Behavioural thermoregulation: notes from a PhD thesis in temperature regulation (work in progress)

Although powerful, the functional capacity of human autonomic thermoregulation is however limited by physiological and biophysical constrains (Schlader et al. 2010). Maximal sweating as well as maximal vasodilation and vasoconstriction is limited by physiological (e.g. sweat gland density and output, number of capillaries) and biological factors (e.g. age) (Martini and Martini 1992; Kenney and Munce 2003). From a biophysical point of view, anthropometrical characteristic also play a role in limiting the functional ability of the autonomic thermoregulatory system. For example, body surface area to mass ratio is an important parameter for heat exchange, which can limit the ability to dissipate heat to the environment. Heat losses are indeed proportional to the gradient between skin and environment and to the surface area available for heat exchange (Havenith 2001b). Thus, given the same body mass, individuals with smaller body surface areas require greater increases in e.g. skin vasodilation and/or sweating than individuals with larger body surface areas in order to dissipate the same amount of heat to the environment, and to prevent core overheating.

Despite these intrinsic physiological limits, humans successfully maintain their thermal balance while being exposed to various extreme environments (e.g. from the moon surface to the Sahara desert), in which autonomic responses alone could not guarantee survival (Romanovsky 2007). In this respect, what assures survival to our specie is the virtually unlimited power of behavioural thermoregulation.

Behavioural thermoregulation can be defined as any conscious decision taken with the aim of maintaining thermal balance and it represents an infinite resource for human body temperature regulation (Schlader et al. 2010; Flouris 2011). Indeed, from simply looking for shade in a sunny and hot day (Parsons 2003), to adding or removing clothing (Havenith 2002), humans constantly adjust their thermal behaviour in order to maintain thermal comfort (Flouris 2011). 

Well, by the look of the fella in the photo we must have learned from our close relatives how to behaviourally thermoregulate :)

Davide Filingeri

PhD Researcher

Environmental Ergonomics Research Centre

Loughborough University, UK

In the picture: A shot from the Jigokudani Monkey Park (Nagano, Japan). The park is famous for its large population of wild Japanese Macaques (Macaca fuscata), more commonly referred to as Snow Monkeys, that go to the valley during the winter, foraging elsewhere in the national park during the warmer months. Starting in 1963, the monkeys descend from the steep cliffs and forest to sit in the warm waters of the onsen (hotsprings), and return to the security of the forests in the evenings (source: Wikipedia).

References

Flouris, A. D. (2011). Functional architecture of behavioural thermoregulation. European journal of applied physiology, 111(1), 1-8. doi:10.1007/s00421-010-1602-8

Havenith, G. (2001). Human surface to mass ratio and body core temperature in exercise heat stress—a concept revisited. Journal of Thermal Biology, 26, 387-393.

Havenith, G. (2002). Interaction of Clothing and Thermoregulation. Exogenous Dermatology, 1(5), 221-230. doi:10.1159/000068802

Kenney, W., & Munce, T. (2003). Invited review: aging and human temperature regulation. Journal of Applied Physiology, (18), 2598-2603.

Martini, F., & Martini, F. (1992). Fundamentals of anatomy and physiology.

Parsons, K. (2003). Human Thermal Environments. London, UK ET - Second: Taylor & Francis.

Romanovsky, A. (2007). Thermoregulation: some concepts have changed. Functional architecture of the thermoregulatory system. American Journal of Physiology- …, 85013, 64-66. doi:10.1152/ajpregu.00668.2006.

Schlader, Z., Stannard, S., & Mündel, T. (2010). Human thermoregulatory behavior during rest and exercise - a prospective review. Physiology & behavior, 99(3), 269-75. doi:10.1016/j.physbeh.2009.12.003