Reproductive hormone influences on thermoregulation in women

Heat wave, fine particulate matter, and cardiovascular disease mortality: A time-stratified case-crossover study in Shenzhen, China

BACKGROUND

In the context of global warming, the frequency of heat wave and the concentration of fine particulate matter (PM2.5) have increased, and more people are co-exposed to air pollution and extreme heat. However, the interaction between heat wave and PM2.5 on cardiovascular disease (CVD) mortality remained largely unknown.

METHODS

We conducted a time-stratified case-crossover study of 40,169 CVD deaths in Shenzhen, China between 2013 and 2022. Meteorological data and air pollutants information were obtained based on the residential addresses from the validated grid datasets. A total of 21 heat wave definitions were constructed using various relative temperature thresholds and durations. Conditional logistic regression was used to evaluate the independent and interactive effects of exposure to heat wave and PM2.5 on CVD mortality.

RESULTS

The odds ratios (ORs) and 95 % confidence intervals (CIs) for CVD mortality associated with heat waves ranged from 1.17 (95 % CI: 1.001,1.36) to 1.91 (95 % CI: 1.42, 2.56). For every increase of 10 µg/m³ in PM2.5 exposure, the ORs (95 % CI) for CVD mortality ranged from 1.0283 (95 % CI: 1.0162, 1.0406) to 1.029 (95 % CI: 1.0169, 1.0413). There was a synergistic effect between heat wave and PM2.5 exposures on CVD mortality. It was estimated that up to 2.03 % of CVD deaths were attributable to heat wave and PM2.5 levels exceeding the interim target 4 in the World Health Organization air quality guidelines (≥ 25 μg/m3), resulting in 816 premature deaths. Females and individuals over 75 years old were vulnerable populations.

CONCLUSIONS

Heat wave and PM2.5 exposures individually and synergistically contributed to increased risks of CVD mortality. Our findings indicate that reducing exposure to both heat wave and PM2.5 may yield significant health benefits and prevent a significant portion of premature deaths from CVDs.

Skin temperature and nitric oxide in premenopausal and postmenopausal women with fibromyalgia

OBJECTIVE

This study aimed to investigate skin temperature, indicative of peripheral vascular blood flow, core body temperature and nitric oxide (NO) levels in premenopausal and postmenopausal women with fibromyalgia (FM) and controls.

METHOD

A case-control study was carried out in 32 healthy premenopausal and 52 healthy postmenopausal women and in 17 premenopausal and 53 postmenopausal women with FM. Hand skin temperature was measured using infrared thermography, tympanic and axillary temperature with an infrared thermometer, and serum NO levels using an ozone chemiluminescence-based method.

RESULTS

Tympanic temperature was higher in postmenopausal women with FM than in postmenopausal controls. Significant differences were found in all of the temperatures recorded in both hands between healthy premenopausal women and premenopausal women with FM and between postmenopausal controls and postmenopausal women with FM. No differences were found in hand temperature, axillary or tympanic temperature, or NO levels between healthy premenopausal and postmenopausal women or between premenopausal and postmenopausal women with FM.

CONCLUSION

The association between menopause and FM could be responsible for the higher tympanic temperature observed in women with FM. FM, but not menopause, may increase hand skin temperature, which could be indicative of excessive peripheral vasodilation. Menopause may not alter body temperature or NO levels in either patients with FM or healthy women.

The impact of diurnal temperature range on the risk of hospitalizations in a low-income setting: the case of the Central Coast of Vietnam

The study aims to evaluate the effects of diurnal temperature range (DTR) on all causes, cardiovascular and respiratory conditions in the Central Coast of Vietnam, a tropical, low-income region with high DTR exposure but limited research. Daily hospital admission data from the largest hospitals in three provinces were analyzed alongside meteorological data. A time-series analysis using a generalized linear distributed lag model was conducted to examine the non-linear DTR-hospitalization association. A random-effect meta-analysis using restricted maximum likelihood was performed to calculate the pooled effects across three provinces. Stratified analyses by gender, age, season and natural disaster occurrence were conducted to identify vulnerable subpopulations. The multi-province pooled effects indicated that a 1 °C increase in DTR raised the risk of hospitalizations for all causes and respiratory diseases by 1.5% [1.2-1.8%] and 0.5% [0.0-1.0%], at lag 0-6 days. The effects of DTR on cardiovascular diseases, as well as those stratified by subgroups, were not statistically significant. Additionally, DTR had a greater adverse effect during the dry season and in the presence of natural disaster. Females and the elderly were slightly more susceptible to respiratory admissions, while males and younger individuals had a higher risk of all-cause admissions due to greater DTR effects. DTR was an independent risk factor for the exacerbation of all and specific causes, particularly among the susceptible subgroups. The findings suggested that it is necessary to take preventive measures to protect these at-risk populations from the adverse effects of extreme DTR exposure.

Menstrual cycle effects on thermoregulation while exercising in the heat

Women may be challenged to maintain thermoregulation due to hormonal changes associated with the menstrual cycle. The purpose of this study was to assess the effect of the menstrual cycle phase on core temperature, hydration status, and perceived exertion while exercising under uncompensable heat gain. Eleven eumenorrheic women (24.4 ± 1.1 yrs, 65.7 ± 2.4 kg, 22.7 ± 1.5% body fat) walked for two 180-min trials in a heat chamber (35 °C and 30% relative humidity) during early-follicular (EF) and mid-luteal (ML) phases. Subjects completed three intervals of 50 min of exercise at 50% VO2max. Physiological strain index (PSI), core temperature (TC), perceived heat (PH), and rating of perceived exertion (RPE) were measured throughout both trials. Nude body weight (NBW) and blood samples were collected pre- and post-trial. Blood samples were analyzed for hematocrit (Hct), hemoglobin (Hb), serum estrogen, progesterone, and aldosterone. NBW showed a main effect of time (p = 0.002, ηp2 = 0.62). Aldosterone showed main effect of time (p = 0.004, ηp2 = 0.59) and phase (p = 0.014, ηp2 = 0.47), peaking post exercise in both EF and ML (527.6.1 ± 89.0 pg·mL-1 vs 827.4 ± 129.5 pg mL-1 respectively, p = 0.014). Estradiol and progesterone showed main effects of phase (p = 0.007, ηp2 = 0.53; p = 0.045, ηp2 = 0.30) but not time (p = 0.68, p = 0.32). TC showed main effect of time (p < 0.001, ηp2 = 0.89) and phase, peaking at 170 min (EF: 37.8 ± 0.1 °C vs. ML: 38.0 ± 0.1 °C, p = 0.032, ηp2 = 0.38). Main effect of time was seen for PSI (p = 0.002, ηp2 = 0.88), PH (p = 0.004, ηp2 = 0.66), and RPE (p = 0.026, ηp2 = 0.80). Sweat rate, Hct, Hb, and percent dehydration were not different between the phases. In conclusion, subjects demonstrated elevated Tc and basal aldosterone in ML corresponding with elevations in estrogen and progesterone. Aldosterone significantly increased following exercise in the heat but remained elevated in ML. These results indicate that elevated Tc during ML is maintained during exercise in the heat despite similar perceived heat and effort between phases.

Impact of extreme temperature on congenital heart disease mortality: a population-based nationwide case-crossover study

Background

The association between congenital heart disease (CHD) and non-optimal temperatures has received limited investigation. We aimed to investigate the impact of extreme temperatures on CHD mortality.

Methods

We reviewed the National Mortality Surveillance System of China and retrieved death records attributable to CHD from 2013 to 2021. Temperature and air pollutants data were obtained from the ERA5-Land reanalysis dataset and the ChinaHighAirPollutants database. A two-stage case-crossover study design was implemented. Sensitivity and subgroup analyses were performed to test the robustness of findings and determine the vulnerable population.

Findings

A total of 32,168 CHD deaths were included, showing a significant association between cold and CHD mortality, while there was little effect for heat. The odd ratio (OR) ranged from 1.05 (95% confidence interval: 1.00-1.10) to 1.15 (1.03-1.29) across country, with a more pronounced impact in non-monsoon regions up to 1.67 (1.20-2.32). Cold extremes accounted for an attributable fraction of 4.09 per 1000 CHD death nationwide and 13.30 per 1000 CHD deaths in non-monsoon regions. Sensitivity analyses utilizing apparent temperature and adjusting for air pollutants confirmed the robustness of the main findings. Female and pediatric CHD patients were identified as the vulnerable population to cold extremes.

Interpretation

For the first time, this nationwide study demonstrated the significant impact of cold extremes on CHD mortality, particularly in non-monsoon regions, and among female and pediatric subgroups. These findings may suggest that healthcare professionals advise CHD patients to avoid exposure to cold extremes, and provide insight into healthcare policy adjustment.

Funding

This study was supported by the CAMS Innovation Fund for Medical Sciences (CIFMS, 2023-I2M-C&T-B-059), the Capital Health Research and Development of Special Fund (2022-1-4032) and the National High Level Hospital Research Funding (2022-GSP-GG-19).

Original salivary sex hormone data of naturally menstruating athletes and hormonal contraceptive users

Objectives

There is a lack of data on salivary sex hormones across the menstrual cycle (MC) or hormonal contraceptive (HC) cycle of elite athletes. We aimed to provide original data on salivary sex hormones (17β-estradiol, progesterone and free testosterone) in naturally menstruating female athletes with a regular cycle or irregular cycle and using combined HC. A secondary purpose was to compare these data with published data from the general population according to the menstrual status (MC or HC or irregularly menstruating).

