Working Out in the Heat (Summer Training Benefits and Safety)As impressive as your adaptive responses are—these responses handle small acute adaptations to heat with aplomb—sudden and significant changes in your environment can overwhelm them. As with many homeostatic responses, your body has acute responses and chronic responses. Chronic responses to changes in heat take place over about two weeks of increasing temperatures. This kind of adaptive homeostasis works well in preparing you for high summer training but is different from exposure to harmful heat. The physiological equivalent of "that which does not kill us, makes us stronger," it is not something you want to test out with heat stress.
Working Out in the Heat (Safety and Benefits)
Summer is great for training. Motivation is high with all the graduations, weddings, and vacations. Plus, more leisure usually means more training time. Often the only problem is the heat. Even if you train in an airconditioned space, spending time outdoors in the summer heat is draining. Garage gyms or basement gyms can feel anywhere from uncomfortable to dangerous. Fortunately, our muscles don’t melt in the heat, and our bodies are pretty good at handling changes in climate. There are some risks to training in the heat, but there are also some benefits. If you know what to look for and how to manage the potential problems, you can keep your training safe and productive through the hot summer months.
Adapt, Don’t Avoid
Instinct often moves us to avoid the heat; this isn’t your best summer strategy. The most potential problems come from sudden changes in your environment—such as sudden heat waves or traveling from a cool, dry climate to a hot, tropical one. Otherwise, the seasonal onset of summer heat, however, is an excellent time to acclimate.
Our bodies have an impressive ability to adapt to the heat. Just like you adapt to training stress by getting stronger, you can adapt to heat stress as well with various protective mechanisms. We have two main protective mechanisms for heat adaptation: (1) behavioral changes (things we do consciously or instinctively in response to heat) and (2) automatic changes (internal alternations controlled by your central nervous system trying to maintain homeostasis).
Behavior changes are obvious. Most people experiencing heat stress wear less clothing, drink more water, and cool themselves. Watch how people waiting in a line at the amusement park clump around the always-insufficient patches of shade. Behavioral changes are similar to a hunger or thirst response; your body tells you it needs something and your natural response is to provide it.
Automatic physiological responses to heat are all about heat dissipation through sweat and circulation. Vasodilation, the widening of your superficial blood vessels, increases blood flow from your body’s core to its surface near your skin. Sweat evaporation transfers heat away from your body, so you sweat more to keep cool. Adaptations to chronic heat stress revolve around this evaporative cooling—maintaining your fluid balance so that you can sweat freely and improving your body’s ability to transfer heat from your core to your skin, where it can be carried off through evaporation.
These responses are the same whether you are in a dry or humid climate. Though different climates offer different challenges to staying cool. In dry climates, rapid sweat evaporation carries the potential to burn through your body’s water supply more quickly, increasing the risk of dehydration, which is one of two conditions for heat exhaustion. In dry climates, you should take a more intentional approach to maintain your fluid balance. Humidity, on the other hand, keeps sweat from evaporating, undermining your built-in cooling system. You still sweat, but it does not cool you down as effectively. In dry climates, adding moisture to the air or your skin directly can help with your evaporative cooling. In humidity, convection methods like a big cooling fan can make a difference by helping sweat evaporate from your skin.
As impressive as your adaptive responses are—these responses handle small acute adaptations to heat with aplomb—sudden and significant changes in your environment can overwhelm them. As with many homeostatic responses, your body has acute responses and chronic responses. Chronic responses to changes in heat take place over about two weeks of increasing temperatures. This kind of adaptive homeostasis works well in preparing you for high summer training but is different from exposure to harmful heat. The physiological equivalent of “that which does not kill us, makes us stronger,” it is not something you want to test out with heat stress.
When exercising in the heat, you run the risk of heat exhaustion, which, if ignored, can progress to heat stroke. Both are illnesses related to the more general classification of hyperthermia. Hyperthermia occurs from “a rise in body temperature above the hypothalamic set point when heat-dissipating mechanisms are impaired (by drugs or disease) or overwhelmed by external (environmental or induced) or internal (metabolic) heat.” (Bouchama A, Knochel JP, “Heat Stroke,” N Engl J Med 346: 1978-1988 (2002).) Hyperthermia is an unexpected increase in body temperature that may indicate a severe condition, depending on the underlying cause, as in the case of exertional heat stroke.
