Physical Activity Dependence on Relative Temperature and Humidity Characteristics in a Young, Insufficiently Active Population: A Weather Typing Analysis

BACKGROUND

Physical activity (PA) is an important contributor to one's physical and mental health both acutely and across the lifespan. Much research has done on the ambient environment's impact on PA; however, these studies have used absolute values of atmospheric measures such as temperature and humidity, which vary spatiotemporally and make comparisons between studies which differ in location or time of year difficult to square with one another.

METHODS

Here, we employ the Global Weather Type Classification, Version 2, to determine the combined impact of temperature and humidity on PA in a sample of insufficiently active young adults. We conducted secondary analyses of data from a single-group behavioral intervention trial that varied the number of digital messages sent daily. Young adults (n = 81) wore Fitbit Versa smartwatches for a 6-month period sometime between April 2019 and July 2020, and location was tracked using a custom smartphone application.

RESULTS

Mixed linear models indicated that, across 8179 person-days, PA was significantly lower on days with humid conditions and significantly higher on warm dry days, though the latter relationship was no longer significant when controlling for timing in relation to the COVID-19 pandemic declaration. Demographic factors did not affect the relationship between weather and PA.

CONCLUSIONS

Results are a first step in providing additional guidance for encouraging PA in insufficiently active individuals given forecasted daily weather conditions. Future work should examine seasonal variability in the weather type-PA relationship without the influence of a world-altering event influencing results.

Heat stress vulnerability and critical environmental limits for older adults

The present study examined heat stress vulnerability of apparently healthy older vs. young adults and characterized critical environmental limits for older adults in an indoor setting at rest (Rest) and during minimal activity associated with activities of daily living. Critical environmental limits are combinations of ambient temperature and humidity above which heat balance cannot be maintained (i.e., becomes uncompensable) for a given metabolic heat production. Here we exposed fifty-one young (23±4 yrs) and 49 older (71±6 yrs) adults to progressive heat stress across a wide range of environments in an environmental chamber during Minimal Activity (young and older subjects) and Rest (older adults only). Heat compensability curves were shifted leftward for older adults indicating age-dependent heat vulnerablity (p < 0.01). During Minimal Activity, critical environmental limits were lower in older compared to young adults (p < 0.0001) and lower than those at Rest (p < 0.0001). These data document heat vulnerability of apparently healthy older adults and to define critical environmental limits for indoor settings in older adults at rest and during activities of daily living, and can be used to develop evidence-based recommendations to minimize the deleterious impacts of extreme heat events in this population.

Greatly enhanced risk to humans as a consequence of empirically determined lower moist heat stress tolerance

As heatwaves become more frequent, intense, and longer-lasting due to climate change, the question of breaching thermal limits becomes pressing. A wet-bulb temperature (Tw) of 35 °C has been proposed as a theoretical upper limit on human abilities to biologically thermoregulate. But, recent-empirical-research using human subjects found a significantly lower maximum Tw at which thermoregulation is possible even with minimal metabolic activity. Projecting future exposure to this empirical critical environmental limit has not been done. Here, using this more accurate threshold and the latest coupled climate model results, we quantify exposure to dangerous, potentially lethal heat for future climates at various global warming levels. We find that humanity is more vulnerable to moist heat stress than previously proposed because of these lower thermal limits. Still, limiting warming to under 2 °C nearly eliminates exposure and risk of widespread uncompensable moist heatwaves as a sharp rise in exposure occurs at 3 °C of warming. Parts of the Middle East and the Indus River Valley experience brief exceedances with only 1.5 °C warming. More widespread, but brief, dangerous heat stress occurs in a +2 °C climate, including in eastern China and sub-Saharan Africa, while the US Midwest emerges as a moist heat stress hotspot in a +3 °C climate. In the future, moist heat extremes will lie outside the bounds of past human experience and beyond current heat mitigation strategies for billions of people. While some physiological adaptation from the thresholds described here is possible, additional behavioral, cultural, and technical adaptation will be required to maintain healthy lifestyles.