Methods

367 saliva tests were performed on 44 elite athletes during 6 months of follow-up to certify for cycle regularity. Athletes were grouped into regular MC, n=13; irregular MC, n=5; and HC, n=26. We compared salivary data of regular MC across six cycle phases (menses, mid-follicular, late follicular, early luteal, mid-luteal and late luteal phases) with published data from women with a similar MC or HC status from the general population.

Results

We provided salivary original data according to six sub-phases among elite athletes with regular MC. HC athletes showed lower salivary sex hormonal levels, markedly after the first week of active HC compared with regular MC. Athletes with irregular cycles do not show a progesterone rise from the first half to the second half of the cycle (Δirregular=0.38 (1.90), a rise detectable within regular MC group ΔregularMC=2.86 (2.88)).

Conclusions

We provided original data for salivary sex hormone levels in elite female athletes. These references may be valuable for research investigating MC or combined HC data, particularly in longitudinal follow-ups requiring repeated measurements.

Biological rhythms in premenstrual syndrome and premenstrual dysphoric disorder: a systematic review

BACKGROUND

Women with premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PMDD) typically experience a range of psychological and physiological symptoms that negatively affect their quality of life. Disruption in biological rhythms, including alterations of the sleep-wake cycle, have been implicated in PMS/PMDD, though literature is still growing to substantiate these findings. The objective of this study is to systematically review the available literature on biological rhythms disruption in PMS/PMDD.

METHODS

A literature search was conducted on four databases (Pubmed, Embase, Medline, and Web of Science) on December 3rd, 2021. This search yielded a total of 575 articles that assessed the relationship between biological rhythms and PMS/PMDD/premenstrual symptoms.

RESULTS

After the exclusion of irrelevant articles and hand-searching references, 25 articles were included in this systematic review. Some studies showed that women with PMS/PMDD present lower melatonin levels, elevated nighttime core body temperature, and worse subjective perception of sleep quality when compared to women without PMS/PMDD. Other biological rhythms parameters showed either no differences between groups (wrist actimetry) or conflicting results (objective sleep parameters, cortisol, prolactin, and thyroid stimulating hormone).

CONCLUSION

Current research demonstrates that women with PMS/PMDD experience lower melatonin levels, higher body temperature, and worse subjective perception of sleep quality. This review outlines some possible mechanisms behind these findings and proposes recommendations for future research. This systematic review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) under registration number CRD42020149921.

Menstrual Cycle Variations in Wearable-Detected Finger Temperature and Heart Rate, But Not in Sleep Metrics, in Young and Midlife Individuals

Most studies about the menstrual cycle are laboratory-based, in small samples, with infrequent sampling, and limited to young individuals. Here, we use wearable and diary-based data to investigate menstrual phase and age effects on finger temperature, sleep, heart rate (HR), physical activity, physical symptoms, and mood. A total of 116 healthy females, without menstrual disorders, were enrolled: 67 young (18-35 years, reproductive stage) and 53 midlife (42-55 years, late reproductive to menopause transition). Over one menstrual cycle, participants wore Oura ring Gen2 to detect finger temperature, HR, heart rate variability (root mean square of successive differences between normal heartbeats [RMSSD]), steps, and sleep. They used luteinizing hormone (LH) kits and daily rated sleep, mood, and physical symptoms. A cosinor rhythm analysis was applied to detect menstrual oscillations in temperature. The effect of menstrual cycle phase and group on all other variables was assessed using hierarchical linear models. Finger temperature followed an oscillatory trend indicative of ovulatory cycles in 96 participants. In the midlife group, the temperature rhythm's mesor was higher, but period, amplitude, and number of days between menses and acrophase were similar in both groups. In those with oscillatory temperatures, HR was lowest during menses in both groups. In the young group only, RMSSD was lower in the late-luteal phase than during menses. Overall, RMSSD was lower, and number of daily steps was higher, in the midlife group. No significant menstrual cycle changes were detected in wearable-derived or self-reported measures of sleep efficiency, duration, wake-after-sleep onset, sleep onset latency, or sleep quality. Mood positivity was higher around ovulation, and physical symptoms manifested during menses. Temperature and HR changed across the menstrual cycle; however, sleep measures remained stable in these healthy young and midlife individuals. Further work should investigate over longer periods whether individual- or cluster-specific sleep changes exist, and if a buffering mechanism protects sleep from physiological changes across the menstrual cycle.

The effects of ambient temperature on non-accidental mortality in the elderly hypertensive subjects, a cohort-based study

BACKGROUND

The association between ambient temperature and mortality has yielded inconclusive results with previous studies relying on in-patient data to assess the health effects of temperature. Therefore, we aimed to estimate the effect of ambient temperature on non-accidental mortality among elderly hypertensive patients through a prospective cohort study conducted in northeastern China.

METHODS

A total of 9634 elderly hypertensive patients from the Kailuan research who participated in the baseline survey and follow-up from January 1, 2006 to December 31, 2017, were included in the study. We employed a Poisson generalized linear regression model to estimate the effects of monthly ambient temperature and temperature variations on non-accidental mortality.

RESULTS

After adjusting for meteorological parameters, the monthly mean temperature (RR = 0.989, 95% CI: 0.984-0.993, p < 0.001), minimum temperature (RR = 0.987, 95% CI: 0.983-0.992, p < 0.001) and maximum temperature (RR = 0.989, 95% CI: 0.985-0.994, p < 0.001) exhibited a negative association with an increased risk of non-accidental mortality. The presence of higher monthly temperature variation was significantly associated with an elevated risk of mortality (RR = 1.097, 95% CI:1.051-1.146, p < 0.001). Further stratified analysis revealed that these associations were more pronounced during colder months as well as among male and older individuals.

CONCLUSIONS

Decreased temperature and greater variations in ambient temperature were observed to be linked with non-accidental mortality among elderly hypertensive patients, particularly notable within aging populations and males. These understanding regarding the effects of ambient temperature on mortality holds clinical significance for appropriate treatment strategies targeting these individuals while also serving as an indicator for heightened risk of death.

Agreement between measured and self-reported physiological strain in males and females during simulated occupational heat stress

RATIONALE

Monitoring physiological strain is recommended to safeguard workers during heat exposure, but is logistically challenging. The perceptual strain index (PeSI) is a subjective estimate thought to reflect the physiological strain index (PSI) that requires no physiological monitoring. However, sex is known to influence perceptions of heat stress, potentially limiting the utility of the PeSI.

OBJECTIVES

The objective of this study was to assess whether sex modifies the relationship between PeSI and PSI.

METHODS

Thirty-four adults (15 females) walked on a treadmill (moderate intensity; ~200 W/m2) for 180 min or until termination (volitional fatigue, rectal temperature ≥39.5°C) in 16°C, 24°C, 28°C, and 32°C wet-bulb globe temperatures. Rectal temperature and heart rate were recorded to calculate PSI (0-10 scale). Rating of perceived exertion and thermal sensation were recorded to calculate PeSI (0-10 scale). Relationships between PSI and PeSI were evaluated via linear mixed models. Mean bias (95% limits of agreement [LoA]) between PSI and PeSI was assessed via Bland-Altman analysis. Mean absolute error between measures was calculated by summing absolute errors between the PeSI and the PSI and dividing by the sample size.

FINDINGS

PSI increased with PeSI (p < 0.01) but the slope of this relation was not different between males and females (p = 0.83). Mean bias between PSI and PeSI was small (-0.4 points), but the 95% LoA (-3.5 to 2.7 points) and mean absolute error were wide (1.3 points).

IMPACT

Our findings indicate that sex does not appreciably impact the agreement between the PeSI and PSI during simulated occupational heat stress. The PeSI is not a suitable surrogate for the PSI in either male or female workers.

Auditing the Representation of Females Versus Males in Heat Adaptation Research

The aim of this audit was to quantify female representation in research on heat adaptation. Using a standardized audit tool, the PubMed database was searched for heat adaptation literature from inception to February 2023. Studies were included if they investigated heat adaptation among female and male adults (≥18-50 years) who were free from noncommunicable diseases, with heat adaptation the primary or secondary outcome of interest. The number and sex of participants, athletic caliber, menstrual status, research theme, journal impact factor, Altmetric score, Field-Weighted Citation Impact, and type of heat exposure were extracted. A total of 477 studies were identified in this audit, including 7,707 participants with ∼13% of these being female. Most studies investigated male-only cohorts (∼74%, n = 5,672 males), with ∼5% (n = 360 females) including female-only cohorts. Of the 126 studies that included females, only 10% provided some evidence of appropriate methodological control to account for ovarian hormone status, with no study meeting best-practice recommendations. Of the included female participants, 40% were able to be classified to an athletic caliber, with 67% of these being allocated to Tier 2 (i.e., trained/developmental) or below. Exercise heat acclimation was the dominant method of heat exposure (437 interventions), with 21 studies investigating sex differences in exercise heat acclimation interventions. We recommend that future research on heat adaptation in female participants use methodological approaches that consider the potential impact of sexual dimorphism on study outcomes to provide evidence-based guidelines for female athletes preparing for exercise or competition in hot conditions.

