Global reductions in manual agricultural work capacity due to climate change.

Manual outdoor work is essential in many agricultural systems. Climate change will make such work more stressful in many regions due to heat exposure. The physical work capacity metric (PWC) is a physiologically based approach that estimates an individual's work capacity relative to an environment without any heat stress. We computed PWC under recent past and potential future climate conditions. Daily values were computed from five earth system models for three emission scenarios (SSP1-2.6, SSP3-7.0, and SSP5-8.5) and three time periods: 1991-2010 (recent past), 2041-2060 (mid-century) and 2081-2100 (end-century). Average daily PWC values were aggregated for the entire year, the growing season, and the warmest 90-day period of the year. Under recent past climate conditions, the growing season PWC was below 0.86 (86% of full work capacity) on half the current global cropland. With end-century/SSP5-8.5 thermal conditions this value was reduced to 0.7, with most affected crop-growing regions in Southeast and South Asia, West and Central Africa, and northern South America. Average growing season PWC could falls below 0.4 in some important food production regions such as the Indo-Gangetic plains in Pakistan and India. End-century PWC reductions were substantially greater than mid-century reductions. This paper assesses two potential adaptions-reducing direct solar radiation impacts with shade or working at night and reducing the need for hard physical labor with increased mechanization. Removing the effect of direct solar radiation impacts improved PWC values by 0.05 to 0.10 in the hottest periods and regions. Adding mechanization to increase horsepower (HP) per hectare to levels similar to those in some higher income countries would require a 22% increase in global HP availability with Sub-Saharan Africa needing the most. There may be scope for shifting to less labor-intensive crops or those with labor peaks in cooler periods or shift work to early morning.

The 2023 report of the MJA-Lancet Countdown on health and climate change: sustainability needed in Australia's health care sector.

The MJA-Lancet Countdown on health and climate change in Australia was established in 2017 and produced its first national assessment in 2018 and annual updates in 2019, 2020, 2021 and 2022. It examines five broad domains: health hazards, exposures and impacts; adaptation, planning and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement. In this, the sixth report of the MJA-Lancet Countdown, we track progress on an extensive suite of indicators across these five domains, accessing and presenting the latest data and further refining and developing our analyses. Our results highlight the health and economic costs of inaction on health and climate change. A series of major flood events across the four eastern states of Australia in 2022 was the main contributor to insured losses from climate-related catastrophes of $7.168 billion - the highest amount on record. The floods also directly caused 23 deaths and resulted in the displacement of tens of thousands of people. High red meat and processed meat consumption and insufficient consumption of fruit and vegetables accounted for about half of the 87 166 diet-related deaths in Australia in 2021. Correction of this imbalance would both save lives and reduce the heavy carbon footprint associated with meat production. We find signs of progress on health and climate change. Importantly, the Australian Government released Australia's first National Health and Climate Strategy, and the Government of Western Australia is preparing a Health Sector Adaptation Plan. We also find increasing action on, and engagement with, health and climate change at a community level, with the number of electric vehicle sales almost doubling in 2022 compared with 2021, and with a 65% increase in coverage of health and climate change in the media in 2022 compared with 2021. Overall, the urgency of substantial enhancements in Australia's mitigation and adaptation responses to the enormous health and climate change challenge cannot be overstated. Australia's energy system, and its health care sector, currently emit an unreasonable and unjust proportion of greenhouse gases into the atmosphere. As the Lancet Countdown enters its second and most critical phase in the leadup to 2030, the depth and breadth of our assessment of health and climate change will be augmented to increasingly examine Australia in its regional context, and to better measure and track key issues in Australia such as mental health and Aboriginal and Torres Strait Islander health and wellbeing.

Work-rest regimens for work in hot environments: A scoping review.

