Exercise-heat Stress Research Articles

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.

Effect Of Beverage Temperature On The Relation Between Perceptual And Physiological Strain During Exercise-heat Stress

Effect Of Beverage Temperature On The Relation Between Perceptual And Physiological Strain During Exercise-heat Stress

The Effect Of Sleep Deprivation On Thermoregulation In Older Adults During Exercise-Heat Stress

The Effect Of Sleep Deprivation On Thermoregulation In Older Adults During Exercise-Heat Stress

The repeatability of a cycling exercise-heat stress test in a male population

IntroductionThere is considerable inter-individual variability in the physiological responses to environmental stressors and so to accurately assess and monitor changes in an individual's ability to cope with exercise-heat stress, a reliable protocol is required. The aim of this study was to examine the repeatability of a 90-min steady-state heat exercise bout with physiological and subjective variables, and performance during an incremental test to exhaustion post 90-min steady-state exercise. MethodSixteen mixed ability males (Age: 39 ± 15yrs; Height: 176.5 ± 4.8 cm; BM: 79.7 ± 10.3 kg; V˙O2peak: 46.2 ± 8.6 ml/kg/min; PPO: 309 ± 39W) who trained at least three times a week undertook two 90-min steady-state – followed by an incremental protocol to exhaustion – cycling heat stress tests (HSTs) in a hot-humid environment (35 °C, 60%RH). Heart rate (HR), rectal (T‾re) and skin temperature (T‾sk), rating of perceived exertion (RPE), thermal sensation (TS), and thermal comfort (TC) were measured throughout. Data was analysed using Intraclass Correlation Coefficients (ICC), technical error of measurement (TEM), Bland-Altman plots, t-tests, and Cohen's d to indicate magnitude of change. ResultsPhysiological variables indicated good repeatability evident through moderate to strong ICC ratings, low magnitudes of change (d), lower mean biases compared to their respective calculated TEMs, and statistical non-significance, except HR90, ₸sk90, and ₸sk. Hydration status showed good repeatability except for urine osmolality (osmu90) and resting urine colour (colu). Perceptual variables showed encouraging repeatability apart from resting TS and mean TS. Performance data showed good repeatability overall, however 11 participants progressed to the incremental test to exhaustion in the second visit compared to 7 in the first. ConclusionCurrent data demonstrated favourable physiological, perceptual, and performance repeatability during repeated cycling HSTs in hot-humid conditions. However, given more participants progressed to the incremental trial to exhaustion protocol in the second visit, at least one familiarisation trial may improve the reliability of exercise capacity assessment.

Mild dehydration does not alter acute changes in sweat electrolyte concentrations during exercise.

The purpose of this study was to determine the effect of hydration status on the change in sweat sodium (Na+), chloride (Cl-), and potassium (K+) concentrations during exercise-heat stress. Fifteen subjects (Six female, nine male; 29 ± 9 y; 71 ± 14 kg) completed 90 min of cycling (81% HRmax) in the heat (~33°C, 42% rh) with fluid replacement to maintain euhydration (EUH) or without fluid to dehydrate to 2.4 ± 0.4% body mass loss (DEH). Sweat was collected from the forehead (FH), right scapula (SCAP), and left (LVFA) and right (RVFA) ventral forearms using the absorbent pad technique at the beginning (0-30 min) and end of exercise (60-90 min). Sweat was analyzed for Na+, Cl-, and K+ concentrations using ion chromatography. Data are reported as mean ± SD or median ± IQR. There were no differences (Paired t-tests or Wilcoxon signed-rank tests) between EUH and DEH in the change in sweat Na+ (FH: 24.3 ± 21.5 vs. 30.8 ± 22.4 mmol/L; SCAP: 9.7 ± 6.2 vs. 9.6 ± 8.2 mmol/L; LVFA: 7.5 ± 6.0 vs. 5.6 ± 5.9 mmol/L; RVFA: 8.2 ± 8.6 vs. 7.8 ± 5.2 mmol/L), sweat Cl-, or sweat K+ at any site (p = 0.07-0.99). The change in sweat electrolyte concentrations during 90 min of exercise in the heat was not significantly influenced by mild dehydration in recreational to moderately-trained male and female athletes.

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.