Adverse heat-health outcomes and critical environmental limits (Pennsylvania State University Human Environmental Age Thresholds project)

BACKGROUND

The earth's climate is warming and the frequency, duration, and severity of heat waves are increasing. Meanwhile, the world's population is rapidly aging. Epidemiological data demonstrate exponentially greater increases in morbidity and mortality during heat waves in adults ≥65 years. Laboratory data substantiate the mechanistic underpinnings of age-associated differences in thermoregulatory function. However, the specific combinations of environmental conditions (i.e., ambient temperature and absolute/relative humidity) above which older adults are at increased risk of heat-related morbidity and mortality are less clear.

METHODS

This review was conducted to (1) examine the recent (past 3 years) literature regarding heat-related morbidity and mortality in the elderly and discuss projections of future heat-related morbidity and mortality based on climate model data, and (2) detail the background and unique methodology of our ongoing laboratory-based projects aimed toward identifying the specific environmental conditions that result in elevated risk of heat illness in older adults, and the implications of using the data toward the development of evidence-based safety interventions in a continually-warming climate (PSU HEAT; Human Environmental Age Thresholds).

RESULTS

The recent literature demonstrates that extreme heat continues to be increasingly detrimental to the health of the elderly and that this is apparent across the world, although the specific environmental conditions above which older adults are at increased risk of heat-related morbidity and mortality remain unclear.

CONCLUSION

Characterizing the environmental conditions above which risk of heat-related illnesses increase remains critical to enact policy decisions and mitigation efforts to protect vulnerable people during extreme heat events.

Core temperature responses to compensable versus uncompensable heat stress in young adults (PSU HEAT Project)

With global warming, much attention has been paid to the upper limits of human adaptability. However, the time to reach a generally accepted core temperature criterion (40.2°C) associated with heat-related illness above (uncompensable heat stress) and just below (compensable heat stress) the upper limits for heat balance remains unclear. Forty-eight (22 men/26 women; 23 ± 4 yr) subjects were exposed to progressive heat stress in an environmental chamber during minimal activity (MinAct, 159 ± 34 W) and light ambulation (LightAmb, 260 ± 55 W) in warm-humid (WH; ∼35°C, >60% RH) and hot-dry (HD; 43°C-48°C, <25% RH) environments until heat stress became uncompensable. For each condition, we compared heat storage (S) and the change in gastrointestinal temperature (ΔTgi) over time during compensable and uncompensable heat stress. In addition, we examined whether individual characteristics or seasonality were associated with the rate of increase in Tgi. During compensable heat stress, S was higher in HD than in WH environments (P < 0.05) resulting in a greater but more variable ΔTgi (P ≥ 0.06) for both metabolic rates. There were no differences among conditions during uncompensable heat stress (all P > 0.05). There was no influence of sex, aerobic fitness, or seasonality, but a larger body size was associated with a greater ΔTgi during LightAmb in WH (P = 0.003). The slopes of the Tgi response during compensable (WH: MinAct, 0.06, LightAmb, 0.09; HD: MinAct, 0.12, LightAmb, 0.15°C/h) and uncompensable (WH: MinAct, 0.74, LightAmb, 0.87; HD: MinAct, 0.71, LightAmb, 0.93°C/h) heat stress can be used to estimate the time to reach a target core temperature from any given starting value.NEW & NOTEWORTHY This study is the first to examine heat storage and the rate of change in core temperature above (uncompensable heat stress) and just below (compensable heat stress) critical environmental limits to human heat balance. Furthermore, we examine the influence of individual subject characteristics and seasonality on the change in core temperature in warm-humid versus hot-dry environments. We provide the rate of change in core temperature, enabling projections to be made to and from any hypothetical core temperature.