BACKGROUND: To limit exposures to occupational heat stress, leading occupational health and safety organizations recommend work-rest regimens to prevent core temperature from exceeding 38°C or increasing by ≥1°C. This scoping review aims to map existing knowledge of the effects of work-rest regimens in hot environments and to propose recommendations for future research based on identified gaps. METHODS: We performed a search of 10 databases to retrieve studies focused on work-rest regimens under hot conditions. RESULTS: Forty-nine articles were included, of which 35 were experimental studies. Most studies were conducted in laboratory settings, in North America (71%), on healthy young adults, with 94% of the 642 participants being males. Most studies (66%) employed a protocol duration ≤240 min (222 ± 162 min, range: 37-660) and the time-weighted average wet-bulb globe temperature was 27 ± 4°C (range: 18-34). The work-rest regimens implemented were those proposed by the American Conference of Governmental and Industrial Hygiene (20%), National Institute of Occupational Safety and Health (11%), or the Australian Army (3%). The remaining studies (66%) did not mention how the work-rest regimens were derived. Most studies (89%) focused on physical tasks only. Most studies (94%) reported core temperature, whereas only 22% reported physical and/or mental performance outcomes, respectively. Of the 35 experimental studies included, 77% indicated that core temperature exceeded 38°C. CONCLUSIONS: Although work-rest regimens are widely used, few studies have investigated their physiological effectiveness. These studies were mainly short in duration, involved mostly healthy young males, and rarely considered the effect of work-rest regimens beyond heat strain during physical exertion.

The effect of synthetic grass sports surfaces on the thermal environment: A systematic review.

There are concerns regarding high surface temperatures on synthetic grass sports surfaces influencing the surrounding thermal environment, potentially increasing heat stress and impacting athlete safety. As such, studies have investigated changes to the thermal environment surrounding synthetic grass surfaces in comparison to both natural grass, and synthetic surfaces with different features, but this body of research has not been systematically reviewed. Therefore, this systematic review aimed to (i) determine if there are differences in the thermal environment surrounding synthetic grass surfaces compared with natural grass surfaces, and (ii) determine if there are differences in the thermal environment between different types of synthetic grass surfaces. A systematic review adhering to the PRISMA guidelines was performed. The eligibility criteria required investigations to report at least one of the following environmental parameters on or directly above both a synthetic surface and a comparator group of either natural grass or an alternative synthetic grass surface used in sport: Air temperature, mean radiant temperature, humidity, wind velocity, unified heat stress indices (i.e. wet-bulb-globe temperature and heat index) and/or surface temperature. Twenty-three studies were identified. The only parameters that were consistently higher on synthetic grass compared to natural grass were the air temperature (range: 0.5-1.2 °C) and surface temperature (range: 9.4-33.7 °C), while the mean radiant temperature, humidity, wind velocity and wet-bulb-globe temperature remained similar or required more data to determine if any differences exist. Synthetic grass surfaces consisting of styrene butadiene rubber infill or a shock pad had increased surface temperatures, whereas surfaces with thermoplastic elastomer infill, Cool climate turf fibres or HydroChill had lower surface temperatures. This systematic review has demonstrated that air and surface temperatures can be increased on synthetic sports surfaces, compared to natural grass surfaces. However, it is uncertain whether the differences are enough to increase an individual's heat stress risk and cause concern for athlete safety. While modifications to the turf infill or fibres can reduce synthetic surface temperatures, the effect of these features on the thermal environment as a whole is unclear. This review was prospectively registered with the Open Science Framework (Open Science Framework registration   https://doi.org/10.17605/OSF.IO/BTKGE ).

IOC consensus statement on recommendations and regulations for sport events in the heat.

This document presents the recommendations developed by the IOC Medical and Scientific Commission and several international federations (IF) on the protection of athletes competing in the heat. It is based on a working group, meetings, field experience and a Delphi process. The first section presents recommendations for event organisers to monitor environmental conditions before and during an event; to provide sufficient ice, shading and cooling; and to work with the IF to remove regulatory and logistical limitations. The second section summarises recommendations that are directly associated with athletes' behaviours, which include the role and methods for heat acclimation; the management of hydration; and adaptation to the warm-up and clothing. The third section explains the specific medical management of exertional heat stroke (EHS) from the field of play triage to the prehospital management in a dedicated heat deck, complementing the usual medical services. The fourth section provides an example for developing an environmental heat risk analysis for sport competitions across all IFs. In summary, while EHS is one of the leading life-threatening conditions for athletes, it is preventable and treatable with the proper risk mitigation and medical response. The protection of athletes competing in the heat involves the close cooperation of the local organising committee, the national and international federations, the athletes and their entourages and the medical team.