Effects of two external cooling strategies on physiological and perceptual responses of athletes with tetraplegia during and after exercise in the heat

Athletes with tetraplegia may experience marked hyperthermia while exercising under environmental heat stress due to their limited ability to dissipate heat through evaporative means. This study investigated the effectiveness of two external cooling strategies (i.e., spraying water onto the body surface or using a cooling vest) on physiological and perceptual variables in tetraplegic athletes during and after an aerobic exercise session in a hot environment. Nine male wheelchair rugby players performed an incremental test to determine their maximum aerobic power output. After that, they were subjected to three experimental trials in a counter-balanced order: control (CON, no body cooling), cooling vest (CV), and water spraying (WS). During these trials, they performed 30 min of a submaximal exercise (at 65% of their maximum aerobic power) inside an environmental chamber set to maintain the dry-bulb temperature at 32 °C. The following variables were recorded at regular intervals during the exercise and for an additional 30 min following the exertion (i.e., post-exercise recovery) with the participants also exposed to 32 °C: body core temperature (TCORE), skin temperature (TSKIN), heart rate (HR), rating of perceived exertion (RPE), thermal comfort (TC), and thermal sensation (TS). While exercising in CON conditions, the tetraplegic athletes had the expected increases in TCORE, TSKIN, HR, RPE, and TC and TS scores. HR, TC, and TS decreased gradually toward pre-exercise values after the exercise, whereas TCORE and TSKIN remained stable at higher values. Using a cooling vest decreased the temperature measured only on the chest and reduced the scores of RPE, TC, and TS during and after exercise but did not influence the other physiological responses of the tetraplegic athletes. In contrast, spraying water onto the athletes' body surface attenuated the exercise-induced increase in TSKIN, led to lower HR values during recovery, and was also associated with better perception during and after exercise. We conclude that water spraying is more effective than the cooling vest in attenuating physiological strain induced by exercise-heat stress. However, although both external cooling strategies do not influence exercise hyperthermia, they improve the athletes’ thermal perception and reduce perceived exertion.

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.

Sex Differences In Energy Expenditure, Metabolic Heat, And Substrate Utilization During Exercise-Heat Stress

Purpose: To understand the influence of repeated heat exposures and biological sex on metabolic outcomes surrounding heat acclimation (HA). Based on previous data, we hypothesized that repeated heat exposures would result in higher resting caloric expenditure and exercising metabolic heat production in men (vs. women). Methods: Twenty participants (65% men, 22±3 yrs, 70.1±13.7 kg, VO2max 49.9±6.8 mL·kg −1·min −1) had 8 daily exercise-heat sessions (40°C, 40%rh, at least 60min) including heat tolerance tests (HTT; 120 min, 3.1 mph, 2% grade) on days 1 and 8. Resting energy expenditure (REE) and respiratory exchange ratio (RER) were assessed pre- and post-HTT on days 1 and 8. Metabolic heat production (MHP) and RER were collected during the HTT. Data are presented as mean difference (MD) (95% confidence intervals). For REE and RER, a 2x2 ANOVA compared metrics before HTT vs. after HTT session, pre-HA vs. post HA with sex as a between-subjects factor. For MHP and RER during exercise, a dependent samples t-test compared pre-HA vs. post-HA and independent samples t-test compared sexes pre-HA vs. post-HA. Results: Pre-HA: RER was higher before vs. after the HTT (MD:0.07 (0.05,0.09) A.U., p&lt;0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p&gt;0.05) overall, but males had higher REE before HTT (MD:564 (291,836) kcal·day −1, p&lt;0.001) and after HTT (MD:666 (395,938) kcal·day −1, p&lt;0.001) than women. Post-HA: RER was higher before vs. after the HTT (MD:0.08 (0.06,0.10) A.U., p&lt;0.001) overall with no difference between sexes. REE was not different before vs. after the HTT (p&gt;0.05), but males had higher REE before (MD:581 (328,834) kcal·day −1, p&lt;0.001) and after HTT (MD:617 (411,823) kcal·day −1, p&lt;0.001) compared to women. Comparing HA Status: RER was not different between HA status before or after the HTT (p&gt;0.05). REE was not different between HA status before the HTT (p&gt;0.05). After HTT, REE was greater pre-HA compared to post-HA (MD:142 (26,259) kcal·day −1, p=0.019). During activity, MHP was greater pre-HA compared to post-HA (MD:14 (-2,31) W/m2, p=0.042); RER was not different (p&gt;0.05). Pre-HA there were no differences in MHP or RER between sexes (p&gt;0.05); post-HA, men had greater MHP than women (MD:36 (3,67) W/m2, p=0.016); there were no sex differences in RER. Conclusion: Men exhibited greater REE than women at each time point under both conditions and men produced more metabolic heat following HA. In response to completing 8 heat exposures as part of a HA protocol, men and women differed in caloric expenditure and MHP, but not in substrate utilization. Thus, our findings provide supporting evidence for sex-specific nutritional recommendations surrounding exercise-heat stress. Funding Source: 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 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.