Whole-body passive heating at moderate hyperthermic state impairs static and dynamic balance in healthy females

BACKGROUND

Whether static and dynamic balances can be impaired with increasing core temperature in female participants remains unknown.

PURPOSE

We tested the hypothesis that static and dynamic balances can be further impaired with systematic increases of core temperature by Δ1 °C and Δ 2 °C using whole-body passive heating.

METHOD

Eighteen female participants underwent a control trial (Con) and two progressive passive heating trials with Δ 1 °C and Δ 2 °C increase of oral temperature (TOral) using 45 °C water bath. In each trial, we assessed static balance with both eye open and closed and assessed dynamic balance using obstacle crossing at 10 %, 20 % and 30 % of the participant's leg length.

RESULTS

Static balance was not different between Con and Δ1 °C but was different between Δ1 °C and Δ 2 °C in an eye closed condition. Furthermore, Δ 2 °C greatly impaired both static and dynamic balances when compared to Con. The joint angles and toe clearance increased while leading heel-obstacle distance decreased during crossing obstacles at the height of 20 % and 30 % leg length with leading limbs in the Δ2 °C compared to Δ 1 °C and Con (All P < 0.05). However, no differences in joint kinematics and toe clearance with trailing limbs were observed (All P > 0.05).

CONCLUSION

In female participants, static and dynamic balances only became impaired when TOral increased 2 °C from baseline.

Guidelines on the use of sex and gender in cardiovascular research

In cardiovascular research, sex and gender have not typically been considered in research design and reporting until recently. This has resulted in clinical research findings from which not only all women, but also gender-diverse individuals have been excluded. The resulting dearth of data has led to a lack of sex- and gender-specific clinical guidelines and raises serious questions about evidence-based care. Basic research has also excluded considerations of sex. Including sex and/or gender as research variables not only has the potential to improve the health of society overall now, but it also provides a foundation of knowledge on which to build future advances. The goal of this guidelines article is to provide advice on best practices to include sex and gender considerations in study design, as well as data collection, analysis, and interpretation to optimally establish rigor and reproducibility needed to inform clinical decision-making and improve outcomes. In cardiovascular physiology, incorporating sex and gender is a necessary component when optimally designing and executing research plans. The guidelines serve as the first guidance on how to include sex and gender in cardiovascular research. We provide here a beginning path toward achieving this goal and improve the ability of the research community to interpret results through a sex and gender lens to enable comparison across studies and laboratories, resulting in better health for all.

Female Athletes and the Menstrual Cycle in Team Sports: Current State of Play and Considerations for Future Research

Over the past ten years there has been a dramatic rise in female sport participation and accompanying female professional national leagues across multiple sports, yet research has not followed suit. Although there are known variations between female and male physiology, training protocols in female sport are predominantly underpinned by research undertaken in male athletes. The hormonal variability experienced by women across the menstrual cycle, as well as the menstrual cycle variability between women, may contribute to the complexity of conducting rigorous physiological studies, leading to a paucity of robust sports-specific research that can be confidently applied to female athletes. Moreover, barriers exist in female sport that potentially limit the ability to conduct research, including the lack of full-time programs and limited resources. Recently, there has been increased interest in the potential effects of fluctuations in the female sex hormones, progesterone and oestrogen, on sport performance across different phases of the menstrual cycle. However, current research evaluating the menstrual cycle and physical performance (such as strength, speed, aerobic fitness, and athletes' perception of their performance) have shown inconsistent results. Additionally, methodological design across studies has shown little consistency, making it difficult to draw firm conclusions, which potentially prevents female athletes optimising their physical and sporting performance. It further impacts coaches and sports science researchers in their ability to provide appropriate training recommendations and educational opportunities. It is important to progress in female athlete research with an understanding of how the unique physiology of female athletes may influence their ability to physically perform in their respective sport, which requires representation in sports science research. This paper will provide an overview on current evidence and limitations within menstrual cycle research and provide considerations and directions for future research in this space within team sports.

Neuromuscular and gene signaling responses to passive whole-body heat stress in young adults

This study aimed to investigate whether acute passive heat stress 1) decreases muscle Maximal Voluntary Contraction (MVC); 2) increases peripheral muscle fatigue; 3) increases spinal cord excitability, and 4) increases key skeletal muscle gene signaling pathways in skeletal muscle. Examining the biological and physiological markers underlying passive heat stress will assist us in understanding the potential therapeutic benefits. MVCs, muscle fatigue, spinal cord excitability, and gene signaling were examined after control or whole body heat stress in an environmental chamber (heat; 82 °C, 10% humidity for 30 min). Heart Rate (HR), an indicator of stress response, was correlated to muscle fatigue in the heat group (R = 0.59; p < 0.05) but was not correlated to MVC, twitch potentiation, and H reflex suppression. Sixty-one genes were differentially expressed after heat (41 genes >1.5-fold induced; 20 < 0.667 fold repressed). A strong correlation emerged between the session type (control or heat) and principal components (PC1) (R = 0.82; p < 0.005). Cell Signal Transduction, Metabolism, Gene Expression and Transcription, Immune System, DNA Repair, and Metabolism of Proteins were pathway domains with the largest number of genes regulated after acute whole body heat stress. Acute whole-body heat stress may offer a physiological stimulus for people with a limited capacity to exercise.

Skin temperature of women: A prospective longitudinal study

INTRODUCTION

The different phases of a woman's life, such as the reproductive phase and menopause, are points of great hormonal oscillation, especially estrogen and progesterone, which can interfere with skin temperature.

OBJECTIVE

To describe and compare skin temperatures of women during their physiological menstrual cycle, the use of exogenous hormones and menopause over a period of 28 days.

METHOD

This is a prospective observational study using a quantitative approach. A total of 45 volunteers participated and were equally allocated into three groups: Exogenous Hormone Group (EHG), Physiological Menstrual Cycle Group (PMCG) and Menopause Group (MG). All were submitted once a week to body composition measurements over a period of 28 days using an InBody 120 bioimpedance scale, and skin temperature using a FLIR model T-360 thermographic camera.

RESULTS

No significant differences were found between the mean skin temperature of women with a physiological cycle using exogenous hormones and menopause in relation to the evaluation time or between groups. However, younger women had higher temperatures in specific skin regions, such as in the breast, lower abdomen and thigh (P < 0.05) compared to menopausal women. In addition, negative correlations were observed between body fat and skin temperature of the breasts, trunk, abdomen, upper limbs and right lower limb (P < 0.05).

CONCLUSION

It was observed that the general skin temperature of women is not altered due to exogenous hormones, menstrual cycle phase or menopause, and that skin temperature tends to be lower in regions with an accumulation of adipose tissue.

Neural substrates underlying rhythmic coupling of female reproductive and thermoregulatory circuits

Coordinated fluctuations in female reproductive physiology and thermoregulatory output have been reported for over a century. These changes occur rhythmically at the hourly (ultradian), daily (circadian), and multi-day (ovulatory) timescales, are critical for reproductive function, and have led to the use of temperature patterns as a proxy for female reproductive state. The mechanisms underlying coupling between reproductive and thermoregulatory systems are not fully established, hindering the expansion of inferences that body temperature can provide about female reproductive status. At present, numerous digital tools rely on temperature to infer the timing of ovulation and additional applications (e.g., monitoring ovulatory irregularities and progression of puberty, pregnancy, and menopause are developed based on the assumption that reproductive-thermoregulatory coupling occurs across timescales and life stages. However, without clear understanding of the mechanisms and degree of coupling among the neural substrates regulating temperature and the reproductive axis, whether such approaches will bear fruit in particular domains is uncertain. In this overview, we present evidence supporting broad coupling among the central circuits governing reproduction, thermoregulation, and broader systemic physiology, focusing on timing at ultradian frequencies. Future work characterizing the dynamics of reproductive-thermoregulatory coupling across the lifespan, and of conditions that may decouple these circuits (e.g., circadian disruption, metabolic disease) and compromise female reproductive health, will aid in the development of strategies for early detection of reproductive irregularities and monitoring the efficacy of fertility treatments.

Gender inequalities in heat-related mortality in the Czech Republic

It is acknowledged that climate change exacerbates social inequalities, and women have been reported as more vulnerable to heat than men in many studies in Europe, including the Czech Republic. This study aimed at investigating the associations between daily temperature and mortality in the Czech Republic in the light of a sex and gender perspective, taking into account other factors such as age and marital status. Daily mean temperature and individual mortality data recorded during the five warmest months of the year (from May to September) over the period 1995-2019 were used to fit a quasi-Poisson regression model, which included a distributed lag non-linear model (DLNM) to account for the delayed and non-linear effects of temperature on mortality. The heat-related mortality risks obtained in each population group were expressed in terms of risk at the 99th percentile of summer temperature relative to the minimum mortality temperature. Women were found generally more at risk to die because of heat than men, and the difference was larger among people over 85 years old. Risks among married people were lower than risks among single, divorced, and widowed people, while risks in divorced women were significantly higher than in divorced men. This is a novel finding which highlights the potential role of gender inequalities in heat-related mortality. Our study underlines the relevance of including a sex and gender dimension in the analysis of the impacts of heat on the population and advocates the development of gender-based adaptation policies to extreme heat.

