# Cooling and pre-cooling during exercise under heat stress: insights into the debate "Skin vs. Core temperature"

From: http://environmental-exercise-physiology.blogspot.co.uk/

Human temperature regulation is challenged during exercise in the heat (Cheuvront et al. 2010). The increase in the metabolic heat production (resulting from exercising muscles), and the decrease in the gradient for heat loss to the environment (resulting from high ambient temperatures and humidity), translate into an increased rate of body heat storage (Tikuisis, McLellan, & Selkirk, 2002; Gleeson, 1998). This results into a quicker obtainment of the “critical” (~40°C) core temperature (Tc) (Cheung & Sleivert 2004), suggested as the main limit to aerobic performance in the heat (González-Alonso & Teller 1999). Elevated Tc can result in a decreased neural drive to contraction (Nybo & Nielsen 2001), as well as in cellular perturbations, which could disrupt metabolic and contractile processes within skeletal muscle (Febbraio 2000).

Pre-cooling strategies (i.e. cold water immersion, cooling garments, ice/fluids ingestion) have been developed to counterbalance the effects of exercising under heat stress (Wegmann et al. 2012; Siegel 2012; Quod et al. 2006). These methods have primary focused on reducing Tc before exercise, in order to increase the margin for metabolic heat production, and thus the time to reach the critical temperature (F. Marino 2002).

However, emerging evidence suggests that the role of hot (>35°C) skin temperature  (Tsk) is also critical in impairing aerobic performance under heat stress (Kenefick et al. 2010; Sawka et al. 2012; Cheuvront et al. 2010). Elevated Tsk narrows the skin to core temperature gradient, thus increasing the skin blood flow requirements, and eventually resulting in an increased level of cardio-vascular strain (Sawka et al. 2012). This is exacerbated by the competition for the available cardiac output between the blood flow required by the exercising muscles to meet the oxygen demands, and the blood flow required by the skin to meet the demands of temperature regulation (i.e. heat dissipation to the environment) (González-Alonso et al. 2008). Also, heat-induced changes in Tsk influence perceptual and cutaneous-sensory feedbacks such as thermal sensation, comfort and “sensation of fatigue”, (Cheung 2010; Noakes 2012), which have been proposed as critical determinants of pacing strategies during performance under heat stress (Tucker & Noakes 2009; Marcora et al. 2009)

Therefore, in order to preserve performance under heat stress, keeping the skin cool during the exercise, might be as important as a pre-exercise reduction in Tc (Schlader et al. 2011).

Cooling methods, such as air and water cooled systems (Stephenson et al. 2007; Cadarette et al. 2006; Cadarette et al. 2002), garments made of phase change materials (House et al. 2013; Bergmann Tiest et al. 2012), as well as the use of menthol (Gillis et al. 2010; Lee et al. 2012), have been developed and shown to be potentially effective in preserving performance in the heat, due to their effects on skin and whole body temperature (Smolander & Dugue 2012; Hasegawa & Takatori 2005; Lopez et al. 2008). However, due to some specific disadvantages, such as weight of the systems, wearability of the garments or side effects of menthol application (i.e. skin irritation), these methods still present numerous practical limitations (Marino 2002; Quod et al. 2006).

In this respect, evaporative cooling garments (e.g. Personal Cooling System, Unico, Switzerland; Omni Freeze-Zero, Columbia USA; KoolSorb, Technical Absorbent, UK) have recently received attention, as they could represent a potentially effective alternative to more traditional cooling methods (Bogerd et al. 2010; Webster et al. 2005; Sakoi 2011; Kocjan & Rothmaier 2007). These light weight garments induce mild-cooling via the process of water evaporation. These are made of particular hydrophilic fabrics, which, if wetted, allow improved water evaporation, thereby cooling the shirt and underlying skin.

However, although using the concept of evaporative cooling translates into the possibility to design cooling garments which are light weight and practical, the limited empirical evidence on their physiological as well as perceptual (i.e. thermal comfort) effects, made any conclusion on these methods difficult to drawn. Nevertheless, there is a clear need to develop cooling systems which would result effective in counteracting the thermal strain, as well as practical and thermally comfortable  (Flouris & Cheung 2006; Cadarette et al. 2006; Minniti et al. 2011; Marino 2002).

This has important practical applications, not only for elite performance under heat stress (Cheung 2010), but also, in the context of amateur and recreational exercise. Indeed, individuals who enjoy outdoor sporting activities, such as running or cycling, encounter a variety of environmental conditions, some of which (e.g. heat) can significantly decrease their thermal comfort (Vanos et al. 2010; Brotherhood 2008). As the type and amount of physical activity performed has been shown to be influenced by the level of comfort achievable with the surrounding environment (Vanos et al. 2012), developing a practical cooling method, able to reduce the thermal discomfort experienced while exercising in the heat, might have a positive impact on the activity levels of healthy individuals.