Utility of the Heat Index in defining the upper limits of thermal balance during light physical activity (PSU HEAT Project)

Extreme heat events and consequent detrimental heat-health outcomes have been increasing in recent decades and are expected to continue with future climate warming. While many indices have been created to quantify the combined atmospheric contributions to heat, few have been validated to determine how index-defined heat conditions impact human health. However, this subset of indices is likely not valid for all situations and populations nor easily understood and interpreted by health officials and the public. In this study, we compare the ability of thresholds determined from the National Weather Service's (NWS) Heat Index (HI), the Wet Bulb Globe Temperature (WBGT), and the Universal Thermal Climate Index (UTCI) to predict the compensability of human heat stress (upper limits of heat balance) measured as part of the Pennsylvania State University's Heat Environmental Age Thresholds (PSU HEAT) project. While the WBGT performed the best of the three indices for both minimal activities of daily living (MinAct; 83 W·m-2) and light ambulation (LightAmb; 133 W·m-2) in a cohort of young, healthy subjects, HI was likewise accurate in predicting heat stress compensability in MinAct conditions. HI was significantly correlated with subjects' perception of temperature and humidity as well as their body core temperature, linking perception of the ambient environment with physiological responses in MinAct conditions. Given the familiarity the public has with HI, it may be better utilized in the expansion of safeguard policies and the issuance of heat warnings during extreme heat events, especially when access to engineered cooling strategies is unavailable.

Critical environmental limits for young, healthy adults (PSU HEAT Project)

Critical environmental limits are those combinations of ambient temperature and humidity above which heat balance cannot be maintained for a given metabolic heat production, limiting exposure time, and placing individuals at increased risk of heat-related illness. The aim of this study was to establish those limits in young (18-34 yr) healthy adults during low-intensity activity approximating the metabolic demand of activities of daily living. Twenty-five (12 men/13 women) subjects were exposed to progressive heat stress in an environmental chamber at two rates of metabolic heat production chosen to represent minimal activity (MinAct) or light ambulation (LightAmb). Progressive heat stress was performed with either 1) constant dry-bulb temperature (T_db) and increasing ambient water vapor pressure (P_a) (P_crit trials; 36°C, 38°C, or 40°C) or 2) constant P_a and increasing T_db (T_crit trials; 12, 16, or 20 mmHg). Each subject was tested during MinAct and LightAmb in two to three experimental conditions in random order, for a total of four to six trials per participant. Higher metabolic heat production (P < 0.001) during LightAmb compared with MinAct trials resulted in significantly lower critical environmental limits across all P_crit and T_crit conditions (all P < 0.001). These data, presented graphically herein on a psychrometric chart, are the first to define critical environmental limits for young adults during activity resembling those of light household tasks or other activities of daily living and can be used to develop guidelines, policy decisions, and evidence-based alert communications to minimize the deleterious impacts of extreme heat events.NEW & NOTEWORTHY Critical environmental limits are those combinations of temperature and humidity above which heat balance cannot be maintained, placing individuals at increased risk of heat-related illness. Those limits have been investigated in young adults during exercise at 30% V̇o_2max, but not during metabolic rates that approximate those of light activities of daily living. Herein, we establish critical environmental limits for young adults at two metabolic rates that reflect activities of daily living and leisurely walking.

Evaluating the 35°C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project)

A wet-bulb temperature of 35°C has been theorized to be the limit to human adaptability to extreme heat, a growing concern in the face of continued and predicted accelerated climate change. Although this theorized threshold is based in physiological principles, it has not been tested using empirical data. This study examined the critical wet-bulb temperature (T_wb,crit) at which heat stress becomes uncompensable in young, healthy adults performing tasks at modest metabolic rates mimicking basic activities of daily life. Across six experimentally determined environmental limits, no subject's T_wb,crit reached the 35°C limit and all means were significantly lower than the theoretical 35°C threshold. Mean T_wb,crit values were relatively constant across 36°C -40°C humid environments and averaged 30.55 ± 0.98°C but progressively decreased (higher deviation from 35°C) in hotter, dry ambient environments. T_wb,crit was significantly associated with mean skin temperature (and a faster warming rate of the skin) due to larger increases in dry heat gain in the hot-dry environments. As sweat rates did not significantly differ among experimental environments, evaporative cooling was outpaced by dry heat gain in hot-dry conditions, causing larger deviations from the theoretical 35°C adaptability threshold. In summary, a wet-bulb temperature threshold cannot be applied to human adaptability across all climatic conditions and where appropriate (high humidity), that threshold is well below 35°C.NEW & NOTEWORTHY This study is the first to use empirical physiological observations to examine the well-publicized theoretical 35°C wet-bulb temperature limit for human to extreme environments. We find that uncompensable heat stress in humid environments occurs in young, healthy adults at wet-bulb temperatures significantly lower than 35°C. In addition, uncompensable heat stress occurs at widely different wet-bulb temperatures as a function of ambient vapor pressure.