Beating the heat: military training and operations in the era of global warming

Global climate change has resulted in an increase in the number and intensity of environmental heat waves, both in areas traditionally associated with hot temperatures and in areas where heat waves did not previously occur. For military communities around the world, these changes pose progressively increasing risks of heat-related illnesses and interference with training sessions. This is a significant and persistent "noncombat threat" to both training and operational activities of military personnel. In addition to these important health and safety concerns, there are broader implications in terms of the ability of worldwide security forces to effectively do their job (particularly in areas that historically already have high ambient temperatures). In the present review, we attempt to quantify the impact of climate change on various aspects of military training and performance. We also summarize ongoing research efforts designed to minimize and/or prevent heat injuries and illness. In terms of future approaches, we propose the need to "think outside the box" for a more effective training/schedule paradigm. One approach may be to investigate potential impacts of a reversal of sleep-wake cycles during basic training during the hot months of the year, to minimize the usual increase in heat-related injuries, and to enhance the capacity for physical training and combat performance. Regardless of which approaches are taken, a central feature of successful present and future interventions will be that they are rigorously tested using integrative physiological approaches.

Heat Adaptation for Females: A Systematic Review and Meta-Analysis of Physiological Adaptations and Exercise Performance in the Heat

BACKGROUND

Heat adaptation regimes are used to prepare athletes for exercise in hot conditions to limit a decrement in exercise performance. However, the heat adaptation literature mostly focuses on males, and consequently, current heat adaptation guidelines may not be optimal for females when accounting for the biological and phenotypical differences between sexes.

OBJECTIVES

We aimed to examine: (1) the effects of heat adaptation on physiological adaptations in females; (2) the impact of heat adaptation on performance test outcomes in the heat; and (3) the impact of various moderators, including duration (minutes and/or days), total heat dose (°C.min), exercise intensity (kcal.min-1), total energy expended (kcal), frequency of heat exposures and training status on the physiological adaptations in the heat.

METHODS

SPORTDiscus, MEDLINE Complete and Embase databases were searched to December 2022. Random-effects meta-analyses for resting and exercise core temperature, skin temperature, heart rate, sweat rate, plasma volume and performance tests in the heat were completed using Stata Statistical Software: Release 17. Sub-group meta-analyses were performed to explore the effect of duration, total heat dose, exercise intensity, total energy expended, frequency of heat exposure and training status on resting and exercise core temperature, skin temperature, heart rate and sweat rate. An explorative meta-regression was conducted to determine the effects of physiological adaptations on performance test outcomes in the heat following heat adaptation.

RESULTS

Thirty studies were included in the systematic review; 22 studies were meta-analysed. After heat adaptation, a reduction in resting core temperature (effect size [ES] =  - 0.45; 95% confidence interval [CI] - 0.69, - 0.22; p < 0.001), exercise core temperature (ES =  - 0.81; 95% CI - 1.01, - 0.60; p < 0.001), skin temperature (ES =  - 0.64; 95% CI - 0.79, - 0.48; p < 0.001), heart rate (ES =  - 0.60; 95% CI - 0.74, - 0.45; p < 0.001) and an increase in sweat rate (ES = 0.53; 95% CI 0.21, 0.85; p = 0.001) were identified in females. There was no change in plasma volume (ES = - 0.03; 95% CI - 0.31, 0.25; p = 0.835), whilst performance test outcomes were improved following heat adaptation (ES = 1.00; 95% CI 0.56, 1.45; p < 0.001). Across all moderators, physiological adaptations were more consistently observed following durations of 451-900 min and/or 8-14 days, exercise intensity ≥ 3.5 kcal.min-1, total energy expended ≥ 3038 kcal, consecutive (daily) frequency and total heat dose ≥ 23,000 °C.min. The magnitude of change in performance test outcomes in the heat was associated with a reduction in heart rate following heat adaptation (standardised mean difference =  - 10 beats.min-1; 95% CI - 19, - 1; p = 0.031).

CONCLUSIONS

Heat adaptation regimes induce physiological adaptations beneficial to thermoregulation and performance test outcomes in the heat in females. Sport coaches and applied sport practitioners can utilise the framework developed in this review to design and implement heat adaptation strategies for females.

Ovariectomy aggravates the pathophysiological response to exertional heat stroke in mice

Female mice have a greater capacity for exercising in the heat than male mice, reaching greater power output and longer times of heat exposure before succumbing to exertional heat stroke (EHS). Differences in body mass, size, or testosterone do not explain these distinct sex responses. Whether the ovaries could account for the superior exercise capacity in the heat in females remains unknown. Here, we determined the influence of ovariectomy (OVX) on exercise capacity in the heat, thermoregulation, intestinal damage, and heat shock response in a mouse EHS model. We performed bilateral OVX (n = 10) or sham (n = 8) surgeries in young adult (4 mo) female C57/BL6J mice. Upon recovery from surgeries, mice exercised on a forced wheel placed inside an environmental chamber set at 37.5 °C and 40% relative humidity until experiencing loss of consciousness (LOC). Terminal experiments were performed 3 h after LOC. OVX increased body mass by the time of EHS (sham = 3.8 ± 1.1, OVX = 8.3 ± 3.2 g, P < 0.05), resulted in shorter running distance (sham = 753 ± 189, OVX = 490 ± 87 m, P < 0.05), and shorter time to LOC (sham = 126.3 ± 21, OVX = 99.1 ± 19.8 min, P < 0.05). Histopathological assessment of the intestines revealed damage in the jejunum (sham = 0.2 ± 0.7, OVX = 2.1 ± 1.7 AU, P < 0.05) and ileum (sham = 0.3 ± 0.5, OVX = 1.8 ± 1.4 AU, P < 0.05). OVX increased mesenteric microvascular density (sham = 101 ± 25, OVX = 156 ± 66 10-2 mm/mm2, P < 0.05) and decreased concentration of circulatory heat shock protein 72 (HSP72) (sham = 26.7 ± 15.8, OVX = 10.3 ± 4.6 ng/mL, P < 0.05). No differences were observed in cytokines or chemokines between groups. Our findings indicate that OVX aggravates the pathophysiological response to EHS in mice.NEW & NOTEWORTHY Females outperform males in a mouse model of exertional heat stroke (EHS). Here, we show for the first time the impact of ovariectomy (OVX) on EHS pathophysiology. OVX resulted in a shorter exercise capacity in the heat, greater intestinal damage, and lower heat shock response following EHS.

Gender differences in motor and non-motor symptoms in individuals with mild-moderate Parkinson's disease

BACKGROUND

Parkinson's disease (PD) affects both men and women with documented gender differences across functional domains, with findings varying among reports. Knowledge regarding gender differences in PD for different geographic locations is important for further understanding of the disease and for developing personalized gender-specific PD assessment tools and therapies.

OBJECTIVE

This study aimed to examine gender differences in PD-related motor, motor-cognitive, cognitive, and psychosocial function in people with PD from the southern United States (US).

METHODS

199 (127 men and 72 women; M age: 69.08±8.94) individuals with mild-moderate idiopathic PD (Hoehn &Yahr (H&Y) Median = 2, stages I-III) from a large metro area in the southeastern US were included in this retrospective, cross-sectional study. Motor, motor-cognitive, cognitive, and psychosocial data were obtained using standardized and validated clinical tests. Univariate analyses were performed, adjusting for age and housing type.

RESULTS

After adjustment for age, housing, PD duration and fall rate, men exhibited statistically significantly greater motor (Movement Disorders Society (MDS)-Unified Parkinson Disease Rating Scale (UPDRS)-II) and non-motor (MDS-UPDRS-I) impact of PD, and more severe motor signs (MDS-UPDRS-III). Men exhibited worse PD-specific health-related quality of life related to mobility, activities of daily living, emotional well-being, cognitive impairment, communication, and more depressive symptoms. Men performed worse on a subtraction working memory task. Women had slower fast gait speed.

CONCLUSIONS

In the southeastern United States, men may experience worse PD-related quality of life and more depression than women. Many non-motor and motor variables that are not PD specific show no differences between genders in this cohort. These findings can contribute to the development of gender-sensitive assessment and rehabilitation policies and protocols for people with PD.

Gender differences in adaptation to heat in Spain (1983-2018)

In Spain the average temperature has increased by 1.7 °C since pre-industrial times. There has been an increase in heat waves both in terms of frequency and intensity, with a clear impact in terms of population health. The effect of heat waves on daily mortality presents important territorial differences. Gender also affects these impacts, as a determinant that conditions social inequalities in health. There is evidence that women may be more susceptible to extreme heat than men, although there are relatively few studies that analyze differences in the vulnerability and adaptation to heat by sex. This could be related to physiological causes. On the other hand, one of the indicators used to measure vulnerability to heat in a population and its adaptation is the minimum mortality temperature (MMT) and its temporal evolution. The aim of this study was to analyze the values of MMT in men and women and its temporal evolution during the 1983-2018 period in Spain's provinces. An ecological, longitudinal retrospective study was carried out of time series data, based on maximum daily temperature and daily mortality data corresponding to the study period. Using cubic and quadratic fits between daily mortality rates and the temperature, the minimum values of these functions were determined, which allowed for determining MMT values. Furthermore, we used an improved methodology that provided for the estimation of missing MMT values when polynomial fits were inexistent. This analysis was carried out for each year. Later, based on the annual values of MMT, a linear fit was carried out to determine the rate of evolution of MMT for men and for women at the province level. Average MMT for all of Spain's provinces was 29.4 °C in the case of men and 28.7 °C in the case of women. The MMT for men was greater than that of women in 86 percent of the total provinces analyzed, which indicates greater vulnerability among women. In terms of the rate of variation in MMT during the period analyzed, that of men was 0.39 °C/decade, compared to 0.53 °C/decade for women, indicating greater adaptation to heat among women, compared to men. The differences found between men and women were statistically significant. At the province level, the results show great heterogeneity. Studies carried out at the local level are needed to provide knowledge about those factors that can explain these differences at the province level, and to allow for incorporating a gender perspective in the implementation of measures for adaptation to high temperatures.

