Tuesday, December 27, 2011

Are children more intolerant to exercise in the heat compared with adults?

The view that children are more intolerant to exercise in the heat than adults is based on early studies of Drinkwater et al (1977) and Wagner et al (1972). In the first study, young and adult females were asked to walk until exhaustion at various ambient conditions: 28oC and 45% relative humidity (rh), 35oC and 65% rh and 48oC and 10% rh. Their findings showed that more women completed the exercise task (2 times of 50min) compared with girls. Their conclusion was that young girls were more intolerant to exercise in the heat than women. However, in this study as well as in that of Wagner et al (1972) exercise intensity was not strictly controlled so that girls exercised at higher relative intensity than women and this could explain their relative inability to complete the exercise bouts in the heat.

What do recent studies show?
Recent studies suggest that no difference exists between children and adults in exercise tolerance in the heat when exercise is performed at similar relative intensity. For instance, Rowland et al (2008) asked 12 year old boys and 32 years old men to exercise at 65% of maximal oxygen uptake in the heat (31oC). Increases in core temperature, heart rate and cardiac index were similar in both groups. Exercise duration was also similar in the two age groups. Recently, Bergeron and colleagues (2009) showed that physiological stain (core temperature and heart rate) did not differ between 12-13 years old and 16-17 years old boys doing prolonged exercise in the heat (33oC).

Are children at increased risk for heat illness?
The traditional view is that children are at an increased risk for heat illness (heat stroke and heat exhaustion) compared with adults. This is based mainly on two observations: 1) thermoregulatory mechanisms of heat dissipation are lower in children, and 2) incidence of heat stroke is higher in the pediatric population during periods of heat waves. With regard to the first point, recent evidence shows that thermoregulatory responses do not differ between young boys and girls and adults when exercising at the same relative intensity. Regarding the latter point, there are indeed reports of elevated risk for heat stroke in infants and small children (<4 years old) primarily due to parental negligence.

In fact, there is very limited if any report in the literature of heat illness while children exercise in the heat.

  • Recent scientific evidence shows that there are NO differences in exercise tolerance and physiological strain between children and adults when exercising at the same relative intensity in the heat.
  • This challenges the traditional view of higher physiological stress and more intolerance to exercise in prepubertal boys and girls.
  • It seems that child athletes are not more susceptible to heat injuries than adults.

For more reading
-Bergeron et al. (2009). Repeated-bout exercise in the heat in young athletes: physiological strain and perceptual responses. Journal of Applied Physiology 106:476-485.
-Drinkwater et al. (1977). Response of prepubertal girls and college women to work in the heat. Journal of Applied Physiology 43:1046-1053.
-Rowland et al. (2008). Exercise tolerance and thermoregulatory responses during cycling in boys and men. Medicine & Science in Sports & Exercise 40:282-287.
-Wagner et al. (1972). Heat tolerance and acclimatization to work in the heat in relation to age. Journal of Applied Physiology 33:616-622.

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