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Heat and Humidity - Two of the BIggest Challenges To Stay Cool and Hydrated During Training and Rac


As we exercise, our bodies burn the calories that that we consume (i.e. carbohydrates, proteins and fats). It is the breakdown of these calories and muscle movement that causes heat to build up and raise our core body temperature initiating the demands of the body to maintain its ideal body temperature of 98.60 degrees. There are several ways that the body dissipates heat (skin and exhalation for example); however, the most complex system involves your ability to sweat.

Simply put, water molecules evaporate from your skin removing heart energy, leaving water molecules on your skin making you feel cooler. The endothermic process of converting liquid to a gas is beyond the scope of this article; however, the ultimate goal is to maintain your body’s ability to efficiently dissipate heat throughout exercise. What makes it difficult is dealing with elements that we don’t have any control over – heat and humidity.

On hot days when there is little difference between the skin’s surface temperature and the ambient air temperatures, the skin provides only small cooling benefits – increasing the importance of sweating to maintain your internal core temperature. In fact, above 95 degrees Fahrenheit you lose no heat at all from your skin – evaporation must to all of the work. Humidity decreases your body’s ability to evaporate sweat because the air is already saturated with water vapor, slowing the evaporation rate. Though you and your clothes may be saturated, it is not helping you in your cooling process – sweat must evaporate to remove heat from your body – plain and simple. It is this concept that makes hydration so important; if you don’t have enough fluids to produce sweat you will over heat guaranteed (along with the adverse side effects – performance and health wise).

On average, endurance athletes lose approximately 30-35 ounces of fluid per hour of exercise (the actual amount varies by body size, intensity levels and heat/humidity levels). There are numerous formulas floating around in the sports nutritional world regarding ideal food and fluid intake; however, keep in mind that there are three things that we need to evaluate regarding ideal performance nutrition: water intake, electrolytes and calories. It has been AEM’s experience working with hundreds of athletes that the best way to formulate an ideal nutritional strategy is through trial and error. This formula requires good documentation on behalf of the athlete to track what is consumed, your workout duration and intensity levels along with average paces and HR levels. AEM has a data acquisition form that can be used by AEM athletes to facilitate this research. If you would like a copy of this form, please contact Robb directly.

Tips for training and racing in the heat and humidity

Avoid over-hydrating on plain water Train at times that are relevant to your race (i.e. if you are going to start your run at 2:00 pm during a race, then practice running at this time dealing with the heat, humidity and sun burn) Wear only clothes that facilitate the evaporation process (avoid cotton at all costs) Cold fluids absorbs faster than warm fluids; use insulated bottles Backing off of the intensity every so often and pouring cold water over your wrists and neck will help relieve your body of internal heat Pay attention to body signs that things are not going well: dry chills, becoming lightheaded or queasy are all indications to stop. Be smart!

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