Davide Filingeri
PhD Reseracher
Environemntal Ergonomics Research Centre

References

Bergmann Tiest, W. M., Kosters, N. D., Kappers, A. M. L., & Daanen, H. a M. (2012). Phase change materials and the perception of wetness. Ergonomics55(4), 508-12. doi:10.1080/00140139.2011.645886
Bogerd, N., Perret, C., Bogerd, C. P., Rossi, R. M., & Daanen, H. a M. (2010). The effect of pre-cooling intensity on cooling efficiency and exercise performance. Journal of sports sciences28(7), 771-9. doi:10.1080/02640411003716942
Brotherhood, J. (2008). Heat stress and strain in exercise and sport. Journal of science and medicine in sport / Sports Medicine Australia11(1), 6-19. doi:10.1016/j.jsams.2007.08.017
Cadarette, B., Cheuvront, S., Kolka, M., Stephenson, L., Montain, S., & Sawka, M. (2006). Intermittent microclimate cooling during exercise-heat stress in US army chemical protective clothing. Ergonomics49(2), 209-19. doi:10.1080/00140130500436106
Cadarette, B., Levine, L., Kolka, M., Proulx, G., Correa, M., & Sawka, M. (2002). Heat strain reduction by ice-based and vapor compression liquid cooling systems with a toxic agent protective uniform. Aviation, Space and Environmental Medicine73(7), 665–672. Retrieved from http://nsrdec.natick.army.mil/LIBRARY/00-09/R02-21.pdf
Cheung, S. S. (2010). Interconnections between thermal perception and exercise capacity in the heat. Scandinavian journal of medicine & science in sports20 Suppl 3, 53-9. doi:10.1111/j.1600-0838.2010.01209.x
Cheung, S. S., & Sleivert, G. G. (2004). Multiple triggers for hyperthermic fatigue and exhaustion. Exercise and sport sciences reviews32(3), 100-6. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/15243205
Cheuvront, S. N., Kenefick, R. W., Montain, S. J., & Sawka, M. N. (2010). Mechanisms of aerobic performance impairment with heat stress and dehydration. Journal of applied physiology (Bethesda, Md. : 1985)109(6), 1989-95. doi:10.1152/japplphysiol.00367.2010
Febbraio, M. (2000). Does muscle function and metabolism affect exercise performance in the heat? Exercise and sport sciences reviews. Retrieved from http://journals.lww.com/acsm-essr/Abstract/2000/28040/Does_Muscle_Function_and_Metabolism_Affect.6.aspx
Flouris, A., & Cheung, S. (2006). Design and control optimization of microclimate liquid cooling systems underneath protective clothing. Annals of biomedical engineering34(3), 359–372. Springer. doi:10.1007/s10439-005-9061-9
Gillis, D. J., House, J. R., & Tipton, M. J. (2010). The influence of menthol on thermoregulation and perception during exercise in warm, humid conditions. European journal of applied physiology110(3), 609-18. doi:10.1007/s00421-010-1533-4
González-Alonso, J, & Teller, C. (1999). Influence of body temperature on the development of fatigue during prolonged exercise in the heat. Journal of Applied …, 1032-1039. Retrieved from http://www.jappl.org/content/86/3/1032.short
González-Alonso, José, Crandall, C. G., & Johnson, J. M. (2008). The cardiovascular challenge of exercising in the heat. The Journal of physiology586(1), 45-53. doi:10.1113/jphysiol.2007.142158
Hasegawa, H., & Takatori, T. (2005). Wearing A Cooling Jacket During Exercise Reduces Thermal Strain and Improvesendurance Exercise Performance in A Warm Environment. The Journal of Strength …19(1), 122-128. Retrieved from http://journals.lww.com/nsca-jscr/Abstract/2005/02000/Wearing_A_Cooling_Jacket_During_Exercise_Reduces.21.aspx
House, J. R., Lunt, H. C., Taylor, R., Milligan, G., Lyons, J. a, & House, C. M. (2013). The impact of a phase-change cooling vest on heat strain and the effect of different cooling pack melting temperatures. European journal of applied physiology113(5), 1223-31. doi:10.1007/s00421-012-2534-2
Kenefick, R. W., Cheuvront, S. N., Palombo, L. J., Ely, B. R., & Sawka, M. N. (2010). Skin temperature modifies the impact of hypohydration on aerobic performance. Journal of applied physiology (Bethesda, Md. : 1985)109(1), 79-86. doi:10.1152/japplphysiol.00135.2010
Kocjan, N., & Rothmaier, M. (2007). A new cooling garment for patients with multiple sclerosis. In I. B. Mekjavic, S. N. Kounalakis, & N. A. S. Taylor (Eds.), International Conference on Environmental Ergonomics (pp. 395-398).
Lee, J.-Y., Nakao, K., Bakri, I., & Tochihara, Y. (2012). Body regional influences of L-menthol application on the alleviation of heat strain while wearing firefighter’s protective clothing. European journal of applied physiology112(6), 2171-83. doi:10.1007/s00421-011-2192-9
