Effects of Thermal Stress During Rest and Exercise in the Paediatric Population
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Thermoregulation during exposure to hot or cold environments differs between children and adults. Many physical and physiological changes occur during growth and maturation that can affect thermoregulation during rest as well as during exercise. Thus, physical as well as physiological differences between children and adults may explain the different response to thermal stress.
The main physical difference between children and adults affecting thermoregulation is the much higher surface—area-to-mass ratio of children. In a warm environment this allows them to rely more on dry heat loss and less on evaporative cooling. However, in extreme conditions, hot or cold, the greater surface—areato- mass ratio results in a higher rate of heat absorption or heat loss, respectively. The lower body fat in girls compared with women provides lower insulation and presents a disadvantage in a cold environment. The smaller blood volume in children compared with adults, even relative to body size, may limit the potential for heat transfer during heat exposure and may compromise exercise performance in the heat.
The main physiological difference between children and adults is in the sweating mechanism, affecting their thermoregulation in the heat, but not in the cold. The lower sweating rate characteristic of children is due to a lower sweating rate per gland and not to a lower number of sweat glands. In fact, children are characterised by a higher density of heat-activated sweat glands. The lower sweating rate per gland may be explained by the smaller sweat gland size, a lower sensitivity of the sweating mechanism to thermal stimuli and, possibly, a lower sweat gland metabolic capacity.
Other physiological differences between children and adults that may affect thermoregulation include metabolic, circulatory and hormonal disparities. The higher metabolic cost of locomotion in children provides an added strain on the thermoregulatory system during exercise in the heat. On the other hand, during acute exposure to cold it may prove advantageous by increasing heat production. Circulatory differences, such as a lower cardiac output at any given exercise intensity and the lower haemoglobin concentration in boys compared with men, are likely to increase the cardiovascular strain during exercise in the heat, although their effects in a cold environment are unknown. Finally, testosterone and prolactin are 2 hormones that differ in baseline levels between children and adults and may affect sweat gland function and sweat composition. These possible effects need to be further investigated.
The effectiveness of thermoregulation is reflected by the stability of core temperature. In a thermoneutral environment, children are characterised by a similar rectal temperature and a higher skin temperature when compared with adults. The latter may reflect the higher reliance on dry heat loss compared with evaporative cooling in children. In a hot environment, children’s body temperatures are higher compared with adults while walking and running but not necessarily while cycling. This may be related to the higher metabolic cost, and therefore higher heat production, in children while walking or running but not while cycling. In a cold environment, children are characterised by lower skin temperatures, reflecting greater vasoconstriction. Their metabolic heat is increased in the cold to a greater extent than that of adults, although this appears to be sufficient to maintain their body temperature during exercise but not during prolonged rest.
Neither children nor adults sufficiently replace fluid loss during exercise in the heat. Nevertheless, recent studies suggest that in children, when the available beverage is flavoured and enriched with NaCl and carbohydrates, dehydration can be prevented. The hypohydration, which frequently accompanies exercise in the heat, and the resultant added cardiovascular strain, may be more detrimental in children than in adults, because children rely more on dry heat loss, and therefore on elevated skin blood flow, to dissipate body heat.
Based on a few studies, it appears that acclimation to heat is similar in children and adults. The main difference is the slower rate of heat acclimation in children. No studies are available on cold acclimatisation or acclimation in children or adolescents.
Physical training results in enhanced thermoregulation during heat stress in children as in adults. Limited data suggest that training may improve thermoregulation during cold exposure in children. However, the effects of training on the thermoregulatory response to cold stress in children and adolescents need to be studied further.
