE teams had significantly higher acclimation rates (HA/total population) than whom in the HIIT team. The effects of HAT on the participants of the HE team outperformed that of the NE team. In the HA group, the differences of physiological indicators and plasma organ damage biomarkers (ALT, ALP, creatinine, LDH, α-HBDH and cholinesterase) before and after HTT-2nd were significantly reduced to those during HTT-1st, but the differences of immune factors (IL-10, IL-6, CXCL2, CCL4, CCL5, and CCL11) elevated. The composition, metabolism, and pathogenicity of gut microbes changed significantly, with a decreased proportion of potentially pathogenic bacteria (Escherichia-Shigella and Lactococcus) and increased probiotics (Dorea, Blautia, and Lactobacillus) in the HA group. Training for a longer time in a high temperature and humidity showed beneficial effects for intestinal probiotics. These findings revealed that pathogenic gut bacteria decrease while probiotics increase following HA, with elevated immune factors and reduced organ damage during heat stress, thereby improving the body's heat adaption.

Growth and yield performances, pathogenicity, heat tolerance, antioxidant activity, and pungency level of anthracnose resistant and heat tolerant inbreed lines and their F1 hybrids of chili (Capsicum annuum L.)

Chili pepper (Capsicum annuum L.) cultivation is hampered by biotic and abiotic stressors, with poor performance caused by high temperatures exceeding 42 °C and anthracnose infestation. Chemical constituents such as antioxidants, phenols, capsaicin, and dihydrocapsaicin have a relationship with biotic and abiotic tolerance or resistance. Experiment was conducted with anthracnose resistant (CP-36, DP-37, DP-57, AP-25 and BP-23), heat tolerant inbreed lines (Putra chili 1, Putra chili 4, Putra chili 7, Putra chili 9 and Putra chili 10) and their hybrids to find anthracnose-resistant, heat-tolerant chili genotypes with high yield and pungency levels. For this purposes, pathogens were injected into both unripe and ripe chili fruits to determine their pathogenicity. On the other hand, four-week-old seedling was raised for a heat tolerance test to determine the percentage of partial damage (%) and thermo-stability index of the cell membrane (%). The research also included morphological, yield and yield contributing, physiological, and biochemical assessment in order to identify superior chili hybrids. All growth, yield, and physiological traits showed excellent genetic progress and heritability, but correlation analysis showed a highly significant positive link between yield per plant, plant height, the total number of branches, and the number of fruits per plant. Lesion area of unripe fruits were varied from 0.00 (cm2) to 0.24 (cm2) and 0.00 (cm2) to 0.18 (cm2) for the pathogen, UPMC1191 (Colletotrichum fructicola) and UPMC1192 (Colletotrichum sojae), respectively and also indicated that differential resistant to anthracnose pathogen. In a heat tolerance test, all of the hybrids with the improved heat tolerant line performed better in terms of cell membrane thermo-stability, partial damage at various temperature gradients, and canopy temperature depression. In terms of biochemical state, DP-37 × Putra chili 7; AP-25 × Putra chili 10 had a moderate level of pungency, while some other parents and hybrids had mild level of pungency. After screening with Colletotrichum pathogen, heat tolerance test, biochemical constitute and yield performance, following hybrids would be better for commercial production to meet up the demand such as CP-36 × Putra chili 1; CP-36 × Putra chili 7; CP-36 × Putra chili 9; DP-37 × Putra chili 1; DP-37 × Putra chili 10; DP-37 × Putra chili 4; DP-37 × Putra chili 7; DP-37× Putra chili 9; DP-57 × Putra chili 7; DP-57 × Putra chili 9; DP-57 × Putra chili 10; AP-25 × Putra chili 9; AP-25 × Putra chili 4; BP-23 × Putra chili 7; BP-23 × Putra chili 9; BP-23 × Putra chili 1 and would be use in future chili breeding program.