Optimal low-cost cooling strategies for infant strollers during hot weather.

The current study aimed to identity the optimal low-cost stroller cooling strategies for use in hot and moderately humid summer weather. A commercially available stroller was instrumented to assess the key parameters of the thermal environment. The cooling efficacy of eight different stroller configurations was examined in a counterbalanced order across 16 hot summer days (air temperature (Ta) = 33.3 ± 4.1 °C; relative humidity = 36.7 ± 15%; black globe temperature = 43.9 ± 4.6 °C). Compared with a standard-practice stroller configuration, combining a moist muslin draping with a battery-operated clip-on fan provided optimal in-stroller cooling, reducing the end-trial air temperature by 4.7 °C and the wet bulb globe temperature (WBGT) by 1.4 °C. In contrast, in-stroller temperatures were substantially increased by draping a dry muslin (Ta = +2.6 °C; WBGT = +0.9 °C) or flannelette (Ta = +3.7 °C; WBGT = +1.4 °C) cloth over the stroller carriage. These findings provide empirical evidence which may inform guidance aimed at protecting infants during hot weather.Practitioner summary: This study examined the efficacy of traditional and novel stroller cooling strategies for use in hot and moderately humid weather. Covering the carriage with a dry muslin cloth substantially increased stroller temperatures and should be avoided. Evaporative cooling methods reduced in-stroller temperatures. A moist muslin cloth draping combined with a fan provided optimal stroller cooling.

Retrofitting passive cooling strategies to combat heat stress in the face of climate change: A case study of a ready-made garment factory in Dhaka, Bangladesh.

The ready-made garment industry is critical to the Bangladesh economy. There is an urgent need to improve current working conditions and build capacity for heat mitigation as conditions worsen due to climate change. We modelled a typical, mid-sized, non-air-conditioned factory in Bangladesh and simulated how the indoor thermal environment is altered by four rooftop retrofits (1. extensive green roof, 2. rooftop shading, 3. white cool roof, 4. insulated white cool roof) on present-day and future decades under different climate scenarios. Simulations showed that all strategies reduce indoor air temperatures by around 2 °C on average and reduce the number of present-day annual work-hours during which wetbulb globe temperature exceeds the standardised limits for moderate work rates by up to 603 h - the equivalent of 75 (8 h) working days per year. By 2050 under a high-emissions scenario, indoor conditions with a rooftop intervention are comparable to present-day conditions. To reduce the growing need for carbon-intensive air-conditioning, sustainable heat mitigation strategies need to be incorporated into a wider range of solutions at the individual, building, and urban level. The results presented here have implications for factory planning and retrofit design, and may inform policies targeting worker health, well-being, and productivity.

Hot weather and heat extremes: health risks.

Hot ambient conditions and associated heat stress can increase mortality and morbidity, as well as increase adverse pregnancy outcomes and negatively affect mental health. High heat stress can also reduce physical work capacity and motor-cognitive performances, with consequences for productivity, and increase the risk of occupational health problems. Almost half of the global population and more than 1 billion workers are exposed to high heat episodes and about a third of all exposed workers have negative health effects. However, excess deaths and many heat-related health risks are preventable, with appropriate heat action plans involving behavioural strategies and biophysical solutions. Extreme heat events are becoming permanent features of summer seasons worldwide, causing many excess deaths. Heat-related morbidity and mortality are projected to increase further as climate change progresses, with greater risk associated with higher degrees of global warming. Particularly in tropical regions, increased warming might mean that physiological limits related to heat tolerance (survival) will be reached regularly and more often in coming decades. Climate change is interacting with other trends, such as population growth and ageing, urbanisation, and socioeconomic development, that can either exacerbate or ameliorate heat-related hazards. Urban temperatures are further enhanced by anthropogenic heat from vehicular transport and heat waste from buildings. Although there is some evidence of adaptation to increasing temperatures in high-income countries, projections of a hotter future suggest that without investment in research and risk management actions, heat-related morbidity and mortality are likely to increase.