Heat exhaustion (HEX) is a mild-to-moderate illness that comes from two conditions—a high ambient temperature and some form of dehydration—and causes cardiovascular strain. There are two forms of heat exhaustion, characterized by the nature of dehydration that accompanies them. Water-depletion HEX comes from insufficient fluid intake when the concentration of salts in your plasma increases relative to the amount of water. This form of HEX is an acute form due to exercise in the heat combined with inadequate hydration. It is the more common form of heat exhaustion. Salt-depletion HEX occurs from an inadequate replacement of salt losses from sweat and urine. Salt depletion is a chronic condition that requires a longer-term, nutrition-based solution. (Armstrong, Lopez, “Return to Exercise Training After Heat Exhaustion,” J. of Sports Rehab., 16, pp. 182-89 (2007).) Both forms of HEX are marked by the insufficiency of the body to meet its cooling demands and tend to lead to cardiac strain and a reduction in exercise performance.
Though heat exhaustion is not considered life-threatening, it’s essential to recognize the signs and take action. Signs include intense thirst, weakness, discomfort, anxiety, dizziness, fainting, and headache. At the first signs of exertional HEX, a person should seek out a cool, shaded place or indoor, air-conditioned building. If severe, remove excess clothing and elevate the person’s legs to improve circulation for cooling and reduce cardiovascular strain. Unless there is vomiting, the person should drink chilled fluids to restore fluid balance. Severe heat exhaustion may also include a loss of consciousness or an “altered mental status.” You can usually prevent severe heat exhaustion by stopping your activity, cooing off, and hydrating. When HEX becomes severe, however, it may be impossible to distinguish heat exhaustion (HEX) from the medical emergency heat stroke.
Exertional heat stroke is a severe condition in which the person’s core temperature exceeds 40°C and is accompanied by confusion, delirium, convulsions, or unconsciousness. In a hospital, HEX can be distinguished from heat stroke by a core temperature below 40°C, consciousness, and normal serum enzyme levels. Outside of a hospital setting, if a person “exhibits symptoms of both severe HEX and exertional heat stroke, whole-body cooling should be instituted immediately after hyperthermia is discovered or if rectal temperature cannot be measured promptly. Cold or ice water immersion provides the most rapid cooling rate and the most effective therapy for hyperthermia.” If you suspect someone may be suffering from severe HEX or heat stroke, get medical attention.
Recovering from Heat Exhaustion
Now, say you spent part of your weekend hiking. During the hike, it was hot, and you pushed yourself pretty hard. You think you were starting to experience heat exhaustion, but you got yourself to a cool place, kept hydrated, and finished your day without incident. You likely felt tired, both from the heat and from the hike. But is the brush with HEX enough to derail your training for the week? Did the heat compromise your recovery ability enough that you need to change your planned programming?
If you experience heat exhaustion, you need to take the rest of the day off, and you may need a reduction in overall training stress for a few days. “Neither rest nor body cooling allows heat exhaustion patients to recover to full exercise capacity on the same day.” (Armstrong and Lopez). There are some best practices to prevent more extended layoffs due to heat exhaustion.
- Train consistently. People with higher levels of fitness tend to return to regular training more quickly and experience fewer complications due to heat exhaustion.
- Drink water. The more quickly you restore your fluid balance, the more quickly you recover from untoward heat stress.
- Cool down. Those who experience HEX tend to have better outcomes when cooled off quickly following the onset of symptoms.
“The most significant reduction of risks involves seeking to improve fitness and heat acclimatization status.” (Armstrong and Lopez)
Benefits of Training in the Heat
Training in the heat is not inherently a bad thing. Many possible adaptive benefits come from training in a hot environment. Acclimatization to training in the heat tends to improve your overall capacity for acute adaptive responses to hot climates, you sweat more easily, have increased blood volume, and you improve your ability to continue exercising in hot environments without affecting your ability to exercise in the cold.
In the same way that endurance athletes train at high altitudes for the ancillary benefits of high-altitude acclimatization, training in the heat carries additional benefits as well. While you should know if you are predisposed to heat exhaustion due to poor fitness, dehydration, or lacking acclimatization to extreme heat, you should also embrace the heat this summer. Keep safe, but keep training—and drink your water.