We are in the dog days of summer in eastern North Carolina, and it’s likely at this point you have chosen to forgo at least one outdoor activity due to high temperatures or humidity. Putting off activities until it “cools off” or getting up early to beat the heat may be part of your daily routine. Until you take the proper time to acclimate to the warmer weather, these are wise decisions. The good news is most individuals are fully capable of improving their body’s physiological responses to activity in the summer.

Throughout each day, our bodies utilize heat transfer mechanisms to maintain a core body temperature within a range of approximately 97.7 to 99.5 degrees. The mechanisms used to regulate our core temperature are radiation, convection, conduction and cooling through evaporation (perspiration). When we are active, our contracting muscles generate heat inside our body. This internal heat generation combined with high ambient temperatures result in an increasing core temperature. Upset by the rising core temperature, neural feedback sensors alert the hypothalamus in the brain to activate processes that result in widening of blood vessels (vasodilation) and sweat production. Simply put, increased blood flow to the skin and perspiration are the body’s way of releasing excess heat, as each drop of sweat that evaporates from the skin carries excess heat with it.

The problems with our efficient cooling process in high temperatures are the stress it places on our cardiovascular system and an enhanced risk of dehydration. As we sweat, our stroke volume, the amount of blood pumped by our heart with each beat, may decrease. Decreased stroke volume prompts an increase in our heart rate to provide sufficient blood flow to our muscles during activity. This “heart rate drift” can lead to decreases in performance and make outdoor activity in high temperatures feel more difficult for those untrained for hot environments. Humidity can further complicate our cooling process. When the water vapor pressure in the air is much lower than on our skin — from sweat — our evaporative cooling system works efficiently and our sweat readily vaporizes into the surrounding air. You might notice that on humid days you feel “sticky” because your sweat is not evaporating into the air quickly and stays on your skin much longer. Another issue to consider on hot, humid days is dehydration as a reduction in body fluids can lead to a decrease in rates of evaporation.

You may be thinking, “Why should I even attempt an activity outside in the heat?” Fortunately, our bodies are built to adapt to different environments; a necessity considering the variation in weather we experience here in eastern NC. During the first few days of activity in hot or humid environments, the American College of Sports Medicine (ACSM) recommends you engage in light intensity exercise and take frequent breaks. Subsequent outdoor activities in hot environments should gradually increase in intensity until you are capable of performing exercise to the duration and intensity you desire. If the acclimation process is carried out successfully, your body will better regulate core temperature by:

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Increasing sweat rates

Improving onset time of sweat

Increasing plasma volume

Decreasing heart rate at a specific workload

Increasing conservation of sodium

These benefits are sustained as long as exercise in the same environment is continued. Exposure to another environment or lack of continuous exercise in hot and humid elements can lead to a decrease in benefits of acclimation, and complete dissipation of benefits can occur after only two to three weeks. This means we are forced to re-acclimate annually to warmer weather after the winter months.

Even after acclimation occurs, we should exercise with caution during the summer months. Wearing clothing made of a loose, lightweight fabric that allows water vapor to freely pass through is recommended to avoid inhibiting our ability to sweat. You should still alter plans to avoid extremely hot conditions — temperatures over 90 degrees and relative humidity greater than 85 percent — by scheduling activities before 10 a.m. or after 6 p.m. Careful monitoring of fluid loss is also essential to reduce risk of dehydration. One way of monitoring fluid loss is to weigh yourself before exercising outdoors. Once you are finished with your activity, replenish the weight lost during exercise and be careful to restore electrolyte levels as well. Refrain from consuming caffeine and alcohol before exercising outdoors and avoid waiting until you are thirsty to replenish fluids; drink 5–10 ounces per 15 minutes of activity in the heat. Exercising in our hot and humid environment may present certain challenges, but with the proper strategies in place, safe and healthy exercise is possible.

Travis Rogerson, BS, is an exercise specialist and can be reached at Vidant Wellness Center, Washington, 252-975-4236.