Androgen receptor suppresses β-adrenoceptor-mediated CREB activation and thermogenesis in brown adipose tissue of male mice

Thermoregulation is a process by which core body temperature is maintained in mammals. Males typically have a lower body temperature than females. However, the effects of androgens, which show higher levels in males, on adrenergic receptor-mediated thermogenesis remain unclear. Here, we demonstrate that androgen-androgen receptor (AR) signaling suppresses the β-adrenergic agonist-induced rise of core body temperature using castrated and AR knockout (ARKO) male mice. Furthermore, in vitro mechanistic studies show that activated AR inhibits cAMP response element (CRE)-mediated transcription by suppressing cAMP response element-binding protein (CREB) phosphorylation. The elevation of body temperature induced by the β-adrenergic agonist CL316243 was higher in ARKO and castrated mice than in the control mice. Similarly, CL316243 induced a greater increase in Uncoupling protein 1 (Ucp1) expression and CREB phosphorylation in the brown adipose tissue of ARKO mice than in that of controls. We determined that activation of AR by dihydrotestosterone suppressed β3-agonist- or forskolin-induced CRE-mediated transcription, which was prevented by AR antagonist. AR activation also suppressed CREB phosphorylation induced by forskolin. Moreover, we found AR nuclear localization, but not transcriptional activity, was necessary for the suppression of CRE-mediated transcription. Finally, modified mammalian two-hybrid and immunoprecipitation analyses suggest nuclear AR and CREB form a protein complex both in the presence and absence of dihydrotestosterone and forskolin. These results suggest androgen-AR signaling suppresses β-adrenoceptor-induced UCP1-mediated brown adipose tissue thermogenesis by suppressing CREB phosphorylation, presumably owing to a protein complex with AR and CREB. This mechanism explains sexual differences in body temperature, at least partially.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Thermoregulatory dynamics reveal sex-specific inflammatory responses to experimental autoimmune encephalomyelitis in mice: Implications for multiple sclerosis-induced fatigue in females

The course of multiple sclerosis (MS) is characterized by striking sex differences in symptoms such as fatigue and impaired thermal regulation, which are associated with aggravated systemic pro-inflammatory processes. The purpose of this study was to replicate these symptoms in experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice in the quest to advance the preclinical study of non-motor symptoms of MS. Male and female C57BL/6 mice exposed to a mild form of EAE were evaluated for the progression of clinical, behavioural, thermal, and inflammatory processes. We show higher susceptibility in females to EAE than males based on greater clinical score and cumulative disease index (CDI), fatigue-like and anxiety-like behaviours. Accordingly, infrared (IR) thermography indicated higher cutaneous temperatures in females from post-induction days 12-23. Females also responded to EAE with greater splenic and adrenal gland weights than males as well as sex-specific changes in pro- and anti-inflammatory cytokines. These findings provide the first evidence of a sex-specific thermal response to immune-mediated demyelination, thus proposing a non-invasive assessment approach of the psychophysiological dynamics in EAE mice. The results are discussed in relation to the thermoregulatory correlates of fatigue and how endogenously elevated body temperature without direct heat exposure may be linked to psychomotor inhibition in patients with MS.

Sex-specific stress and biobehavioral responses to human experimenters in rats

Important factors influencing the outcome of animal experiments in preclinical research are often overlooked. In the current study, the reaction of female and male rats toward the biological sex of a human experimenter was investigated in terms of anxiety-like behaviors and physiological stress responses, as measured by infrared (IR) thermography, circulating corticosterone (CORT) and oxytocin levels. Female rats displayed consistently exacerbated anxiety-related behaviors along with elevated body surface temperature during repeated exposure to male experimenters. Experimental stress further intensified thermal responses to a male experimenter, especially in female rats. The behavioral responses to a male experimenter in females were associated with higher circulating CORT and lower oxytocin levels. Similar responses were induced by a T-shirt worn by a human male. The findings suggest that psychophysiological responses of female rats to a male experimenter are influenced by both visual and olfactory cues. The results emphasize the need to not only consider sex differences in experimental animals, but also standardize and report the experimenter’s biological sex to avoid ambiguity in the generation and interpretation of results.

Do E2 and P4 contribute to the explained variance in core temperature response for trained women during exertional heat stress when metabolic rates are very high?

Purpose

Women remain underrepresented in the exercise thermoregulation literature despite their participation in leisure-time and occupational physical activity in heat-stressful environments continuing to increase. Here, we determined the relative contribution of the primary ovarian hormones (estrogen [E₂] and progesterone [P₄]) alongside other morphological (e.g., body mass), physiological (e.g., sweat rates), functional (e.g., aerobic fitness) and environmental (e.g., vapor pressure) factors in explaining the individual variation in core temperature responses for trained women working at very high metabolic rates, specifically peak core temperature (T_peak) and work output (mean power output).

Methods

Thirty-six trained women (32 ± 9 year, 53 ± 9 ml·kg⁻¹·min⁻¹), distinguished by intra-participant (early follicular and mid-luteal phases) or inter-participant (ovulatory vs. anovulatory vs. oral contraceptive pill user) differences in their endogenous E₂ and P₄ concentrations, completed a self-paced 30-min cycling work trial in warm–dry (2.2 ± 0.2 kPa, 34.1 ± 0.2 °C, 41.4 ± 3.4% RH) and/or warm–humid (3.4 ± 0.1 kPa, 30.2 ± 1.2 °C, 79.8 ± 3.7% RH) conditions that yielded 115 separate trials. Stepwise linear regression was used to explain the variance of the dependent variables.

Results

Models were able to account for 60% of the variance in T_peak (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 41% core temperature at the start of work trial, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 15% power output, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 4% [E₂]) and 44% of the variance in mean power output (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 35% peak aerobic power, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{R }$$\end{document}R¯²: 9% perceived exertion).

Conclusion

E₂ contributes a small amount toward the core temperature response in trained women, whereby starting core temperature and peak aerobic power explain the greatest variance in T_peak and work output, respectively.

Are there sex differences in risk for exertional heat stroke? A translational approach

NEW FINDINGS

What is the topic of this review? This review discusses the current status of the literature in sex differences in exertional heat stroke. What advances does this review highlight? We utilize a translational model to explore possible physical and physiological differences with respect risk and treatment of exertional heat stroke.

ABSTRACT

Exertional heat stroke (EHS) is a potentially fatal condition brought about by a combination of physical activity and heat stress and resulting in central nervous system dysfunction and organ damage. EHS impacts several hundred individuals each year ranging from military personnel, athletes, to occupational workers. Understanding the pathophysiology and risk factors can aid in reducing EHS across the globe. While we know there are differences between sexes in mechanisms of thermoregulation, there is currently not a clear understanding if/how those differences impact EHS risk. The purpose of this review is to assess the current status of the literature surrounding EHS from risk factors to treatment using both animal and human models. We use a translational approach, considering both animal and human research to elucidate the possible influence of female sex hormones on temperature regulation and performance in the heat and highlight the specific areas with limited research. While more work is necessary to comprehensively understand these differences, the current research presented provides a good framework for future investigations. This article is protected by copyright. All rights reserved.

Heat tolerance during uncompensable heat stress in men and women wearing firefighter personal protective equipment

Firefighters run a risk of heat strain during occupational tasks. The number of female firefighters has been increasing, but research relevant to this group is still scarce. We aimed to investigate whether there are any sex differences in heat tolerance or physiological responses during uncompensable heat stress while wearing firefighter personal protective equipment. Twelve female (28 ± 7 years, 66 ± 5 kg, 51.7 ± 4.7 mL kg^-1 min^-1) and 12 male (27 ± 7 years, 83 ± 8 kg, 58.8 ± 7.5 mL kg^-1 min^-1) participants performed walking (maximum of 60 min) at 6W·kg^-1, 40 °C, and 14% relative humidity. No differences were observed between groups in heat tolerance, rectal temperature, heart rate, percent body mass loss, thermal sensation, and rate of perceived exertion. Thus, when personnel are selected using gender-neutral physical employment standards, sex is not an independent factor influencing heat tolerance when wearing firefighter personal protective equipment during uncompensable heat stress.