The role of outdoor microclimatic features at long-term care facilities in advancing the health of its residents: An integrative review and future strategies

Projections show that Earth's climate will continue to warm concurrent with increases in the percentage of the world's elderly population. With an understanding that the body's resilience to the heat degrades as it ages, these coupled phenomena point to serious concerns of heat-related mortality in growing elderly populations. As many of the people in this age cohort choose to live in managed long-term care facilities, it's imperative that outdoor spaces of these communities be made thermally comfortable so that connections with nature and the promotion of non-sedentary activities are maintained. Studies have shown that simply being outside has a positive impact on a broad range of the psychosocial well-being of older adults. However, these spaces must be designed to afford accessibility, safety, and aesthetically pleasing experiences so that they are taken full advantage of. Here, we employ an integrative review to link ideas from the disciplines of climate science, health and physiology, and landscape architecture to explain the connections between heat, increased morbidity and mortality in aging adults, existing gaps in thermal comfort models, and key strategies in the development of useable, comfortable outdoor spaces for older adults. Integrative reviews allow for new frameworks or perspectives on a subject to be introduced. Uncovering the synergy of these three knowledge bases can contribute to guiding microclimatic research, design practitioners, and care providers as they seek safe, comfortable and inviting outdoor spaces for aging adults.

Reimagining spaces where children play: developing guidance for thermally comfortable playgrounds in Canada

Setting

Planning and designing thermally comfortable outdoor spaces is increasingly important in the context of climate change, particularly as children are more vulnerable than adults to environmental extremes. However, existing playground standards focus on equipment and surfacing to reduce acute injuries, with no mention of potential negative health consequences related to heat illness, sun exposure, and other thermal extremes. The goal of this project was to develop proposed guidelines for designing thermally comfortable playgrounds in Canada for inclusion within the CAN/CSA-Z614 Children’s playground equipment and surfacing standard.

Intervention

The project to develop guidance for thermally comfortable playgrounds was initiated with a municipal project in Windsor, Ontario, to increase shade, vegetation, and water features at parks and playgrounds to provide more comfortable experiences amid the increased frequency of hot days (≥30°C). The lack of available information to best manage environmental conditions led to a collaborative effort to build resources and raise awareness of best practices in the design of thermally comfortable playgrounds.

Outcomes

A group of multidisciplinary experts developed technical guidance for improving thermal comfort at playgrounds, including a six-page thermal comfort annex adopted within a national playground and equipment standard. The annex has been used by Canadian schools in a competition to design and implement green playgrounds.

Implications

Both the technical report and the thermal comfort annex provide increased awareness and needed guidance for managing environmental conditions at playgrounds. Thermally safe and comfortable play spaces will help ensure that Canada’s playgrounds are designed to minimize environmental health risks for children.

Improved methods for estimating mean radiant temperature in hot and sunny outdoor settings