Sex-Specific Transcriptome Responses in Circulating Immune Cells During Exercise-Heat Stress and Acclimation

Objective: To examine the sex-based differences in heat stress and acclimation we used transcriptomic analysis to test the hypotheses that 1) gene expression varies by biological sex before and after acute heat exposure and 2) circulating immune cell transcriptome responses differ between naïve and acclimated state. Methods: Participants (3F/3M, VO2max &gt;40/45 ml×kg×min−1) completed two heat tolerance tests (HTT), termed HTT1 (120min walking at 1.39 m/s at 2% grade) and HTT2 (~70% vVO2max until rectal temperature (Trec) reached 39.5°C) before and after a 5-day heat acclimation (HA1-5, daily 60min run/jog at Trec 38.5-39.5°C), in a hot environment (40°C, 40%RH). Blood was collected in PAXgene blood RNA tubes PRE and POST HTT1, HTT2, HA1, and HA5 with a recovery (REC) timepoint ~30min after HTT2. Paired end sequencing of ribodepleted total RNA from 84 samples (14 timepoints) was performed on a NovaSeq 6000 (Illumina, Inc., San Diego, CA). All samples passed quality checks with Fastp read trimming retaining 98.2% of reads with a GC content of 49.1%. HISAT2 indexed and mapped an average of 75.9M reads to GrCh38.105. Expression was quantified with htseq-counts, excluding genes with &lt;3 mapped fragments per sample resulting in 26,671 genes. Principal component analysis indicated 36% of variation could be attributed to sex. Differential expression was assessed using DESeq2's generalized linear model, applying a Benjamini-Hochberg correction with an FDR of 0.1 and an adjusted p-value threshold of 0.1. DE genes were analyzed for functional annotation and pathways. Results: In total, we detected 8611 unique DE genes composed of protein coding (6241), lncRNA (1498), and 636 pseudogenes. Males and Females exhibited significant differences in gene expression at baseline, in naïve state (PREHA) with &gt;1555 genes showing sex differences (FDR&lt;0.1). Reactome pathways differing between M and F included cytokine signaling, response, and regulation, cell senescence, cell growth and death, cell cytoskeleton and extracellular structure and innate immunity processes (p&lt;0.05). Interestingly, heat acclimation increased the responsiveness of the transcriptome while reducing the overall magnitude of the response. PREHA HTT2 had 86 DE genes at POST rising to 3170 at REC (vs. PRE, FDR&lt;0.1). While POSTHA HTT2 had 602 DE genes at POST rising to 1236 at REC (vs. PRE, FDR&lt;0.1). GO terms protein serine kinase activity, GTPase binding, and GDP binding were present at PREHA, but absent POSTHA. Conclusion: Acute exercise-heat stress induces marked changes in circulating immune cell transcriptional landscape, while acclimation reduces this response to the same challenge in an adapted state. Sex differences exist and are the subject of ongoing analyses. 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.

Pilot Study: Comparative Hsp72 Expression in Blood Plasma, Saliva, and Exosomal Fractions During Acute Heat Stress and Acclimation

Objective: To support long-term study biomonitoring during stress, we sought to establish optimized protocols for blood and saliva. Our hypotheses were that 1) stress-specific marker Hsp72 is expressed to suffcient detectable limits and responsive to rest, exercise-heat stress, and to multi-day acclimation in saliva and blood plasma and 2) Hsp72 patterns are distinct in exosome fractions vs. unprocessed whole samples. Methods: Participants (3M/3F, M: 28±4yo, VO2max 48.87±4.08mL·kg−1·min−1, F: 25±2yo, VO2max 41.17±0.74mL·kg−1·min−1) completed a 5-day heat acclimation protocol (~40°C and relative humidity ~40%, ~70% vVO2max jog to reach and maintain a rectal temperature (Trec) range of 38.5-39.5°C for 60 total min). EDTA-treated plasma was separated and a portion was used to fractionate and isolate plasma exosomes for analyses. Whole saliva was processed and fractionated to isolate saliva exosomes for analyses. Hsp72 was analyzed in samples using a high-sensitivity ELISA kit (Enzo Life Sciences). Physiological variables (heart rate (HR), Trec) were used to confirm the stress of the exercise-heat exposures. ANOVA with t-tests for comparisons were used to assess statistical significance (p&lt;0.05). Results: All subjects acclimated, represented by decreased HR (PREHA:107±11.14bpm (M), 170.33±19.50bpm (W), p=0.01) vs. POSTHA:103.67±7.57bpm (M), 140±18.68bpm (W), p=0.04) and decreased Trec post-exercise (PREHA:38.16±0.61°C (M), 39.33±0.50°C (W), p=0.06) vs. POSTHA:37.91±0.41°C (M), 38.39±0.11°C (W), p=0.12). Men and women did differ significantly (p&lt;0.05) with HR changes but were not significantly different (p&gt;0.05) in regards to Trec. Despite physiological acclimation, there were no differences in Hsp72 across time points and by sex. Hsp72 expression was detected in plasma exosomes (0.82-5.18ng·mL−1 (M), 0.48-2.22ng·mL−1 (W)) and saliva exosomes (0.45-10.09ng·mL−1 (M), 0.25-7.18ng·mL−1(W)) and there were no significant differences between men and women (p&gt;0.05) during acute exposures and acclimation, despite some differences in physiological responses. Hsp72 was significantly higher in males overall as compared to females only in saliva exosomes (3.94±3.14ng·mL−1 (M), 1.5±1.27 ng·mL−1 (F), p=0.0003). Conclusion: Subjects acclimatized physiologically without exhibiting Hsp72 changes in their blood plasma or plasma exosomes. Salivary exosomal Hsp72 may be different between men and women. Ongoing research includes validation of the exosome fraction using exosome specific protein markers in co-expression (exosome marker and Hsp72) experiments and ongoing assays of salivary biomarkers of 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.