Reducing the health effects of hot weather and heat extremes: from personal cooling strategies to green cities.

Heat extremes (ie, heatwaves) already have a serious impact on human health, with ageing, poverty, and chronic illnesses as aggravating factors. As the global community seeks to contend with even hotter weather in the future as a consequence of global climate change, there is a pressing need to better understand the most effective prevention and response measures that can be implemented, particularly in low-resource settings. In this Series paper, we describe how a future reliance on air conditioning is unsustainable and further marginalises the communities most vulnerable to the heat. We then show that a more holistic understanding of the thermal environment at the landscape and urban, building, and individual scales supports the identification of numerous sustainable opportunities to keep people cooler. We summarise the benefits (eg, effectiveness) and limitations of each identified cooling strategy, and recommend optimal interventions for settings such as aged care homes, slums, workplaces, mass gatherings, refugee camps, and playing sport. The integration of this information into well communicated heat action plans with robust surveillance and monitoring is essential for reducing the adverse health consequences of current and future extreme heat.

Influence of sex and biological maturation on the sudomotor response to exercise-heat stress: are girls disadvantaged?

Both adult females and children have been reported to have a lower sweating capacity and thus reduced evaporative heat loss potential that may increase their susceptibility to exertional hyperthermia in the heat. Compared with males, females have a lower maximal sweat rate and thus a theoretically lower maximum skin wettedness due to a lower sweat output per gland. Similarly, children have been suggested to be disadvantaged in high ambient temperatures due to a lower sweat production and therefore reduced evaporative capacity, despite modifications of heat transfer due to physical attributes and possible evaporative efficiency. The reported reductions in the sudomotor activity of females and children suggest a lower sweating capacity in girls. However, because of the complexities of isolating sex and maturation from the confounding effects of morphological differences (e.g., body surface area-to-mass ratio) and metabolic heat production, limited evidence exists supporting whether children, and, more specifically, girls are at a thermoregulatory disadvantage. Furthermore, a limited number of child-adult comparison studies involve females and very few studies have directly compared regional and whole body sudomotor activity between boys and girls. This minireview highlights the exercise-induced sudomotor response of females and children, summarizes previous research investigating the sudomotor response to exercise in girls, and suggests important areas for further research.

Exertional heat stroke in sport and the military: epidemiology and mitigation.

NEW FINDINGS: What is the topic of this review? Exertional heat stroke epidemiology in sport and military settings, along with common risk factors and strategies and policies designed to mitigate its occurrence. What advances does it highlight? Individual susceptibility to exertional heat stroke risk is dependent on the interaction of intrinsic and extrinsic factors. Heat policies in sport should assess environmental conditions, as well as the characteristics of the athlete, clothing/equipment worn and activity level of the sport. Exertional heat stroke risk reduction in the military should account for factors specific to training and personnel. ABSTRACT: Exertional heat illness occurs along a continuum, developing from the relatively mild condition of muscle cramps, to heat exhaustion, and in some cases to the life-threatening condition of heat stroke. The development of exertional heat stroke (EHS) is associated with an increase in core temperature stemming from inadequate heat dissipation to offset the rate of metabolically generated heat. Susceptibility to EHS is linked to the interaction of several factors including environmental conditions, individual characteristics, health conditions, medication and drug use, behavioural responses, and sport/organisational requirements. Two settings in which EHS is commonly observed are competitive sport and the military. In sport, the exact prevalence of EHS is unclear due to inconsistent exertional heat illness terminology, diagnostic criteria and data reporting. In contrast, exertional heat illness surveillance in the military is facilitated by standardised case definitions, a requirement to report all heat illness cases and a centralised medical record repository. To mitigate EHS risk, several strategies can be implemented by athletes and military personnel, including heat acclimation, ensuring adequate hydration, cold-water immersion and mandated work-to-rest ratios. Organisations may also consider developing sport or military task-specific heat stress policies that account for the evaporative heat loss requirement of participants, relative to the evaporative capacity of the environment. This review examines the epidemiology of EHS along with the strategies and policies designed to reduce its occurrence in sport and military settings. We highlight the nuances of identifying individuals at risk of EHS and summarise the benefits and shortcomings of various mitigation strategies.

