Can Children Adapt to Temperature Changes More Efficiently Than Adults?
Nobody loves summer as much as kids do. Sure, adults like to sun-tan on the beach or go for a run on a Saturday morning, but kids, temporarily freed from school, truly run wild from June through August.
This is all well and good when it comes to playing around, but what about youth sports like a summer track series? Do children and adolescents have a harder time staying cool in the summer heat?
Heat regulation in kids and adolescents
When taking an initial look at the science, there are some good reasons to think that young athletes aren’t as heat-hardy as adults. Kids and teenagers don’t sweat as much as adults do, and their total blood volume is lower, even for their size.
Further, children are less efficient when it comes to using oxygen during weight-bearing exercise, meaning they require a higher effort level to maintain a given workload during exercise—say, eight-minute mile pace.
Although children and adolescents have a high ratio of skin surface area to body mass, which is usually an asset when it comes to heat loss, it can also mean that young athletes gain heat very quickly when the ambient temperature is higher than their body temperature.
These observations indicate that younger athletes would have a harder time exercising in the heat, and so for many years, guidelines called for more modest limits on exercise in hot weather for children.
For example, a 2000 policy statement by the American Academy of Pediatrics writes, “exercising children do not adapt to extremes of temperature as effectively as adults when exposed to a high climatic heat stress,” and a 1995 article in the Journal of Sports Sciences by Oded Bar-Or at McMaster University in Canada recommends curtailing training volume and workout intensity for children when the weather is hot.
Intensity vs. workload
As pointed out in a 2011 review article by Thomas Rowland, a pediatrician at Baystate Medical Center in Massachusetts, the initial studies which examined children’s ability to tolerate heat had some significant flaws.
Early research measured workloads in absolute terms—comparing heat production in children and adults while on a treadmill set to a certain speed, for example. But, Rowland points out that heat regulation is tied to relative intensity, not absolute workload.
He points to research like a 2004 study by Omri Inbar and other researchers in Australia and Israel that measured heat regulation in children, young adults, and elderly subjects during a cycling session in 105° F heat.
Critically, this study set exercise intensity as a constant percentage of the subject’s VO2 max. Contrary to previous studies, the researchers found that the children actually fared slightly better than the young adults when it came to regulating body temperature, even though they did indeed sweat less. Rowland himself, along with three coworkers at Baystate Medical Center, conducted a similar study in 2008, which found no differences in thermoregulation between eight boys and eight adult men during a cycling bout in 88° heat.
What of the differences in sweat rates?
Inbar et al. reconciled this by pointing out that the diminished sweat rate appears to be counterbalanced by the fact that the younger subjects weighed less, and hence had less body mass to cool, and by a higher sweating efficiency: sweat in children appears to coalesce into smaller, more diffuse droplets that can evaporate more rapidly.
This new wave of research caught the attention of the American Academy of Pediatrics, which released an updated policy statement in 2011 which included findings of newer studies. They, too, concluded that children and adolescents are just as tolerant of exercise in the heat as adults in similar circumstances.
The policy statement stresses that this only applies when relative effort levels are controlled for—children running at 60% of their VO2 max, for example, handle hot weather just as well as adults do at the same intensity, but it’s important to keep in mind that a given absolute workload (like running two miles in 15 minutes) is usually more stressful, and thus produces more heat, in a young runner since their overall fitness is typically lower.
Even though kids and teenagers aren’t any more susceptible to overheating during exercise than adults, it doesn’t mean they are immune either. Children and adolescents, just like the rest of us, need to know their limits during exercise in the heat.
Because of the basic physiology of exercise in hot weather, times and paces will be slower on a hot day. Keeping hydrated by drinking when thirsty and knowing when to dial back the day’s workload are common-sense precautions that make sense for everybody—not just for kids.