Lopez, R., Cleary, M., Jones, L., & Zuri, R. (2008). Thermoregulatory influence of a cooling vest on hyperthermic athletes. Journal of athletic training43(1), 55-61. doi:10.4085/1062-6050-43.1.55
Marcora, S. M., Staiano, W., & Manning, V. (2009). Mental fatigue impairs physical performance in humans. Journal of applied physiology (Bethesda, Md. : 1985)106(3), 857-64. doi:10.1152/japplphysiol.91324.2008
Marino, F. (2002). Methods, advantages, and limitations of body cooling for exercise performance. British journal of sports medicine36(2), 89-94. Retrieved from http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1724476&tool=pmcentrez&rendertype=abstract
Minniti, A., Tyler, C., & Sunderland, C. (2011). Effects of a cooling collar on affect, ratings of perceived exertion, and running performance in the heat. European journal of sport science11(6), 419-429. Taylor & Francis. Retrieved from http://www.tandfonline.com/doi/abs/10.1080/17461391.2010.536577
Noakes, T. D. (2012). Fatigue is a Brain-Derived Emotion that Regulates the Exercise Behavior to Ensure the Protection of Whole Body Homeostasis. Frontiers in physiology3(April), 82. doi:10.3389/fphys.2012.00082
Nybo, L., & Nielsen, B. (2001). Hyperthermia and central fatigue during prolonged exercise in humans. Journal of Applied Physiology, 1055-1060. Retrieved from http://jap.physiology.org/content/91/3/1055.short
Quod, M., Martin, D., & Laursen, P. (2006). Cooling athletes before competition in the heat: comparison of techniques and practical considerations. Sports medicine (Auckland, N.Z.)36(8), 671-82. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/16869709
Sakoi, T. (2011). Use of clothing for body cooling by evaporation. Indoor air.
Sawka, M. N., Cheuvront, S. N., & Kenefick, R. W. (2012). High skin temperature and hypohydration impair aerobic performance. Experimental physiology97(3), 327-32. doi:10.1113/expphysiol.2011.061002
Schlader, Z. J., Simmons, S. E., Stannard, S. R., & Mündel, T. (2011). Skin temperature as a thermal controller of exercise intensity. European journal of applied physiology111(8), 1631-9. doi:10.1007/s00421-010-1791-1
Siegel, R. (2012). Keeping Your Cool: Possible Mechanisms for Enhanced Exercise Performance in the Heat with Internal Cooling Methods. Sports Medicine42(2), 89-98. Retrieved from http://www.ingentaconnect.com/content/adis/smd/2012/00000042/00000002/art00001
Smolander, J., & Dugue, B. (2012). Adding a cooling vest during cycling improves performance in warm and humid conditions. Journal of Thermal Biology37, 47-55. doi:10.1016/j.jtherbio.2011.10.009
Stephenson, L., Vernieuw, C., Leammukda, W., & Kolka, M. (2007). Skin temperature feedback optimizes microclimate cooling. Aviation, space, and environmental medicine78(4), 377–382. Aerospace Medical Association. Retrieved from http://www.ingentaconnect.com/content/asma/asem/2007/00000078/00000004/art00004
Tikuisis, P., McLellan, T. M., & Selkirk, G. (2002). Perceptual versus physiological heat strain during exercise-heat stress. Medicine and science in sports and exercise34(9), 1454-61. doi:10.1249/01.mss.0000027764.43430.fe
Tucker, R., & Noakes, T. D. (2009). The physiological regulation of pacing strategy during exercise: a critical review. British journal of sports medicine43(6), e1. doi:10.1136/bjsm.2009.057562
Vanos, J., Warland, J., Gillespie, T., & Kenny, N. (2010). Review of the physiology of human thermal comfort while exercising in urban landscapes and implications for bioclimatic design. International journal of biometeorology54(4), 319–334. Springer. Retrieved from http://www.springerlink.com/index/Y015581772853724.pdf
Vanos, J., Warland, J., Gillespie, T., & Kenny, N. (2012). Thermal comfort modelling of body temperature and psychological variations of a human exercising in an outdoor environment. International journal of biometeorology56(1), 21-32. doi:10.1007/s00484-010-0393-2
Webster, J., Holland, E. J., Sleivert, G., Laing, R. M., & Niven, B. E. (2005). A light-weight cooling vest enhances performance of athletes in the heat. Ergonomics48(7), 821-37. doi:10.1080/00140130500122276
Wegmann, M., Faude, O., & Poppendieck, W. (2012). Pre-Cooling and Sports Performance: A Meta-Analytical Review. Sports42(7), 545-564. Retrieved from http://www.ingentaconnect.com/content/adis/smd/2012/00000042/00000007/art00001