Cognitive Assessment During Heat Tolerance Test (HTT)

According to the Israel Defense Forces (IDF) regulations every soldier who had suffered an exertional heat injury (EHI) while exercising during military training, in varying degrees of severity, from heat exhaustion to heatstroke had to take the heat tolerance test (HTT) as part of clearance for back to duty. The criteria to determine the tolerance to heat are based solely on physiological parameters, while no cognitive evaluation is considered in the HTT. PURPOSE: To evaluate the correlation and the role of cognitive assessment and mood state with the physiological parameters monitored during the HTT. METHODS: Eighty five post EHI subjects, performed the IDF HTT (treadmill: 5km/h 2% elevation at 40C 40%). Subjects were continuously monitored for body core and skin temperatures, heart rate and sweat rate. Before, during (60 min.) and at the end of the HTT (120 min.) all participants took voluntarily a psychomotor vigilance test (PVT), which consisted of visual reaction time test using a laptop (cognitive assessment), and filled the profile of mood states (POMS) questionnaire (mood state assessment). RESULTS: According to the physiological criteria 66 subjects were diagnosed as heat tolerant (HT) and 19 as heat intolerant (HI). Analysis of the POMS revealed, in the different criteria, a lower mood for the HI individuals (p<0.01). PVT resulted with longer reaction time in the HI group (p<0.01). CONCLUSION: The adverse effects of heat stress on cognitive performance and mood state during HTT was lower for HT than HI subjects. Cognitive assessment during HTT can be used as an auxiliary tool in the HTT.

Dynamics of Thermolysis and Skin Microstructure in Water Buffaloes Reared in Humid Tropical Climate-A Microscopic and Thermographic Study.

The thermolytic capacity test is used to assess the adaptability of animals to existing environmental conditions. However, there is insufficient information on the relationship between histomorphometry and adaptability of buffaloes. Thus, this study aimed to assess the use of thermolysis pathways by buffaloes reared in a hot and humid environment so as to understand the relationships between environment, skin morphological characteristics, and heat storage, as well as the intensity and proportionality of use of its ways of dissipating heat to maintain homeothermy. The heat tolerance test, associated with the evaluations via infrared thermography, was applied to 10 female Murrah buffaloes and tegument histomorphometry was carried out. The animals exhibited very high heat tolerance with an average of 9.66 ± 0.21 and used thermal polypnea as the main heat dissipation pathway. Their mean skin thickness was 6.03 ± 1.16 mm and the active sweat and sebaceous gland tissue were 1.57 ± 0.38% and 1.08 ± 0.39%, respectively. The buffaloes exhibited a positive correlation between eyeball temperature and internal body temperature (r = 0.84523, p < 0.0001) and a negative correlation between respiratory rate and skin thickness (r = −0.73371, p = 0.0157). The high thermolytic capacity in shade conditions confirms the importance of access to shade in buffalo rearing systems in tropical regions.

Evaluation of various phenotypic methods for differentiation of Candida dubliniensis from Candida albicans

IntroductionCandida dubliniensis was first identified by Sullivan et al. (1995) in Dublin, Ireland. Its clinical significance is associated with development of fluconazole-resistance and invasive diseases in immunocompromised hosts. C. dubliniensis share many features with C. albicans so has been overlooked and misidentified for a long time. AimsEvaluation of various phenotypic tests with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) as a gold standard to find out the best method/methods for identifying C. dubliniensis. Materials and methodsFirst PCR-RFLP was performed on 186C. albicans and 14C. dubliniensis strains and then five phenotypic tests were performed simultaneously on all the strains. ResultsThe results of salt tolerance test at 48 h, colony color on HiCrome candida differential agar (HCDA) at 72 h, heat tolerance test at 48 h, xylose assimilation using discs at 72 h and growth on xylose based agar medium (XAM) at 48 h are completely concordant with PCR-RFLP. Colony color on Tobacco agar could differentiate accurately 100% test strains while peripheral hyphal fringes and chlamydosporulation on this agar was seen in only 86% and 87% respectively. Our routine methods proved to be cost effective than PCR-RFLP but the turnaround time was same or more than PCR-RFLP. ConclusionFor routine identification of C. dubliniensis we recommend use of colony color on HCDA and growth on XAM as simple, reliable and inexpensive method.

Haematological, Biochemical and Hormonal Biomarkers of Heat Intolerance in Military Personnel.

