Skin vs. Core temperature: Recent insights on human thermoregulation

Few intense week of data collection have kept me away from writing new posts on this blog.
As I am slowly coming back to "life", I have thought it would have been nice to keep the reader of this blog busy with some interesting and very recent papers.
The one I am presenting today, edited by Zachary J. Schlader and published on the latest issue of the EJAP, explores the topic of the human temperature regulation when given the opportunity to behave.
Interestingly, the findings of this paper indicate skin more than core temperature, to play a signalling role in the decision to behaviourally thermoregulate. I say interestingly because, the debate about "skin vs. core temperature" in influencing human thermoregulation and behaviours is currently a hot topic, especially when looking at endurance performance under heat stress.
For many years indeed, core temperature and its rate of increase, has been identified  as the main factor limiting performance during exposure to heat (Marino, 2002).
However, Micheal N. Sawka, has recently pointed out that no study has demonstrated that high core temperature (∼40◦C) alone, without coexisting hot skin,will impair aerobic performance (Sawka et al., 2012). Conversely, aerobic performance is sustained with core temperatures >40◦C if skin temperatures are cool-warm when euhydrated (Sawka et al., 2012).
Although in Schlader' study participants were not exercising, those outcomes seem in line with the hypothesis of the greater role of skin rather than core temperature in influencing human thermoregulation and thus performance.

So then again, a topic everyone is more than welcome to contribute to with their personal thoughts or research experiences.

Enjoy it!

HUMAN TEMPERATURE REGULATION WHEN GIVEN THE OPPORTUNITY TO BEHAVE

Schlader ZJ, Perry BG, Jusoh MR, Hodges LD, Stannard SR, Mündel T.

Eur J Appl Physiol. 2012 Nov 23. [Epub ahead of print]

ABSTRACT

This study aimed to test the primary hypotheses that human thermoregulatory behavior is: (1) initiated before changes in rectal or esophageal temperatures; and (2) accompanied by indiscernible differences in sweating or shivering. This was achieved by placing nine, healthy, males in a situation where they were free to move between a cold (~8 °C) and a hot (~46 °C) environment. Upon behaving [i.e., move from cold to hot (C→H) or from hot to cold (H→C)], skin, rectal, and esophageal temperatures, indices of cutaneous vasomotor tone, metabolism and evaporation, and local and whole-body thermal discomfort were recorded. Rectal temperatures were similar at H→C (37.1 ± 0.2 °C) and C→H (37.1 ± 0.2 °C); yet esophageal temperatures were higher at C→H (36.9 ± 0.2 vs. 36.8 ± 0.2 °C). Skin temperature (C→H, 28.4 ± 0.9 vs. H→C, 35.0 ± 0.6 °C) and vasomotor tone were drastically different upon the decision to behave. Metabolic heat production was lower at H→C (79 ± 10 W/m²) than at C→H (101 ± 20 W/m²), yet there were no statistical differences in evaporative heat loss (C→H, 23 ± 33 W/m² vs. H→C, 52 ± 36 W/m²). Whole-body thermal discomfort was similar at C→H and H→C, yet there were inter-segmental differences. These findings indicate that skin temperature, not core temperature, plays a signaling role in the decision to behaviorally thermoregulate. However, this behavior does not occur in the complete absence of autonomic thermoregulatory responses.

http://link.springer.com/article/10.1007%2Fs00421-012-2544-0?LI=true 


References

Marino, F. (2002). Methods, advantages, and limitations of body cooling for exercise performance. British journal of sports medicine, 36(2), 89-94

Sawka, M. N., Cheuvront, S. N., & Kenefick, R. W. (2012). High skin temperature and hypohydration impair aerobic performance. Experimental physiology, 97(3), 327-32