Heat tolerance and the validity of occupational heat exposure limits in women during moderate-intensity work

To mitigate excessive rises in core temperature (>1°C) in non heat-acclimatized workers, the American Conference of Governmental Industrial Hygienists (ACGIH) provide heat stress limits (Action Limit Values; ALV), defined by the wet-bulb globe temperature (WBGT) and a worker's metabolic rate. However, since these limits are based on data from men, their suitability for women remains unclear. We therefore assessed core temperature and heart rate in men (n=19; body surface area-to-mass ratio: 250 (SD 17) cm2/kg) and women (n=15; body surface area-to-mass ratio: 268 (SD 24) cm2/kg) aged 18-45 years during 180-min walking at a moderate metabolic rate (200 W/m2) in WBGTs below (16 and 24°C) and above (28 and 32°C) ACGIH ALV. Sex did not significantly influence (i) rises in core temperature, irrespective of WBGT, (ii) the proportion of participants with rises in core temperature >1°C in environments below ACGIH limits, and (iii) work duration before rises in core temperature exceeded 1°C or volitional termination in environments above ACGIH limits. Although further studies are needed, these findings indicate that for the purpose of mitigating rises in core temperature exceeding recommended limits (>1°C), ACGIH guidelines have comparable effectiveness in non heat-acclimatized men and women when working at a moderate metabolic rate. Novelty points • Sex did not appreciably influence thermal strain nor the proportion of participants with core temperatures exceeding recommended limits. • Sex did not significantly influence tolerance to uncompensable heat stress • Despite originating from data obtained in only men, current occupational heat stress guidance offered comparable effectiveness in men and women.

Body Anthropometrics and Rectal Temperature Cooling Rates in Women With Hyperthermia

CONTEXT

Cold-water immersion (CWI) is the best treatment for exertional heat stroke (EHS), and rectal temperature (Trec) cooling rates may differ between sexes. Previous authors have suggested body surface area (BSA) to lean body mass (LBM) ratio is the largest factor affecting CWI Trec cooling rates in men with hyperthermia; this has never been confirmed in women with hyperthermia.

OBJECTIVE

To examine whether the BSA:LBM ratio and other anthropometrics affect Trec cooling rates in women with hyperthermia.

DESIGN

Cross-sectional study.

SETTING

Laboratory.

PATIENTS OR OTHER PARTICIPANTS

Sixteen women were placed in either a low BSA:LBM ratio (LOW; n = 8; age = 22 ± 1 years, height = 166.8 ± 6.0 cm, mass = 64.1 ± 4.5 kg, BSA:LBM ratio = 3.759 ± 0.214 m2/kg·102) or high BSA:LBM ratio group (HIGH; n = 8; age = 22 ± 2 years, height = 162.7 ± 8.9 cm, mass = 65.8 ± 12.7 kg, BSA:LBM ratio = 4.161 ± 0.232 m2/kg·102).

INTERVENTION(S)

On day 1, we measured physical characteristics using dual-energy x-ray absorptiometry, and participants completed a maximal oxygen consumption test. On day 2, participants walked at 4.8 km/h for 3 minutes and then ran at 80% of their predetermined maximal oxygen consumption for 2 minutes in the heat (temperature = ~40°C, relative humidity = 40%). This sequence was repeated until Trec reached 39.5°C. Then, they completed CWI (temperature = ~10°C) until Trec was 38°C.

MAIN OUTCOME MEASURE(S)

Rectal temperature and CWI cooling rates.

RESULTS

Groups had different BSA:LBM ratios (P = .001), body fat percentages (LOW: 25.7% ± 5.0%; HIGH: 33.7% ± 6.3%; P = .007), and LBM (LOW: 45.8 ± 3.0 kg; HIGH: 41.0 ± 5.1 kg; P = .02) but not different BSA (LOW: 1.72 ± 0.08 m2; HIGH: 1.70 ± 0.16 m2; P = .40) or BMI (LOW: 23.1 ± 2.1; HIGH: 24.9 ± 4.7; P = .17). Despite differences in several physical characteristics, Trec cooling rates were excellent but comparable (LOW: 0.26°C/min ± 0.09°C/min; HIGH: 0.27°C/min ± 0.07°C/min; P = .39). The BSA:LBM ratio (r = 0.14, P = .59), body fat percentage (r = 0.29, P = .28), LBM (r = -0.10, P = .70), BSA (r = -0.01, P = .97), and BMI (r = 0.37, P = .16) were not correlated with Trec cooling rates.

CONCLUSIONS

Body anthropometrics did not affect CWI Trec cooling rates in women with hyperthermia. Clinicians need not worry about anthropometric characteristics slowing the treatment of severe hyperthermia in women using CWI.

Vagally Derived Heart Rate Variability and Training Perturbations With Menses in Female Collegiate Rowers

INTRODUCTION

The parasympathetically derived marker of heart rate variability, root mean square of successive R-R differences (RMSSD), and the daily fluctuations as measured by the coefficient of variation (RMSSDCV) may be useful for tracking training adaptations in athletic populations. These vagally derived markers of heart rate variability may be especially pertinent when simultaneously considering a female athlete's menstrual cycle.

PURPOSE

The purpose of this study was to observe the perturbations in RMSSDCV, while considering RMSSD, across a season in the presence and absence of menses with training load in female collegiate rowers.

METHODS

Thirty-six (20 [1] y, 25.6 [3.4] kg·m-2) National Collegiate Athletic Association Division I female rowers were monitored for 18 consecutive weeks across a full season. Seated, ultrashortened RMSSD measurements were obtained by the rowers on at least 3 mornings per week using a smartphone photoplethysmography device. Following the RMSSD measurement, athletes indicated the presence or absence of menstruation within the application. Individual meters rowed that week and sessions rate of perceived exertion were obtained to quantify training load.

RESULTS

Longitudinal mixed-effects modeling demonstrated a significant effect of menses and time, while also considering RMSSD, such that those who were on their period had a significantly greater RMSSDCV than those who were not (11.2% vs 7.5%, respectively; P < .001). These changes were independent of meters rowed, sessions rate of perceived exertion, body mass index, birth-control use, and years of rowing experience, which were all nonsignificant predictors of RMSSDCgV (P > .05).

CONCLUSION

The presence of menses appears to significantly impact RMSSDCV when also considering RMSSD, which may allow coaches to consider individualized training plans accordingly.

Impact of the Hormonal Status in Women on Intraoperative Hypothermia during Laparoscopic Gynecologic Surgery when Considering the Fresh Gas Flow Rate: A Retrospective Study

Previous studies reported the impact of intrinsic and extrinsic factors on intraoperative hypothermia. However, no clinical study to date has considered the effects of both the phase of the menstrual cycle (an intrinsic factor) and the fresh gas flow rate (FGF) during anesthesia (an extrinsic factor) on the core body temperature and intraoperative hypothermia. This study is aimed at investigatig the effect of the menstrual cycle phase on intraoperative hypothermia when considering the FGF in patients who underwent laparoscopic gynecologic surgery. This study included 667 women aged 19-65 years with menstruation cycles and menopause. The patients were divided into the follicular, luteal, and menopause groups. The primary outcome was the correlations of hormonal status with intraoperative hypothermia. Secondary outcomes included the incidence of intraoperative hypothermia, time to onset of hypothermia, incidence of shivering after anesthesia, and frequency of antishivering drug use in the three groups and risk factors for hypothermia. Overall, the hypothermia incidence was the lowest and the time to onset of hypothermia was the longest in the luteal phase group. At a high FGF, the incidence of hypothermia in the luteal phase group was lower than that in the other two groups (P < 0.05). At a low FGF, the time to onset of hypothermia in the luteal phase group was longer than that in the other two groups (P < 0.05). The female hormonal status had weak positive correlations with hypothermia at low and high FGF rates. A high FGF in univariate and multivariate analyses, follicular phase and menopause in multivariate analysis, and estradiol and progesterone levels in univariate analysis were risk factors for hypothermia. When considering the FGF, the luteal phase is associated with better outcomes concerning intraoperative hypothermia.

Investigation of the Effects of Cardiovascular Therapeutic Ultrasound Applied in Female and Male Rats' Hearts of Different Ages

This study investigates the role of age and sex on the cardiovascular effects of 3.5-MHz pulsed ultrasound (US) in a rat model. Ultrasonic bursts of 2.0-MPa peak rarefactional pressure amplitude (equivalent to an in vitro spatial-peak temporal-peak intensity of ~270 W/cm2 and a mechanical index of 1.1) were delivered in five consecutive 10-s intervals, one interval for each pulse repetition frequency (PRF) (6, 5, 4, 5, and 6 Hz; always the same order) for a total exposure duration of 50 consecutive seconds. Sixty F344 rats were split into 12 groups in a 3×2×2 factorial design (three ages, male versus female, and US application versus control). This study is the first study on US-induced cardiac effects that contains data across three age groups of rats (premenopause, fertile, and postmenopause) to mimic the fertile and nonfertile human window. US was applied transthoracically, while heart rate, stroke volume, ejection fraction, temperature, and other physiologic parameters were recorded at baseline and after exposure. Significant decreases in cardiac output compared to respective control groups were observed in multiple experimental groups, spanning both females and males. A negative chronotropic effect was observed in young male (~7%) and female (~16%) rats, in five-month-old male (~9%) and female (~15%) rats, and in old rats where the effect was not statistically significant. Younger groups and, to a lesser extent, lower weight groups generally had more significant effects. The pathophysiology of US-induced cardiovascular effects appears to be multifactorial and not strictly related to hormones, menopause, weight, sex, or age, individually.