Thermal comfort research has utilized various sensors and models to estimate the mean radiant temperature (MRT) experienced by a human, including the standard black globe thermometer (SGT), acrylic globe thermometers (AGT), and cylindrical radiation thermometers (CRT). Rather than directly measuring radiation, a temperature is measured in the center of these low-cost sensors that can be related to MRT after theoretically accounting for convection. However, these sensors have not been systematically tested under long-term hot and clear conditions. Further, under variable weather conditions, many issues can arise due to slow response times, shape, inaccuracies in material properties and assumptions, and color (albedo, emissivity) inconsistencies. Here, we assess the performance of MRT produced by various heat transfer models, with and without new average surface temperature ([Formula: see text]) correction factors, using five instruments-the SGT (15 cm, black), tan and black CRTs, gray and black 38 mm AGTs-compared to 3D integral radiation measurements. Measurements were taken on an unobscured roof throughout summer-to-early-fall months in Tempe, Arizona, examining 58 full-sun days. Deviations without correcting for asymmetrical surface heating-found to be the main cause of errors-reached ± 15-20 °C MRT. By accounting for asymmetric heating through [Formula: see text] calculations, new corrective algorithms were derived for the low-cost sensor models. Results show significant improvements in the estimated MRT error for each sensor (i.e., ∆MRT_{model - IRM}) when applying the [Formula: see text] corrections. The tan MRT_CRT improved from 1.9 ± 6.2 to -0.1 ± 4.4 °C, while the gray AGT and SGT showed improvements from -1.6 ± 7.2 to -0.4 ± 6.3 °C and - 6.6 ± 6.4 to - 0.03 ± 5.7 °C, respectively. The new corrections also eliminated dependence on other meteorological factors (zenith, wind speed). From these results, we provide three simple equations for CRT, AGT, and SGT correction for future research use under warm-hot and clear conditions. This study is the most comprehensive empirical assessment of various low-cost instruments with broad applicability in urban climate and biometeorological research.

Investigating the culturable atmospheric fungal and bacterial microbiome in West Texas: implication of dust storms and origins of the air parcels

Individuals often experience ailments such as allergies, asthma and respiratory tract infections throughout the year. Weather reports often include estimations of common allergens that can affect these individuals. To describe the local 'atmospheric microbiome' in Lubbock, Texas, USA, we examined the culturable fungal and bacterial microbiome present in the air on calm and dust storm days using internal transcribed spacer (ITS)-1 and 16S rRNA amplicon sequencing, respectively. While some types of airborne fungi were frequently present throughout the year, distinct differences were also observed between calm and dust storm days. We also observed the influence of the origin of air parcels and wind elevation of the air trajectory. The most abundant genera of fungi identified during the study period were Cryptococcus, Aureobasidium, Alternaria, Cladosporium and Filobasidium. This observation was not surprising considering the agricultural intensive environment of West Texas. Interestingly, Cladosporium, a common allergenic mold, was increased during days with dust storm events. The predominant bacterial genera observed were Bacillus, Pseudomonas, Psychrobacter, Massilia and Exiguobacterium. The relative abundance of the psychrophiles, Psychrobacter and Exiguobacterium, was surprising, given the semi-aridity of West Texas. Coupling our observations with back trajectories of the wind (Hybrid Single-Particle Lagrangian Integrated Trajectory models) demonstrated that dust storms, regional anthropogenic activity and origin of air parcels are important influences on the diversity and temporal presence of the atmospheric microbiome.

Workplace heat exposure, health protection, and economic impacts: A case study in Canada

BACKGROUND

Occupational heat exposure is a serious concern for worker health, productivity, and the economy. Few studies in North America assess how on-site wet bulb globe temperature (WBGT) levels and guidelines are applied in practice.

METHODS

We assessed the use of a WBGT sensor for localized summertime heat exposures experienced by outdoor laborers at an industrial worksite in Ontario, Canada during the warm season (May-October) from 2012 to 2018 inclusive. We further examined informed decision making, approximated workers' predicted heat strain (sweat loss, core temperature), and estimated potential financial loss (via hourly wages) due to decreased work allowance in the heat.

RESULTS

Significantly higher worksite WBGT levels occured compared with regional levels estimated at the airport, with an upward trend in heat warnings over the 7 years and expansion of warnings into the fall season. The maximum WBGT during warnings related strongly to predicted hourly sweat loss. On average, 22 hours per worker were lost each summer (~1% of annual work hours) as a result of taking breaks or stopping due to heat. This amount of time corresponded to an average individual loss of C$1100 Canadian dollars (~C$220,000 combined for ~200 workers) to workers or the company. The additional losses for an enterprise due to reduced product output were not estimated.