Simple SummaryThis study focuses on the biomarkers that are predictive of heat intolerance in military populations. Military personnel are at risk of exertional heat stroke when the body’s temperature increases during intense physical activity in hot weather. Exertional heat stroke (EHS) may accompany or precede heat intolerance, an unusual sensitivity to heat. However, it is unknown if blood biomarkers (haematological, biochemical and hormonal) are predictive of heat intolerance. We subjected a sample of Australian Defence Force personnel and civilian volunteers to a heat tolerance test (HTT), and blood samples were obtained pre-and post–HTT. The results showed that a history of EHS was associated with changes in creatinine and urea. The biochemical and hormonal biomarkers associated with heat intolerance were alanine amino transaminase, creatine kinase, cortisol and creatinine. Furthermore, creatinine and cortisol were identified as predictors and useful biomarkers of heat intolerance. This study also highlights the need for further exploration of genetic biomarkers to aid early identification and the return to duty process for military personnel who may be at risk of heat intolerance.Heat intolerance is the inability to withstand heat stress and this may occur due to exertional heat stroke (EHS). However, it is unknown if heat intolerance is associated with immune and hormonal disturbances. This study investigates haematological, biochemical and hormonal biomarkers related to heat intolerance and EHS in military and civilian volunteers. A quasi-experimental pre-and post-test design was used, with participants drawn from the Australian Defence Force (ADF) and the general populace. Blood samples were collected and analysed for biomarkers. Inferential statistics compared the biomarkers between the groups. Changes in alanine amino transaminase (p = 0.034), creatine kinase (0.044), cortisol (p = 0.041) and creatinine (p < 0.001) differed between the heat-intolerant and heat-tolerant groups. Participants with a history of EHS showed significant changes in creatinine (p = 0.022) and urea (p = 0.0031) compared to those without EHS history. Predictors of heat intolerance were increasing post-HTT creatinine and cortisol (OR = 1.177, p = 0.011 and OR = 1.015, p = 0.003 respectively). Conclusively, EHS history is associated with changes in creatinine and urea concentrations, while the predictors of heat intolerance are creatinine and cortisol. However, further exploration of other biomarkers, such as genetic polymorphism, is needed.

Freezing and Heating Tolerance of Pinus nigra Seedlings from Three South to North Balkan Provenances

To meet the restoration and reforestation goals in the changing environment, the translocation of genotypes and species northward and upward need to be considered to a great extent. Pinus nigra is a genetically diverse, drought sensitive species, with cold hardiness comparable to other tree species under the same climatic conditions. This study tested frost hardiness (whole plant freezing test—WPFT, and electric conductivity—EC test), and heat tolerance (heat tolerance test) of P. nigra seedlings from two southern Greek provenances (Kalamata and Grevena) and one northern Serbian provenance (Šargan) to better understand the potential of seed transfer from the south to the north of the species distribution in the Balkan peninsula. The results showed that, that for all studied provenances, the damage was great; the index of injury (Ii) at −18 °C was ranged from 49 to 54.5 (measured by the EC method) and the percentage of injured tissues ranged from 80–90% (measured by visual observation). For all studied provenances, a sharp increase in damages was observed with the fall of temperature from −5 and −18 °C and the time after exposure. The WPFT results showed that the highest tolerance to freezing (−18 °C) was presented by seedlings from the northern (Šargan) provenance; however, no significant differences were statistically detected among the studied provenances. The heat and drought-treated seedlings, from both provenances, presented significantly highler foliar damages than only drought-treated ones. For seedlings from both contrasting provenances (Grevena and Šargan), exposure to moderate heat (45 °C) and short drought did present damages but without significant difference between them. Considering freezing and heating tolerance, Greek provenances of P. nigra (i.e., Grevena region) can be successfully used in Serbian forestation and restoration programs. The present study makes a contribution towards P. nigra reforestation with practical implications for abiotic stress (frost, heat drought) tolerance among southern and northern provenances and could be valuable to determine the suitable provenances for reforestation programs and assisted population migration under climatic change scenarios.

Procedure for assessing patients referred to the UK’s military Heat Illness Clinic: a case series

IntroductionThe UK military operates a Heat Illness Clinic (HIC) to aid the return to exercise, training and occupational duty recommendations for individuals who have suffered exertional heat illness or heatstroke....