The effects of a novel personal comfort system on thermal comfort, physiology and perceived indoor environmental quality, and its health implications - Stimulating human thermoregulation without compromising thermal comfort

The classical textbook interpretation of thermal comfort is that it occurs when the thermoregulatory effort is minimized. However, stimulating human thermoregulatory systems may benefit health and increase body thermal resilience. To address this gap, we tested a novel personal comfort system (PCS) that targets only the extremities and the head, leaving the rest of the body exposed to a moderately drifting temperature (17-25°C). A randomized, cross-over study was conducted under controlled laboratory conditions, mimicking an office setting. Eighteen participants completed two scenarios, one with a PCS and another one without a PCS in 17-25°C ambient conditions. The results indicate that the PCS improved thermal comfort in 17-23°C and retained active thermoregulatory control. The torso skin temperature, underarm-finger temperature gradients, energy expenditure, substrate oxidations and physical activity were not affected by the PCS in most cases. Only slight changes in cardiovascular responses were observed between the two scenarios. Moreover, the PCS boosted pleasure and arousal. At 25°C, the PCS did not improve thermal comfort, but significantly improved air quality perceptions and mitigated eye strain. These findings suggest that human physiological thermoregulation can be stimulated without compromising thermal comfort by using a PCS that only targets the extremities in cold conditions.

Sex-based differences in body core temperature response across repeat work bouts in the heat

OBJECTIVE

To investigate the effects of repeated work bouts in the heat on peak body core temperature and to explore sex-based differences in body core temperature responses.

METHODS

Fourteen males and fifteen females performed four work bouts (two heavy and two moderate, alternating) in 32.5 °C Wet Bulb Globe Temperature (WBGT), each separated by 30-min seated rest in 28.0 °C WBGT. Participants wore a military combat uniform with body armour and helmet (10 kg load) during the work bouts, removing the vest and helmet during recovery periods.

RESULTS

Body core temperature elevation over time was faster in the first compared with subsequent work bouts of each intensity. Body core temperature elevation was similar between males and females during the first heavy work bout, then remained significantly lower in females for the reminder of the trial.

CONCLUSIONS

Contrary to the assumed progressive elevation in strain, but in agreement with recent literature, a gradual reduction in heat storage in subsequent exercise bouts prevented a cumulative increase in heat strain in the conditions tested.

A novel PCOS rat model and an evaluation of its reproductive, metabolic, and behavioral phenotypes

Background

Although animal models of PCOS have been used in many studies, none of them can reproduce both the reproductive and metabolic phenotypes of PCOS. In addition, behavioral parameters have not been evaluated in PCOS animal models.

Purpose

We tried to produce an improved rat model of PCOS, and the reproductive, metabolic, and behavioral phenotypes of the model rats were evaluated.

Methods

Female rats were implanted with silicon tubes containing oil-dissolved dihydrotestosterone (Oil-DHT) as a new PCOS model. Their phenotypes were compared with those of conventional PCOS model rats (DHT), into which tubes containing crystalline DHT were implanted, and non-DHT-treated rats (control).

Results

Both the Oil-DHT and DHT rats showed greater body weight gain, food intake, and fat depot weight than the control rats. Furthermore, these groups showed fewer estrous stages and increased numbers of cystic follicles. The DHT rats exhibited lower ovarian and uterine weights than the control rats, whereas no such changes were observed in the Oil-DHT rats. The Oil-DHT and DHT rats showed less locomotor activity in the light phase than the control rats.

Conclusions

Our proposed PCOS model reproduced both the reproductive and metabolic phenotypes of PCOS and may have potential for PCOS research.

Physiological costs of undocumented human migration across the southern United States border

[Figure: see text].

Effects of Female Reproductive Hormone Levels on Inadvertent Intraoperative Hypothermia during Laparoscopic Gynecologic Surgery: A Retrospective Study

Background and Objectives: Female reproductive hormones may affect core body temperature. This study aimed to investigate the effects of female reproductive hormones on inadvertent intraoperative hypothermia in patients who underwent laparoscopic gynecologic surgery under general anesthesia. Materials and Methods: This retrospective study included 660 menstruating and menopausal female patients aged 19–65 years. The patients were divided into two groups according to the occurrence of inadvertent intraoperative hypothermia: non-hypothermia group (N = 472) and hypothermia group (N = 188). After propensity score matching, 312 patients (N = 156 in each group) were analyzed to investigate the association between intraoperative hypothermia and female reproductive hormones. As potential predictors of inadvertent hypothermia, the levels of female reproductive hormones were analyzed using binary logistic regression. Results: The association of estradiol (r = −0.218, p = 0.000) and progesterone (r = −0.235, p = 0.000) levels with inadvertent intraoperative hypothermia was significant but weakly negative before matching; however, it was significant and moderately negative after matching (r = −0.326, p = 0.000 and r = −0.485, p = 0.000, respectively). In a binary logistic analysis, the odds ratio for estradiol was 0.995 (p = 0.014, 0.993 < 95% confidence interval [CI] < 0.998) before matching and 0.993 (p = 0.000, 0.862 < 95% CI < 0.930) after matching, and that for progesterone was 0.895 (p = 0.000, 0.862 < 95% CI < 0.930) before matching and 0.833 (p = 0.014, 0.990 < 95% CI < 0.996) after matching. Conclusions: Estradiol and progesterone levels were associated with inadvertent intraoperative hypothermia. However, the odds ratio for female reproductive hormone levels was close to 1. Therefore, female reproductive hormones may not be a risk factor for hypothermia during gynecologic surgery under general anesthesia. However, a small sample size in this study limits the generalizability of the results.

Estrogen to Progesterone Ratio and Fluid Regulatory Responses to Varying Degrees and Methods of Dehydration

The purpose of this study was to investigate the relationship between volume regulatory biomarkers and the estrogen to progesterone ratio (E:P) prior to and following varying methods and degrees of dehydration. Ten women (20 ± 1 year, 56.98 ± 7.25 kg, 164 ± 6 cm, 39.59 ± 2.96 mL•kg•min⁻¹) completed four intermittent exercise trials (1.5 h, 33.8 ± 1.3°C, 49.5 ± 4.3% relative humidity). Testing took place in two hydration conditions, dehydrated via 24-h fluid restriction (Dehy, USG > 1.020) and euhydrated (Euhy, USG ≤ 1.020), and in two phases of the menstrual cycle, the late follicular phase (days 10–13) and midluteal phase (days 18–22). Change in body mass (%BMΔ), serum copeptin concentration, and plasma osmolality (P_osm) were assessed before and after both dehydration stimuli (24-h fluid restriction and exercise heat stress). Serum estrogen and progesterone were analyzed pre-exercise only. Estrogen concentration did not differ between phases or hydration conditions. Progesterone was significantly elevated in luteal compared to follicular in both hydration conditions (Dehy—follicular: 1.156 ± 0.31, luteal: 5.190 ± 1.56 ng•mL⁻¹, P < 0.05; Euhy—follicular: 0.915 ± 0.18, luteal: 4.498 ± 1.38 ng·mL⁻¹, P < 0.05). As expected, E:P was significantly greater in the follicular phase compared to luteal in both hydration conditions (Dehy—F:138.94 ± 89.59, L: 64.22 ± 84.55, P < 0.01; Euhy—F:158.13 ± 70.15, L: 50.98 ± 39.69, P < 0.01, [all •10³]). Copeptin concentration was increased following 24-h fluid restriction and exercise heat stress (mean change: 18 ± 9.4, P < 0.01). We observed a possible relationship of lower E:P and higher copeptin concentration following 24-h fluid restriction (r = −0.35, P = 0.054). While these results did not reach the level of statistical significance, these data suggest that the differing E:P ratio may alter fluid volume regulation during low levels of dehydration but have no apparent impact after dehydrating exercise in the heat.

Measurement error of self-paced exercise performance in athletic women is not affected by ovulatory status or ambient environment

Measurement error(s) of exercise tests for women are severely lacking in the literature. The purpose of this investigation was to 1) determine whether ovulatory status or ambient environment were moderating variables when completing a 30-min self-paced work trial and 2) provide test-retest norms specific to athletic women. A retrospective analysis of three heat stress studies was completed using 33 female participants (31 ± 9 yr, 54 ± 10 mL·min^-1·kg^-1) that yielded 130 separate trials. Participants were classified as ovulatory (n = 19), anovulatory (n = 4), and oral contraceptive pill users (n = 10). Participants completed trials ∼2 wk apart in their (quasi-) early follicular and midluteal phases in two of moderate (1.3 ± 0.1 kPa, 20.5 ± 0.5°C, 18 trials), warm-dry (2.2 ± 0.2 kPa, 34.1 ± 0.2°C, 46 trials), or warm-humid (3.4 ± 0.1 kPa, 30.2 ± 1.1°C, 66 trials) environments. We quantified reliability using limits of agreement, intraclass correlation coefficient (ICC), standard error of measurement (SEM), and coefficient of variation (CV). Test-retest reliability was high, clinically valid (ICC = 0.90, P < 0.01), and acceptable with a mean CV of 4.7%, SEM of 3.8 kJ (2.1 W), and reliable bias of -2.1 kJ (-1.2 W). The various ovulatory status and contrasting ambient conditions had no appreciable effect on reliability. These results indicate that athletic women can perform 30-min self-paced work trials ∼2 wk apart with an acceptable and low variability irrespective of their hormonal status or heat-stressful environments.NEW & NOTEWORTHY This study highlights that aerobically trained women perform 30-min self-paced work trials ∼2 wk apart with acceptably low variability and their hormonal/ovulatory status and the introduction of greater ambient heat and humidity do not moderate this measurement error.