The 2022 report of the MJA-Lancet Countdown on health and climate change: Australia unprepared and paying the price.

The MJA-Lancet Countdown on health and climate change in Australia was established in 2017 and produced its first national assessment in 2018 and annual updates in 2019, 2020 and 2021. It examines five broad domains: climate change impacts, exposures and vulnerability; adaptation, planning and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement. In this, the fifth year of the MJA-Lancet Countdown, we track progress on an extensive suite of indicators across these five domains, accessing and presenting the latest data and further refining and developing our analyses. Within just two years, Australia has experienced two unprecedented national catastrophes - the 2019-2020 summer heatwaves and bushfires and the 2021-2022 torrential rains and flooding. Such events are costing lives and displacing tens of thousands of people. Further, our analysis shows that there are clear signs that Australia's health emergency management capacity substantially decreased in 2021. We find some signs of progress with respect to health and climate change. The states continue to lead the way in health and climate change adaptation planning, with the Victorian plan being published in early 2022. At the national level, we note progress in health and climate change research funding by the National Health and Medical Research Council. We now also see an acceleration in the uptake of electric vehicles and continued uptake of and employment in renewable energy. However, we also find Australia's transition to renewables and zero carbon remains unacceptably slow, and the Australian Government's continuing failure to produce a national climate change and health adaptation plan places the health and lives of Australians at unnecessary risk today, which does not bode well for the future.

A sex/age anomaly in thermal comfort observed in an office worker field study: A menopausal effect?

In a field study conducted in office settings in Sydney, Australia, background survey and right-here-right-now thermal comfort questionnaires were collected from a sample of office workers. Indoor environmental observations, including air temperature, mean radiant temperature, air velocity, and relative humidity, were also recorded and matched with each questionnaire according to the time and location. During exploratory data analyses, we observed that female subjects aged over 40 and 50 or younger registered significantly warmer sensations than other subjects, male and female, from other age ranges. To further explore this phenomenon, the sample of building occupants was classified into two groups-women of perimenopausal age (over 40 and 50 or younger) while the remaining respondents served as a reference group for comparison. Women in the perimenopausal age range demonstrated an increased perception of warmth (p < 0.01) and expressed thermal dissatisfaction more frequently (p < 0.01) than the reference group respondents who were exposed to the same indoor environmental conditions. Furthermore, women of perimenopausal age also expressed preference for cooler thermal environments, that is, lower air temperature (p < 0.01) and greater air movement (p<0.01) than the reference group, and their thermal neutrality (ie, the room temperature corresponding to a neutral thermal sensation) was approximately 2°C cooler than that of the reference group (20.7°C vs 22.4°C). A potential physiological explanation for the distinct thermal perception of women aged over 40 and 50 or younger observed in this study could stem from menopausal symptoms-the presence of hot flushes and dysregulation of the thermoregulatory system.

Quantifying the impact of heat on human physical work capacity; part IV: interactions between work duration and heat stress severity.

High workplace temperatures negatively impact physical work capacity (PWC). Although PWC loss models with heat based on 1-h exposures are available, it is unclear if further adjustments are required to accommodate repeated work/rest cycles over the course of a full work shift. Therefore, we examined the impact of heat stress exposure on human PWC during a simulated work shift consisting of six 1-h work-rest cycles. Nine healthy males completed six 50-min work bouts, separated by 10-min rest intervals and an extended lunch break, on four separate occasions: once in a cool environment (15 °C/50% RH) and in three different air temperature and relative humidity combinations (moderate, 35 °C/50% RH; hot, 40 °C/50% RH; and very hot, 40 °C/70%). To mimic moderate to heavy workload, work was performed on a treadmill at a fixed heart rate of 130 beats·min-1. During each work bout, PWC was quantified as the kilojoules expended above resting levels. Over the shift, work output per cycle decreased, even in the cool climate, with the biggest decrement after the lunch break and meal consumption. Expressing PWC relative to that achieved in the cool environment for the same work duration, there was an additional 5(± 4)%, 7(± 6)%, and 16(± 7)% decrease in PWC when work was performed across a full work shift for the moderate, hot, and very hot condition respectively, compared with 1-h projections. Empirical models to predict PWC based on the level of heat stress (Wet-Bulb Globe Temperature, Universal Thermal Climate Index, Psychrometric Wet-Bulb Temperature, Humidex, and Heat Index) and the number of work cycles performed are presented.

