Bring on the Heat with Summertime Exercise Imagine what it feels like to step outside on a hot and humid day, with the air heavy and sticky on your skin. Now imagine lacing up your tennis shoes and going for a run on that hot and humid day. What does it feel like? And how does the warm outdoor temperature affect your body and overall physical performance? The temperature of your exercise environment can elevate your heart rate and make it more difficult to breathe—possibly having a negative impact on your exercise ability. Humans are “homeotherms,” meaning that our body temperature is regulated to remain close to a set point of 98.6°F or 37°C. Our bodies constantly try to maintain control over our core temperature, keeping it close to its set point in order to avoid potentially life threatening situations like heat stroke, exhaustion, fatigue, or dehydration. When exercising in a warmer climate, your body naturally produces heat and takes heat from the external environment and transfers it to your body1. To safely exercise in the heat, it is important to adapt your body and maintain hydration. To adapt your body, expose yourself to hot and humid environments regularly to allow your body’s sweat response to catch up with the rest of your body’s systems. To avoid over-exerting yourself when exercising in the heat, gradually increase activity intensity and duration. When you are at rest, or not exercising, your body normally balances hydration by initiating a thirst response that informs your brain and body to drink fluids. During exercise however, this thirst response may not be sufficient. A fluid loss of 1-2% of body weight is necessary before your body will initiate a thirst response, therefore making it necessary to understand and respond to your fluid needs2,3. Begin a workout fully hydrated. In fact, before exercise, hydrate slightly more than normal to optimize your body’s ability to control its temperature and maintain cardiac output, or the rate of blood pumping from the heart. According to the American College of Sports Medicine, you should drink 500 milliliters of fluid two hours before exercise to ensure adequate hydration and to void any excess fluid3. The body has a natural mechanism in place for cooling itself—sweating. Though it is useful for cooling the body, sweating also causes a loss of fluids and sodium that are necessary to maintain hydration. For physical activity that lasts more than one hour, you should consume fluids during the workout3. The salt that is lost through sweat should be replaced with a sodium-containing beverage to adequately rehydrate. Ideally, the rehydration beverage will also contain carbohydrate, such as low fat chocolate milk or a sports drink, because the combination will increase fluid retention while replacing muscle glycogen stores that have been depleted as a result of exercise. A good indicator of hydration status is urine color. Light yellow-colored urine (similar to lemonade) is more indicative of adequate hydration, whereas darker yellow urine (similar to apple juice) generally indicates the need to drink more fluids. A final piece of advice about exercising in warm temperatures is to try and do so in shaded areas as much as possible while wearing loose-fitting, moisture-wicking, light-colored clothes to reflect sunlight. So lace up your tennis shoes, fill up your water bottle, and enjoy the rest of summer! 1 The American Physiological Society 2008
2 Journal of Applied Physiology 2006
3 American College of Sports Medicine 2007 | 
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