Heat Acclimation: The Body’s Remarkable Ability to Adapt to Changing Environments

Persons who enjoy exercising out of doors inevitably encounter inclement weather. Yet given time to acclimate, the body adjusts remarkably well to extremes of heat and cold. While exercising at cooler times of the day, wearing the proper apparel and paying attention to hydration are important safety considerations in the summer, it is equally crucial to give the body ample time to acclimate, about 14 days for most individuals.

Early in the process, you may find yourself changing certain behaviors to adjust for the warmer temperatures, such as seeking shade whenever possible, and making sure you have enough water on hand. A hat to keep the sun off the face helps, as does avoiding peak sun hours (10 am- 3 pm). Your exercise intensity may dip slightly as well during this period of adjustment.

At the same time, the body automatically undergoes a remarkable physiologic transformation, to maintain what is known as a ‘set point’ (Periard et al., 2014). The set point is the body’s ideal core temperature, which is about 37 degrees Celsius or 98.6 degrees Fahrenheit. The adaptations occur both in the perimeter (changes in sweating and skin blood flow) and more centrally (increased fluid retention for greater plasma volume).

Once acclimated, you will begin to sweat earlier and more profusely, to help cool down your skin. The composition of sweat also changes with acclimation, with a lower concentration of sodium. This enables the body to conserve a very important electrolyte, and also causes the sweat the evaporate off of the skin faster, for more efficient cooling. While you may find your heart rate increases at the beginning of the hot weather, it will gradually decrease as the body becomes more efficient at dispersing heat. Changes in certain hormone levels account for increases in total body water, to ensure adequate hydration (Periard et al., 2014). Once acclimated, athletes are typically better able to match their thirst to hydration needs, given adequate water (Periard et al., 2014).

The body will only maintain these changes as long as the individual continues to exercise in warm temperatures. Escaping the hot weather for a month mid-summer may mean starting the process over again once your return home. Generally, the body will maintain acclimation for about 2 weeks following the last heat exposure (Periard et al., 2014). The amount of time adaptation continues depends somewhat on how long the person has exercised in the heat prior to leaving, how intensely and how long he or she has exercised in the heat, and general fitness.

When exercising in the heat, understand the symptoms of heat exhaustion and heat stroke, and know what to do. Heat exhaustion is marked by headache, dizziness, nausea and excessive sweating. It is imperative to get out of the heat and seek shade and fluids immediately (CDC.gov, n.d.). The progression from heat exhaustion to heat stroke, which is a medical emergency, can be rapid. Symptoms of heat stroke are hot, dry skin, confusion and in some cases, loss of consciousness. Heat stroke can be fatal if not properly treated. If you notice someone experiencing heat stroke, call 911 immediately. While waiting for assistance, do whatever is possible to cool the body down by covering the skin with ice bags if available, a cool wet towel, and soaking the clothing in cool water. For more information on heat stress, visit the CDC website.

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