Quantifying the impact of heat on human physical work capacity; part III: the impact of solar radiation varies with air temperature, humidity, and clothing coverage.

Heat stress decreases human physical work capacity (PWC), but the extent to which solar radiation (SOLAR) compounds this response is not well understood. This study empirically quantified how SOLAR impacts PWC in the heat, considering wide, but controlled, variations in air temperature, humidity, and clothing coverage. We also provide correction equations so PWC can be quantified outdoors using heat stress indices that do not ordinarily account for SOLAR (including the Heat Stress Index, Humidex, and Wet-Bulb Temperature). Fourteen young adult males (7 donning a work coverall, 7 with shorts and trainers) walked for 1 h at a fixed heart rate of 130 beats∙min-1, in seven combinations of air temperature (25 to 45°C) and relative humidity (20 or 80%), with and without SOLAR (800 W/m2 from solar lamps). Cumulative energy expenditure in the heat, relative to the work achieved in a cool reference condition, was used to determine PWC%. Skin temperature was the primary determinant of PWC in the heat. In dry climates with exposed skin (0.3 Clo), SOLAR caused PWC to decrease exponentially with rising air temperature, whereas work coveralls (0.9 Clo) negated this effect. In humid conditions, the SOLAR-induced reduction in PWC was consistent and linear across all levels of air temperature and clothing conditions. Wet-Bulb Globe Temperature and the Universal Thermal Climate Index represented SOLAR correctly and did not require a correction factor. For the Heat Stress Index, Humidex, and Wet-Bulb Temperature, correction factors are provided enabling forecasting of heat effects on work productivity.

Quantifying the impact of heat on human physical work capacity; part II: the observed interaction of air velocity with temperature, humidity, sweat rate, and clothing is not captured by most heat stress indices.

Increasing air movement can alleviate or exacerbate occupational heat strain, but the impact is not well defined across a wide range of hot environments, with different clothing levels. Therefore, we combined a large empirical study with a physical model of human heat transfer to determine the climates where increased air movement (with electric fans) provides effective body cooling. The model allowed us to generate practical advice using a high-resolution matrix of temperature and humidity. The empirical study involved a total of 300 1-h work trials in a variety of environments (35, 40, 45, and 50 °C, with 20 up to 80% relative humidity) with and without simulated wind (3.5 vs 0.2 m∙s-1), and wearing either minimal clothing or a full body work coverall. Our data provides compelling evidence that the impact of fans is strongly determined by air temperature and humidity. When air temperature is ≥ 35 °C, fans are ineffective and potentially harmful when relative humidity is below 50%. Our simulated data also show the climates where high wind/fans are beneficial or harmful, considering heat acclimation, age, and wind speed. Using unified weather indices, the impact of air movement is well captured by the universal thermal climate index, but not by wet-bulb globe temperature and aspirated wet-bulb temperature. Overall, the data from this study can inform new guidance for major public and occupational health agencies, potentially maintaining health and productivity in a warming climate.

Blunted sweating does not alter the rise in core temperature in people with multiple sclerosis exercising in the heat.