KeywordsAdis International Limited Cold Stress Sweat Gland Cold Exposure Eccrine Sweat Gland
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- 4.Tochihara Y, Ohnaka T, Nagai Y. Thermal responses of 6- to 8-year old children during immersion of their legs in a hot water bath. Appl Hum Sci 1995; 14: 23–8Google Scholar
- 5.Forbes GB. Body composition in adolescence. In: Falkner F, Tanner JM, editors. Human growth: Vol. 2. 2nd ed. New York: Plenum Press, 1986: 119–45Google Scholar
- 7.Astrand PO. Experimental studies of physical work capacity in relation to sex and age. Copenhagen: Munksgaard, 1952Google Scholar
- 11.Bar-Or O. Pediatric sports medicine for the practitioner. New York: Springer Verlag, 1983: 259–99Google Scholar
- 15.Kawahata A. Sex differences in sweating. In: Yoshimura et al., editors. Essential problems in climatic physiology. Kyoto: Nankodo, 1960Google Scholar
- 17.Soldin SJ, Hicks JM. Pediatric reference ranges. Washington, DC: AACC Press, 1995Google Scholar
- 23.Bar-Or O. Temperature regulation during exercise in children and adolescents. In: Gisolfi CV, Lamb DR, editors. Perspectives in exercise science and sports medicine. Vol. 2: Youth, exercise and sport. Indianapolis: Benchmark Press, 1989: 335–62Google Scholar
- 25.Landing BH, Wells TR, Wiliamson ML. Studies on growth of eccrine sweat glands. In: Cheek DB, editor. Human growth: body composition, cell growth, energy and intelligence. Philadelphia: Lea & Febriger, 1968: 382–94Google Scholar
- 28.Kuno Y. Human perspiration. Springfield (IL): Charles C. Thomas, 1956Google Scholar
- 30.Szabo G. The number of eccrine sweat glands in human skin. Adv Biol Skin 1962; 3: 1–5Google Scholar
- 34.Araki T, Toda Y, Matsushita K, et al. Age differences in sweating during muscular exercise. Jpn J Fitness Sports Med 1979; 28: 239–48Google Scholar
- 35.Inbar O. Acclimatization to dry and hot environment in young adults and children 8-10 years old [dissertation]. Columbia University, 1978Google Scholar
- 40.Falk B, Bar-Or O. Longitudinal changes in peak aerobic and anaerobic mechanical power of circumpubertal boys. Pediatr Exerc Med 1993; 5: 318–31Google Scholar
- 41.Falk B. Physiological and health aspects of exercise in hot and cold climates. In: Bar-Or O, editor. Encylopaedia of sports medicine: the child and the adolescent athlete. Oxford: Blackwell Scientific, 1996: 326–52Google Scholar
- 42.Bittel J, Henane R. Comparison of neutral exchanges in men and women under neutral and hot conditions. J Physiol (Lond) 1975; 250: 475–489Google Scholar
- 44.McCormick RJ, Buskirk ER. Heat tolerance of exercising lean and obese middle-aged men [abstract]. Fed Proc 1974; 33: 441Google Scholar
- 47.Sohar E, Shapira Y. The physiological reactions of women and children marching during heat. Proc Isr Physiol Pharmacol Soc 1965; 1: 50Google Scholar
- 52.Araki T, Tsujita J, Matsushita K, et al. Thermoregulatory responses of prepubertal boys to heat and cold in relation to physical training. J Hum Ergol (Tokyo) 1980; 9: 69–80Google Scholar
- 56.Young A. Human adaptation to cold. In: Pandolf KB, Sawka MN, Gonzalez RR, editors. Human performance physiology and environmental medicine at terrestrial extremes. Indianapolis: Benchmark Press, 1988: 401–34Google Scholar
- 57.Carlson JS, Le Rossignol P. Children and adults exercising in hot wet climatic conditions with different levels of radiant heat [abstract]. North American Society of Pediatric Exercise Medicine, Ninth Annual Meeting; 1994 Aug 11-14; PittsburghGoogle Scholar
- 58.Marsh ML, Mahon AD, Naftzger LA. Children’s physiological responses to exercise in a cold and neutral temperature. Proceedings of the North American Society of Pediatric Exercise Medicine Meeting: 1992 Oct 30-Nov 1; MiamiGoogle Scholar
- 60.Mackie JM. Physiological responses of twin children to exercise under conditions of heat stress [MSc. thesis]. University of Waterloo, 1982Google Scholar
- 69.Shwachman H, Mahmoodian A. The sweat test and cystic fibrosis. Diagn Med 1982; Jun: 61–77Google Scholar
- 79.Meyer F, Bar-Or O, Salsberg A, et al. Hypohydration during exercise in children: effect on thirst, drink preferences, and rehydration. Int J Sports Nutr 1994; 4: 22–35Google Scholar
- 82.Bar-Or O, Inbar, O. Relationship between perceptual and physiological changes during heat acclimatization in 8- to 10-year-old boys. In: Lavalee H, Shephard RJ, editors. Frontiers of activity and child health. Québec: Pelican, 1977: 205–14Google Scholar
- 86.Matsushita K, Araki T. The effect of physical training on thermoregulatory responses of preadolescent boys to heat and cold. Jpn J Phys Fitness 1980; 29: 69–74Google Scholar