CONCLUSIONS

Worksite observations and actions at the microscale are essential for improving the estimates of health and economic costs of extreme heat to enterprises and society. Providing worksite heat metrics to the employees aids in appropriate decision making and health protection.

Short communication: trends in biometeorology publishing: a case study of climate and Human Health Commission members

The International Journal of Biometeorology (IJB) has been the flagship journal in the field for the past 60+ years. However, given its interdisciplinary nature, biometeorology research has appeared in numerous publication outlets other than the IJB. This study compiles the most popular of these journals, so that early-career biometeorologists might be able to be exposed to more literature that the field has to offer. In focusing on where members of the International Society of Biometeorology's (ISB) Climate and Human Health Commission (CHH) members publish, journals with a general focus on fields such as climate, the environment, and health stand out. Many of these journals have impact factors much higher than the IJB, potentially making them more attractive for dissemination of results to a larger audience. With this paper, the authors hope that the interest in biometeorology is broadened through an expansion of known available literature, specifically with early-career researchers.

The effects of synoptic weather on influenza infection incidences: a retrospective study utilizing digital disease surveillance

The environmental drivers and mechanisms of influenza dynamics remain unclear. The recent development of influenza surveillance--particularly the emergence of digital epidemiology--provides an opportunity to further understand this puzzle as an area within applied human biometeorology. This paper investigates the short-term weather effects on human influenza activity at a synoptic scale during cold seasons. Using 10 years (2005-2014) of municipal level influenza surveillance data (an adjustment of the Google Flu Trends estimation from the Centers for Disease Control's virologic surveillance data) and daily spatial synoptic classification weather types, we explore and compare the effects of weather exposure on the influenza infection incidences in 79 cities across the USA. We find that during the cold seasons the presence of the polar [i.e., dry polar (DP) and moist polar (MP)] weather types is significantly associated with increasing influenza likelihood in 62 and 68% of the studied cities, respectively, while the presence of tropical [i.e., dry tropical (DT) and moist tropical (MT)] weather types is associated with a significantly decreasing occurrence of influenza in 56 and 43% of the cities, respectively. The MP and the DP weather types exhibit similar close positive correlations with influenza infection incidences, indicating that both cold-dry and cold-moist air provide favorable conditions for the occurrence of influenza in the cold seasons. Additionally, when tropical weather types are present, the humid (MT) and the dry (DT) weather types have similar strong impacts to inhibit the occurrence of influenza. These findings suggest that temperature is a more dominating atmospheric factor than moisture that impacts the occurrences of influenza in cold seasons.

Supporting sustainability initiatives through biometeorology education and training

The International Society of Biometeorology (ISB) has covered significant breadth and depth addressing fundamental and applied societal and environmental challenges in the last 60 years. Biometeorology is an interdisciplinary science connecting living organisms to their environment, but there is very little understanding of the existence and placement of this discipline within formal educational systems and institutions. It is thus difficult to project the ability of members of the biometeorological community-especially the biometeorologists of the future-to help solve global challenges. In this paper, we ask: At present, how we are training people to understand and think about biometeorology? We also ask: What are the current tools and opportunities in which biometeorologists might address future challenges? Finally, we connect these two questions by asking: What type of new training and skill development is needed to better educate "biometeorologists of the future" to more effectively address the future challenges? To answer these questions, we provide quantitative and qualitative evidence from an educationally focused workshop attended by new professionals in biometeorology. We identify four common themes (thermal comfort and exposures, agricultural productivity, air quality, and urbanization) that biometeorologists are currently studying and that we expect to be important in the future based on their alignment with the United Nations Sustainable Development Goals. Review of recent literature within each of these thematic areas highlights a wide array of skill sets and perspectives that biometeorologists are already using. Current and new professionals within the ISB have noted highly varying and largely improvised educational pathways into the field. While variability and improvisation may be assets in promoting flexibility, adaptation, and interdisciplinarity, the lack of formal training in biometeorology raises concerns about the extent to which continuing generations of scholars will identify and engage with the community of scholarship that the ISB has developed over its 60-year history.