The purpose of this study is to determine whether thermoregulatory capacity is altered by multiple sclerosis (MS) during exercise in the heat. Sixteen MS participants (EDSS: 2.9 ± 0.9; 47 ± 8 yr; 77.6 ± 14.0 kg) and 14 healthy control (CON) participants (43 ± 11 yr; 78.6 ± 17.0 kg) cycled at a heat production of 4 W·kg-1 for 60 min at 30°C, 30% relative humidity (RH) (Warm). A subset of eight MS (EDSS: 2.6 ± 0.5; 44 ± 8 yr; 82.3 ± 18.2 kg) and 8 CON (44 ± 12 yr; 81.2 ± 21.1 kg) also exercised at 35°C, 30% RH (Hot). Rectal temperature (Tre), mean skin (Tsk) temperature, and local sweat rate (LSR) on the upper back (LSRback) and forearm (LSRarm) were measured. All CON, and only 9 of 16 and 7 of 8 MS participants completed 60 min of exercise in Warm and Hot trials, respectively. All MS participants who were unable to complete exercise stopped with a ΔTre between 0.2 and 0.5°C. The time to reach a ΔTre of 0.2°C was similar (MS: 28 ± 15 min, CON: 32 ± 18 min; P = 0.51). For MS participants, completing 60-min of exercise in Warm, ΔTre (P = 0.13), ΔTsk (P = 0.45), LSRback (P = 0.69), and LSRarm (P = 0.54) was similar to CON, but ΔTb (body temperature) (MS: 0.16 ± 0.13°C, CON: 0.07 ± 0.06°C; P = 0.02) and onset time (MS: 16 ± 10 min, CON: 8 ± 5 min; P = 0.02) for sweating were greater in MS. Similarly, in Hot, ΔTre (P = 0.52), ΔTsk (P = 0.06), LSRback (P = 0.59), and LSRarm (P = 0.08) were similar, but ΔTb (MS: 0.19 ± 0.16°C, CON: 0.06 ± 0.04°C; P = 0.04) and onset time (MS: 13 ± 7 min, CON: 6 ± 3 min; P = 0.02) for sweating were greater in MS. Even at 35°C, a delayed sweating onset did not alter heat loss to sufficiently affect exercise-induced rises in core temperature. Heat intolerance with MS does not seem attributable to thermoregulatory impairments.

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

NEW FINDINGS: What is the central question of this study? Are fitness-related improvements in thermoregulatory responses during uncompensable heat stress mediated by aerobic capacity V̇O2max or is it the partial heat acclimation associated with training? What is the main finding and its importance? During uncompensable heat stress, individuals with high and low V̇O2max displayed similar sweating and core temperature responses whereas exercise training in previously untrained individuals resulted in a greater sweat rate and a smaller rise in core temperature. These observations suggest that it is training, not V̇O2max per se, that mediates thermoregulatory improvements during uncompensable heat stress. ABSTRACT: It remains unclear whether aerobic fitness, as defined by the maximum rate of oxygen consumption V̇O2max , independently improves heat dissipation in uncompensable environments, or whether the thermoregulatory adaptations associated with heat acclimation are due to repeated bouts of exercise-induced heat stress during regular aerobic training. The present analysis sought to determine if V̇O2max independently influences thermoregulatory sweating, maximum skin wettedness (ωmax ) and the change in rectal temperature (ΔTre ) during 60 min of exercise in an uncompensable environment (37.0 ± 0.8°C, 4.0 ± 0.2 kPa, 64 ± 3% relative humidity) at a fixed rate of heat production per unit mass (6 W kg-1 ). Retrospective analyses were performed on 22 participants (3 groups), aerobically unfit (UF; n = 7; V̇O2max : 41.7 ± 9.4 ml kg-1  min-1 ), aerobically fit (F; n = 7; V̇O2max : 55.6 ± 4.3 ml kg-1  min-1 ; P < 0.01) and aerobically unfit (n = 8) individuals, before (pre; V̇O2max : 45.8 ± 11.6 ml kg-1  min-1 ) and after (post; V̇O2max : 52.0 ± 11.1 ml kg-1  min-1 ; P < 0.001) an 8-week training intervention. ωmax was similar between UF (0.74 ± 0.09) and F (0.78 ± 0.08, P = 0.22). However, ωmax was greater post- (0.84 ± 0.08) compared to pre- (0.72 ± 0.06, P = 0.02) training. During exercise, mean local sweat rate (forearm and upper-back) was greater post- (1.24 ± 0.20 mg cm-2  min-1 ) compared to pre- (1.04 ± 0.25 mg cm-2  min-1 , P < 0.01) training, but similar between UF (0.94 ± 0.31 mg cm-2  min-1 , P = 0.90) and F (1.02 ± 0.30 mg cm-2  min-1 ). The ΔTre at 60 min of exercise was greater pre- (1.13 ± 0.16°C, P < 0.01) compared to post- (0.96 ± 0.14°C) training, but similar between UF (0.85 ± 0.29°C, P = 0.22) and F (0.95 ± 0.22°C). Taken together, aerobic training, not V̇O2max per se, confers an increased ωmax , greater sweat rate, and smaller rise in core temperature during uncompensable heat stress in fit individuals.

