It’s been a hot summer. And that may be the understatement of the year. When the temperature consistently hits these highs, it becomes difficult to stick to workout routines or even get outside for a walk. But, could there be benefits to getting outside and embracing the heat?
Getting outside in the heat can be viewed as a form of physiological stress. The beneficial health effects associated with many therapeutic strategies are explained by their ability to induce a small stress. This concept is known as hormesis and describes the idea whereby a low amount of stress promotes a positive adaptation and improved health, whereas a high dose can have toxic effects. This idea was famously distilled by the a 15th century physician Paracelsus when he stated “it’s the dose that makes the poison.” More recently, in the late 19th century, the German philosopher Friedrich Nietzsche touched on this idea when he coined the phrase “…what does not kill me makes me stronger.” Thus, a little bit of heat can be good, too much of it is bad.
Upon heat stress, heart rate increases in order to divert blood to the skin and increase heat dissipation. One of the best predictors of mortality (risk of dying) is how many times an individual’s heart rate is elevated over the course of their lifetime (typically in response to exercise). If an individual engages in aerobic activity and their heart rate is increased, they live longer. Therefore, a minor amount of heat stress and the corresponding elevation in heart rate could be beneficial over the long term.
How about exercise training in the heat? If I was to train in hot conditions, would I be stronger because of the added stress? A study out of the University of Oregon answered this question when they trained cyclists under heat stress (10 days of training at 40ºC), and found that after heat training, their exercise performance improved in hot AND cool conditions. The heat training improved the athlete’s ability to dissipate heat which led to improved exercise performance. Exercising in the heat will also make exercising in the cool feel magnificent. You never know how good something is until you’re deprived of it. However, it is important to note that dehydration and heat stroke can happen rapidly, especially when exercising. These are serious conditions and deserve the utmost respect. If you are heading out into the heat, consider your hydration plan, a hat and sunscreen.
Also consider that if you are out in the heat walking your dog, your ability to thermoregulate is remarkably superior vs. Fido. Human beings are one of the most well-equipped animals to tolerate heat stress. We are not covered in hair and our largest organ is our heat-dissipating skin. Within the skin the average person has 2.6 million sweat glands including a thermoregulatory-specific type known as “eccrine glands.” No other animal compares.
From an evolutionary perspective, the fact that we are good at sweating may have played an integral role in vaulting us to the top of the food chain. It was about 2.5 million years ago when our ancestors began to consume larger quantities of meat. To obtain meat, a hunting practice known as persistence hunting was employed. Early humans would track large mammals across the African savannah for many days. The advantage humans had was that they were able to tolerate the heat stress of running for days under a scorching sun. In contrast, the large mammal they were hunting would become overheated and fall under the spell of heat stroke. Animal meat is calorically dense and high in protein, two ingredients required for increased brain development. Higher brain development and subsequent creativity and intelligence is arguably our species greatest asset. Therefore, because we are good at sweating, we were able to capture a calorie-dense food source which allowed us to develop complicated neuronal circuits, thereby contributing to the evolutionary success of our species. Or, another way to look at it; it is because of the heat that our species is successful as it was the heat that provided us the opportunity to use our thermoregulatory advantage.
So remember that if something feels physically difficult – you are likely in a health-improving situation. Training in the heat could improve performance on game day, and we may even have heat to thank for our evolutionary success. Let’s all grab a water bottle, a hat and sunscreen and embrace the heat.
By Brennan Smith, PhD