Exercise intensity- and body region-specific differences in sweating in middle-aged-to-older men with and without type 2 diabetes.

Type 2 diabetes is associated with reduced whole-body sweating during exercise-heat stress. However, it is unclear if this impairment is related to exercise intensity and whether it occurs uniformly across body regions. We evaluated whole-body (direct calorimetry) and local (ventilated-capsule technique; chest, back, forearm, thigh) sweat rates in physically active men with type 2 diabetes (T2D; aged 59 (7) years; V̇O2peak 32.3 (7.6) mL·kg-1·min-1; n=26; HbA1c 5.1-9.1%) and without diabetes (Control; aged 61 (5) years; V̇O2peak 37.5 (5.4) mL·kg-1·min-1; n=26) during light (~40%V̇O2peak), moderate (~50%V̇O2peak), and vigorous (~65%V̇O2peak) intensity exercise (elicited by fixing metabolic heat production at ~150, 200, 250 W·m-2, respectively) in 40°C, ~17% relative humidity. Whole-body sweating was ~11% (T2D-Control mean difference [95% confidence interval]: -37 [-63, -12] g·m-2·h-1) and ~13% (-50 [-76, -25] g·m-2·h-1) lower in the T2D compared to the Control group during moderate- and vigorous- (p≤0.001), but not light-intensity exercise (-21 [-47, 4] g·m-2·h-1; p=0.128). Consequently, the diabetes-related reductions in whole-body sweat rate were 2.3 [1.6, 3.1] times greater during vigorous relative to light exercise (p<0.001). Further, these diabetes-related impairments in local sweating were region-specific during vigorous-intensity exercise (group × region interaction: p=0.024), such that the diabetes-related reduction in local sweat rate at the trunk (chest, back) was 2.4 [1.2, 3.7] times greater than that at the limbs (thigh, arm). In summary, when assessed under hot, dry conditions, diabetes-related impairments in sweating are exercise intensity-dependent and greater at the trunk compared to the limbs.

Greater hyperthermia in men with type 2 diabetes does not lead to higher serum levels of cellular stress biomarkers following exercise-heat stress.

Type 2 diabetes (T2D) is associated with worsening age-related impairments in heat loss, causing higher core temperature during exercise. We evaluated whether these thermoregulatory impairments occur with altered serum protein responses to heat stress by measuring cytoprotection, inflammation, and tissue damage biomarkers in middle-aged-to-older men (50-74 years) with (n=16) and without (n=14) T2D following exercise in 40°C. There were no changes in irisin, klotho, HSP70, sCD14, TNF-α, and IL-6, whereas NGAL (+539 pg/mL, p=0.002) and iFABP (+250 pg/mL, p<0.001) increased similarly across groups. These similar response patterns occurred despite elevated core temperature in individuals with T2D, suggesting greater heat vulnerability.

Hormonal intrauterine devices and heat exchange during exercise.