Normobaric hypoxia does not alter the critical environmental limits for thermal balance during exercise-heat stress.

NEW FINDINGS: What is the central question of this study? Hypoxia reportedly does not impair thermoregulation during exercise in compensable heat stress conditions: does it have an impact on maximal heat dissipation and therefore the critical environmental limit for the physiological compensability of core temperature? What is the main finding and its importance? Although skin blood flow was higher in hypoxia, no differences in sweat rates or the critical environmental limit for the physiological compensability of core temperature - an indicator of maximal heat loss - were found compared to exercise in normoxia, indicating no influence of normobaric hypoxia on thermoregulatory capacity in warm conditions. ABSTRACT: Altered control of skin blood flow (SkBF) in hypoxia does not impair thermoregulation during exercise in compensable conditions, but its impact on maximal heat dissipation is unknown. This study therefore sought to determine whether maximum heat loss is altered by hypoxia during exercise in warm conditions. On separate days, eight males exercised for 90 min at a fixed heat production of ∼500 W in normoxia (NORM) or normobaric hypoxia (HYP, FIO2  = 0.13) in a 34°C environment. Ambient vapour pressure was maintained at 2.13 kPa for 45 min, after which it was raised 0.11 kPa every 7.5 min. The critical ambient vapour pressure at which oesophageal temperature inflected upward (Pcrit ) indicated that maximum heat dissipation had been reached. Neither local sweat rates on the upper arm, back and forehead (average NORM: 1.46 (0.15) vs. HYP: 1.41 (0.16) mg cm-2  min-1 ; P = 0.59) nor whole-body sweat losses (NORM: 1029 (137) g vs. HYP: 1025 (150) g; P = 0.95) were different between trials. Laser-Doppler flux values (LDF; arbitrary units), an index of SkBF, were not different between NORM and HYP on the forearm (P = 0.23) or back (P = 0.73); however, when normalized as a percentage of maximum, LDF values tended to be higher in HYP compared to NORM at the forearm (condition effect, P = 0.05) but not back (P = 0.19). Despite potentially greater SkBF in hypoxia, there was no difference in Pcrit between conditions (NORM: 3.67 (0.35) kPa; HYP: 3.46 (0.39) kPa; P = 0.22). These findings suggest that hypoxia does not independently alter thermoregulatory capacity during exercise in warm conditions.

The 2021 report of the MJA-Lancet Countdown on health and climate change: Australia increasingly out on a limb.

The MJA-Lancet Countdown on health and climate change in Australia was established in 2017, and produced its first national assessment in 2018, its first annual update in 2019, and its second annual update in 2020. It examines indicators across five broad domains: climate change impacts, exposures and vulnerability; adaptation, planning and resilience for health; mitigation actions and health co-benefits; economics and finance; and public and political engagement. Our special report in 2020 focused on the unprecedented and catastrophic 2019-20 Australian bushfire season, highlighting indicators that explore the relationships between health, climate change and bushfires. For 2021, we return to reporting on the full suite of indicators across each of the five domains and have added some new indicators. We find that Australians are increasingly exposed to and vulnerable to excess heat and that this is already limiting our way of life, increasing the risk of heat stress during outdoor sports, and decreasing work productivity across a range of sectors. Other weather extremes are also on the rise, resulting in escalating social, economic and health impacts. Climate change disproportionately threatens Indigenous Australians' wellbeing in multiple and complex ways. In response to these threats, we find positive action at the individual, local, state and territory levels, with growing uptake of rooftop solar and electric vehicles, and the beginnings of appropriate adaptation planning. However, this is severely undermined by national policies and actions that are contrary and increasingly place Australia out on a limb. Australia has responded well to the COVID-19 public health crisis (while still emerging from the bushfire crisis that preceded it) and it now needs to respond to and prepare for the health crises resulting from climate change.