Moving in a hotter world: Maintaining adequate childhood fitness as a climate change countermeasure

Abstract

Children cope with high temperatures differently than adults do, largely because of slight alterations in their body proportions and heat loss mechanisms compared to fully mature humans. Paradoxically, all current tools of assessing thermal strain have been developed on adults. As the Earth's warming continues to accelerate, children are set to bear the health risk brunt of rising global temperatures. Physical fitness has a direct impact on heat tolerance, yet children are less fit and more obese than ever before. Longitudinal research reveals that children have 30% lower aerobic fitness than their parents did at the same age; this deficit is greater than can be recovered by training alone. So, as the planet's climate and weather patterns become more extreme, children may become less capable of tolerating it. This comprehensive review provides an outline of child thermoregulation and assessment of thermal strain, before moving to summarize how aerobic fitness can modulate hyperthermia, heat tolerance, and behavioral thermoregulation in this under-researched population. The nature of child physical activity, physical fitness, and one's physical literacy journey as an interconnected paradigm for promoting climate change resilience is explored. Finally, future research foci are suggested to encourage continued exploration of this dynamic field, notable since more extreme, multifactorial environmental stressors are expected to continue challenging the physiological strain of the human population for the foreseeable future.

Keywords: Children; behavioral thermoregulation; environmental epidemiology; exercise; heat stress; physical activity; tolerance.

Figure 1.

Climate change impacts on human health. The effects of climate change will exert both direct and indirect outcomes on human health, which may seriously affect the 24-hour movement behavior patterns of people. One example outlined here pertains to the COVID-19 pandemic outbreak, resulting from the introduction of a novel coronavirus pathogen to the human species with concomitantly strong mitigation measures aimed at reducing virus spread. However, these societal measures also directly impacted billions of people’s ability to move freely, causing significant barriers to remain physically active. These rapidly evolving measures are not conducive to maintaining adequate or optimal health over the past 2 y. Remaining confined for days, weeks, or sometimes months on end can significantly impair one’s mental health, affect respiratory health, and may place certain individuals at greater risk of suffering heat illness, especially if confinement periods coincide with extreme weather events. Similar negative feedback loops may occur as a result from direct (e.g. flooding, wildfire, heat), or indirect (e.g. air pollution, seasonal allergy severity) climate change effects further exacerbating negative 24-hour movement behaviors.

Figure 2.

Mechanisms of heat exchange in children. The ability to maintain heat balance (S) relies on an individual’s metabolic storage (M), their external work rate (W), radiative (R), convective (C), conductive (K), and evaporative (E) heat exchange. Children’s (supposedly) decreased heat storage capacity compared to adults means they are more reliant on so-called “dry” mechanisms of heat exchange (conduction, convection) to maintain heat balance.

Figure 3.

Simplified schematic of conflicts arising within the cardiovascular system during continued heat exposure and exercise. Serious physiological consequences to increased heat load can include hyperthermia, endotoxemia, cerebral hypoxia, and potentially death, in extreme cases. The dashed box depicts physiological responses that can occur during exertional heat stress, although at what point normal responses to heat turn to clinically problematic levels of heat illness will depend on many factors, including (but not limited to) some highlighted in the “modifiers” box listed on the left-hand side of this figure. Certain functions which occur normally in response to exercising in a hot environment, (and are necessary for stimulating positive heat acclimation processes) are depicted above the dashed line, but at a certain point, the heat strain accrued can become a clinical concern. Blue downward arrows indicate a factor which may be downregulated or less impactful in children, whereas red upward arrows indicate a factor which children may experience to greater extent relative to fully mature humans. Abbreviations: CO, cardiac output; BF, blood flow; PBF, peripheral blood flow; PBV, peripheral blood volume; TBV, total blood volume; CBV, central blood volume; CVP, central venous pressure; V, volume; Tc, core temperature; Tsk, skin temperature.

Figure 4.

Skin temperature as a modulator of core temperature. When humans are given the opportunity to behaviorally thermoregulate, they may choose from a variety of activities that can directly affect skin temperature, which in turn (eventually) modifies core temperature. However, it is not known to what extent (i.e. how powerful) behavioral thermoregulation affects temperature regulation in children, especially young ones who may be dependent on supervisory control. This is a health risk concern, especially since prepubescent children who are under heat stress see changes in skin blood flow to a relatively greater extent than fully mature humans. Children may therefore experience greater (or sometimes lesser) thermal strain to a given environment compared to adults. They may also not be aware of how they are feeling when moving in a hot environment.

Figure 5.

Physical Literacy model with a feed-forward physical domain. Physical literacy is comprised of several components which include the physical, cognitive, emotional, and social domains. Acquiring motor skills results in physical fitness; being more physically fit allows children to learn new skills more easily, creating a powerful feed-forward positive relationship that itself feeds into the physical literacy model, affecting each of the other three domains, respectively.

Figure 6.

Integrated model of physical activity, fitness, and literacy within the 24-hour movement behavior and climate change context. Maintaining adequate physical activity ensures there is a foundational groundwork of physical readiness which will be necessary to produce basic resistance and mitigation against degrading 24-hour movement behaviors brought on by the direct or indirect factors associated with climate change, some of which include direct warming, novel disease vectors, wildfire, air pollution, increased aeroallergens, and more. Overall physical activity is comprised of any bodily movement that may occur when doing active behaviors like organized sport, spontaneous play, or active transport, and can also be heavily impacted by sources of influence like school curricula, community infrastructure, and government policies. Maintaining high physical fitness in both health-related and skills-related fitness domains is a key tool for unlocking the habit of lifelong physical literacy, enabling young ones to better understand how their body works and fosters adaptation to movement challenges as they learn and grow.