Synthetic progestins in oral contraceptives are thought to blunt heat dissipation by reducing skin blood flow and sweating. However, whether progestin-releasing intrauterine devices (IUDs) modulate heat loss during exercise-heat stress is unknown. We used direct calorimetry to measure whole-body total (dry + evaporative) heat loss in young, physically active women (mean (SD); aged 24(4)years, 39.3(5.3) ml/kg/min) with (IUD; n=19) and without (Control; n=17) IUDs in the follicular and luteal phases of the menstrual cycle during light- and moderate-intensity exercise at fixed rates of heat production (∼175 and ∼275W/m2 ) in 30°C, ∼21% relative humidity. Between-group and -phase differences were evaluated using traditional hypothesis testing and statistical equivalence testing within pre-determined bounds (±11W/m2 ; difference required to elicit a ±0.3°C difference in core temperature over 1h) in each exercise bout. Whole-body total heat loss was statistically equivalent between groups within ±11Wm-2 (IUD-Control [90% CIs]; Light: -2 [-8, 5] W/m2 , P=0.007; Moderate: 0 [-6, 6] W/m2 , P=0.002), as were dry and evaporative heat loss (P ≤ 0.023), except for evaporative heat loss during moderate-intensity exercise (equivalence: P=0.063, difference: P=0.647). Whole-body total and evaporative heat loss were not different between phases (P≥0.267), but dry heat loss was 3 [95% CIs: 1, 5] W/m2 greater in the luteal phase (P≤0.022). Despite this, all whole-body heat loss outcomes were equivalent between phases (P≤0.003). These findings expand our understanding of the factors that modulate heat exchange in women and provide valuable mechanistic insight of the role of endogenous and exogenous female sex hormones in thermoregulation. KEY POINTS: Progestin released by hormonal intrauterine devices (IUDs) may negatively impact heat dissipation during exercise by blunting skin blood flow and sweating. However, the influence of IUDs on thermoregulation has not previously been assessed. We used direct calorimetry to show that IUD users and non-users display statistically equivalent whole-body dry and evaporative heat loss, body heat storage and oesophageal temperature during moderate- and high-intensity exercise in a warm, dry environment, indicating that IUDs do not appear to compromise exercise thermoregulation. However, within IUD users and non-users, dry heat loss was increased and body heat storage and oesophageal temperature were reduced in the luteal compared to the follicular phase of the menstrual cycle, though these effects were small and unlikely to be practically meaningful. Together, these findings expand our understanding of the factors that modulate heat exchange in women and have important practical implications for the design of future studies of exercise thermoregulation.

Erratum. Sweat Mineral-Element Responses During 7h of Exercise-Heat Stress.

Erratum. Sweat Mineral-Element Responses During 7h of Exercise-Heat Stress.

Facial fanning reduces heart rate but not tolerance to a simulated hemorrhagic challenge following exercise heat stress in young healthy humans.

We investigated whether reducing face skin temperature alters arterial blood pressure control and lower body negative pressure (LBNP) tolerance after exercise heat stress. Eight subjects (1 female; age, 27 ± 9 yr) exercised at ∼63% V̇o2max until core temperature had increased ∼1.5°C before undergoing LBNP to presyncope either with fanning to return face skin temperature to baseline (Δ-5°C, Fan trial) or without (No Fan trial). LBNP tolerance was quantified as cumulative stress index (CSI; mmHg·min). Before LBNP, whole body and face skin temperatures were elevated from baseline in both trials (38.0 ± 0.5°C and 36.3 ± 0.5°C, respectively, both P < 0.001). During LBNP, face skin temperature decreased in the Fan trial (30.9 ± 1.0°C) but was unchanged in the No Fan trial (36.1 ± 0.6°C, between trials P < 0.001). Mean arterial pressure was not different between trials (P = 0.237) and was similarly reduced at presyncope in both trials (from 82 ± 7 to 67 ± 8 mmHg, P < 0.001). During LBNP, heart rate was attenuated in the Fan trial at Mid LBNP (146 ± 16 vs. 158 ± 12 beats/min, P = 0.036) and at peak heart rate (158 ± 15 vs. 170 ± 15 beats/min; P < 0.001). LBNP tolerance was not different between trials (321 ± 248 vs. 328 ± 115 mmHg·min, P = 0.851). In exercise heat-stressed individuals, lowering face skin temperature to normothermic values suppressed heart rate thereby altering cardiovascular control during a simulated hemorrhagic challenge without reducing tolerance.

Effect Of Beverage Temperature On Whole-body Heat Dissipation During Exercise-heat Stress In Older Men

Effect Of Beverage Temperature On Whole-body Heat Dissipation During Exercise-heat Stress In Older Men

Sleep Deprivation Does Not Influence Whole-body Heat Loss During Exercise-Heat Stress In Young Men

Sleep Deprivation Does Not Influence Whole-body Heat Loss During Exercise-Heat Stress In Young Men

Separate And Combined Blockades Of Adrenergic Receptors In Sweating To Exercise-heat Stress In Young Men

Separate And Combined Blockades Of Adrenergic Receptors In Sweating To Exercise-heat Stress In Young Men