Strenuous exercise in warm environment is associated with improved microvascular function in sickle cell trait

PURPOSE

Sickle cell trait is characterized by the presence of both normal and abnormal haemoglobin in red blood cells. The rate of exertional collapse is increased in athletes and military recruits who carry the trait, particularly in stressful environmental conditions. The aim of the present study was to investigate microvascular function and its determinants in response to intense exercise at control and warm environmental temperatures in carriers (AS) and non-carriers (AA) of sickle cell trait.

METHODS

Nine AS and 11 AA, all healthy physically active young men, randomly participated in four experimental sessions (rest at 21 °C and 31 °C and cycling at 21 °C and 31 °C). All participants performed three exercises bouts as follows: 18-min submaximal exercise; an incremental test to exhaustion; and three 30-s sprints spaced with 20-s resting intervals.

RESULTS

Skin Blood Flow (SkBF) was similar at rest between AA and AS. SkBF for all participants was higher at 31 °C than 21 °C. It was significantly higher in the AS group compared to the AA group immediately after exercise, regardless of the environmental conditions. No significant differences in hemorheological parameters, muscle damage or cardiac injury biomarkers were observed between the two groups. Our data also suggest higher oxidative stress for the AS group, with high superoxide dismutase (P = 0.044 main group effect).

CONCLUSION

A specific profile is identified in the AS population, with increased microvascular reactivity after maximal exercise in stressful environment and slight pro-/antioxidant imbalance.

Subjective sleep quality and characteristics across the menstrual cycle in women with and without Generalized Anxiety Disorder

OBJECTIVE

Past studies have found that various psychiatric symptoms fluctuate over the menstrual cycle. Sleep disturbance is a transdiagnostic feature of psychiatric conditions and is associated with several symptoms that exhibit menstrual fluctuations. Although some evidence indicates that subjective sleep quality changes over the menstrual cycle in healthy women, no studies have investigated whether sleep fluctuates over the menstrual cycle in psychiatric populations, other than premenstrual dysphoric disorder.

METHODS

The present study used a mixed between- within-groups design to compare self-reported sleep characteristics (sleep onset latency, number and duration of night-time awakenings, and total sleep time), sleep quality, insomnia symptoms, and daytime sleepiness in women with (n = 31) and without (n = 32) generalized anxiety disorder (GAD) at two time points within a single menstrual cycle - the early-follicular (low ovarian hormones) and mid-luteal (high ovarian hormones) phases.

RESULTS

Women with GAD reported lower sleep quality, more insomnia symptoms, and more daytime sleepiness (η_p² = 0.13-0.14), but comparable sleep characteristics, compared to women without GAD. In both groups, sleep variables remained stable over the menstrual phases examined. Within-person changes in estradiol and progesterone between the two menstrual phases were mostly not associated with within-person changes in sleep variables, except that larger increases in estradiol were associated with a reduction in the number of night-time awakenings from the early-follicular to mid-luteal phases (β = -0.26).

CONCLUSION

These findings indicate that subjective sleep disturbance, unlike other psychiatric symptoms, may not be modulated by the menstrual cycle and ovarian hormones during the phases examined in this study.

The development and initial validation of the Health and Reproductive Survey (HeRS)

Background:

Due to the diversity in profiles associated with the female reproductive cycle and their potential physiological and psychological effects, monitoring the reproductive status of exercising females is important from a practical and research perspective. Moreover, as physical activity can influence menstrual function, the effects of physical activity energy expenditure on reproductive function should also be considered.

Aim:

The aim of this study was to develop and establish initial face and content validity of the Health and Reproductive Survey (HeRS) for physically active females, which is a retrospective assessment of menstrual function from menarche (first menstruation) to menopause (cessation of menstruation).

Methods:

Face validity was evaluated qualitatively, and the initial content validity was established through a principal component analysis. The face validity process was completed by 26 females aged 19–67 years and the content validity was established through a survey sent to a convenience sample of 392 females, of which 230 females (57.9% and aged 18–49 years) completed the survey.

Results:

The revisions made following the face validation improved the understanding, flow, and coherence of the survey. The principal component analysis indicated that, at a minimum, the survey measures these constructs: menstrual cessation and associated moderators, athletic participation and performance levels (as associated with menstruation change and the menstrual cycle), age and menstrual cessation, hormonal contraception (“birth control”), and menarche and associated moderators.

Conclusion:

The Health and Reproductive Survey (HeRS) is a partially validated tool that can be used by researchers to characterize the menstrual status of physically active females relative to their physical activity status.

Sex difference in initial thermoregulatory response to dehydrated exercise in the heat

Although it is well established that dehydration has a negative impact on thermoregulation during exercise in the heat, it is unclear whether this effect of dehydration is different between men and women, or across the phases of the menstrual cycle (MC). Twelve men and seven women (men: 20 ± 2 years, 70.13 ± 10.5 kg, 173.4 ± 6.0 cm, 54.2 ± 8.6 ml kg-1  min-1 ; women: 20 ± 2 years, 57.21 ± 7.58 kg, 161 ± 5 cm, 40.39 ± 3.26 ml kg-1  min-1 ) completed trials either euhydrated (urine specific gravity, USG ≤ 1.020, Euhy) or dehydrated (USG > 1.020, Dehy). Trial order was randomized and counterbalanced; men completed two trials (MEuhy and MDehy) and women completed four over two MC phases (late follicular: days 10-13, FDehy, FEuhy; midluteal: days 18-22, LDehy, LEuhy). Each trial consisted of 1.5 h, split into two 30 min blocks of exercise (B1 and B2, 15 min at 11 W/kg & 15 min at 7 W/kg) separated by 15 min rest in between and after. Rectal temperature (Tre ) was measured continuously and estimated sweat loss was calculated from the body mass measured before and after each block of exercise. When dehydrated, the rate of rise in Tre was greater in women in the first block of exercise compared to men, independently of the MC phase (MDehy: 0.03 ± 0.03°C/min, FDehy: 0.06 ± 0.02, LDehy: 0.06 ± 0.02, p = 0.03). Estimated sweat loss was lower in all groups in B1 compared to B2 when dehydrated (p < 0.05), with no difference between sexes for either hydration condition. These data suggest that women may be more sensitive to the negative thermoregulatory effects of dehydration during the early stages of exercise in the heat.

Roundtable on Preseason Heat Safety in Secondary School Athletics: Heat Acclimatization

OBJECTIVE

To provide best-practice recommendations for developing and implementing heat-acclimatization strategies in secondary school athletics.

DATA SOURCES

An extensive literature review on topics related to heat acclimatization and heat acclimation was conducted by a group of content experts. Using the Delphi method, action-oriented recommendations were developed.

CONCLUSIONS

A period of heat acclimatization consisting of ≥14 consecutive days should be implemented at the start of fall preseason training or practices for all secondary school athletes to mitigate the risk of exertional heat illness. The heat-acclimatization guidelines should outline specific actions for secondary school athletics personnel to use, including the duration of training, the number of training sessions permitted per day, and adequate rest periods in a cool environment. Further, these guidelines should include sport-specific and athlete-specific recommendations, such as phasing in protective equipment and reintroducing heat acclimatization after periods of inactivity. Heat-acclimatization guidelines should be clearly detailed in the secondary school's policy and procedures manual and disseminated to all stakeholders. Heat-acclimatization guidelines, when used in conjunction with current best practices surrounding the prevention, management, and care of secondary school student-athletes with exertional heat stroke, will optimize their health and safety.

Female (Under) Representation in Exercise Thermoregulation Research

BACKGROUND

Despite an increasing rate of women participating in professional sports, emergency services, and military settings where they are exposed to exertional heat stress, our understanding of female thermoregulation and the detrimental effects of heat on women's performance, especially regarding the menstrual cycle, is limited. This review aimed to quantify the representation of women in exercise thermoregulation research between 2010 and 2019 and the frequency that these articles reported details pertaining to female participants' menstrual cycle to determine the volume of novel research that is directly relevant to this growing population.

METHODS

Original exercise thermoregulatory studies published in three major sports medicine databases (PubMed, MEDLINE, and SPORTDiscus) between 2010 and 2019 were surveyed. Articles were screened to determine the number of female and male participants in the study and whether studies involving women reported menstrual orientation or phase. Research involving healthy adult participants and an exercise protocol with a thermoregulatory outcome measure were included in the review.

RESULTS

A total of 1407 articles were included in the review, involving 28,030 participants. The annual representation of women ranged from a mean of 11.6% [95% credible interval (CI); 9.2, 14.3] to 17.8% [95% CI; 15.2, 20.6] across the 10 years, indicating studies predominantly included men. Nonetheless, there was a small statistical increase in the overall proportion of women, with a mean overall proportion change of 0.7% [95% CI; 0.2, 1.2] per year. The increase appeared to be driven by a reduction in the number of studies including only men, rather than studies including more women alongside men, or increased women-only studies. Less than one third of articles involving women reported the menstrual orientation of participants and less than one quarter reported both menstrual orientation and phase. This study shows that women were proportionally underrepresented in exercise thermoregulation research during the past decade and the majority of studies did not report menstrual cycle details of female participants. Researchers should consider including women in future work where their inclusion could contribute meaningful data that enhance the evidence-based and ultimately improves our comprehension of women's thermal physiology.