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Exercising in the heat: What you need to know

5 min read

With signs of Spring and warmer weather, the need to consider factors such as water intake and dehydration become more important.  Here in the good old Midwest, temperatures and humidity levels will continue to rise making it more and more difficult for the body to cool itself.  The body cools itself by sweating and during this process water is lost from the body.  Surprising amounts of water can be lost and it has been reported that the average person will lose around 1.5 to 1.7 liters of fluid every hour during exercise (REF).  When water loss reaches 1% of the person’s body mass (approximately one 20 ounce bottle of water for a  170 pound athlete) many aspects of performance begin to deteriorate and this downwards spiral increases as the amount of dehydration increases (REF).  The more dehydrated you become, the more your performance and health is impacted.

The best way to counteract the loss of body fluid is to regularly consume fluid before, during and after the exercise bout.  A key factor that many athletes do not fully appreciate is the fact that it is nearly impossible for you to drink enough during exercise to adequately hydrate yourself while you continue to exercise in the heat.  The problem here is simply that the stomach has a difficult time absorbing and releasing enough fluid from it at a rate that will allow for rehydration to occur (REF).  In other words, once you develop dehydration to any amount it is next to impossible to reverse its negative effects without stopping altogether.  If you are out playing a friendly game of soccer or shooting hoops this is no big deal, but if you are competing in a tournament or running a race or triathlon, this fact can have a big-time negative impact on how you will end up performing.

A negative impact on your performance is one problem, but very serious problems can also occur to your overall health.  Make no mistake about it, exercising in extreme heat and humidity can have life-altering outcomes as each summer you read media reports of high school or college aged athletes succumbing and sometimes tragically losing their lives to heat injuries caused by extreme summer temperatures.  Below is a quick summary of the things you need to consider to make sure you can enjoy outdoor exercise:

  • Clothing: This is a major consideration and all clothing, if possible, should be lightly colored, allow for rapid evaporation against the skin and have good ventilation.  This is easy for runners and cyclists, but can be a distinct problem for athletes who sport requires them to wear a uniform with protective padding.
  • Hydrate, hydrate, hydrate: When you know it is going to be hot and humid you need to take significant strides to make sure your body is packed full of water.  As much water as it can muster.  Some guidelines include drinking copious amounts of fluid the day before whether it’s fruit juice, water, or milk and to choose foods with a high water content as well such as fresh fruits and vegetables.  Your urine should be clear and there should be lots of it (see below for more on this).
  • Within 30 minutes of starting you should drink 1.5 to 2 cups of water or sports drink and then during exercise you should strive to drink 1.5 to 2 cups of fluid or sports drink every 15 to 20 minutes resulting in an hourly consumption of around 4.5 to 8 cups of water or sports drink.  Try to spread it, though, to prevent too much fluid from hitting your belly at once.
  • Have an idea of how much weight you lost during the exercise session and drink two cups of fluid for every pound you lose.  If you do not know how much weight you lost then drink liberally until your urine changes from a likely darker yellow or gold to a pale yellow or clear appearance.
  • Urine Color: As mentioned previously, monitoring your urine color can be used as a guide for how hydrated you are.  When you are well hydrated, you will produce more urine and its color will be light yellow or clear.  As dehydration progresses, the color of your urine will transition from a definite yellow to a darker yellow to a gold or orange to brown; the darker your urine becomes the less of it you will produce.  Always strive to keep your urine as clear as possible.
  • Acclimate: It is important to understand that working inside an office with controlled temperature and humidity does not challenge the body much regarding cooling itself.  Therefore, when you change into your workout clothes to go exercise in the middle of the day when temperatures and humidity are elevated this presents a significant challenge to cool your body.  Try to give your body a chance to acclimate to the more challenging conditions by getting outside regularly and exercising during the times when you plan to compete.
  • Warning Signs: Heat injuries can happen to everyone.  Certainly symptoms such as feeling extremely hot, dizzy and disoriented are worth mentioning, but if anyone persons begins to lose their feet or their lunch it is time for them to stop whether they want to or not.
  • Rapid Cooling: What do you do if you or a friend did overdo it?  First, stop what you are doing and get into an air conditioned building and if outside, a shady area by a building or under a tree.  If you can manage to get into a cool, shaded place with a little air moving that is even better.  If possible, drink cold water or sports drink until you begin to feel better.  Do not return to exercising.  If the person has unfortunately experienced some bout of weakness, passing out, nausea or gets sick, these are signs for more aggressive cooling.  The best bet is to have them get into a cold water bath up to their neck.  These are not always available so making ice packs from a cooler or soaking cold towels in an ice bath and placing them on the person’s neck, groin and armpits can help to cool the body.  These steps should be taken immediately.

Summertime is a great time of the year.  While higher temperatures and humidity levels can challenging the body’s ability to cool itself, taking a few extra precautions and paying attention to how you are feeling in combination with some common sense can help to prevent significant problems related to the heat.



  1. Armstrong, L. E. (2005). “Hydration assessment techniques.” Nutr Rev 63(6 Pt 2): S40-54.
  2. Burke, L. M. (2001). “Nutritional needs for exercise in the heat.” Comp Biochem Physiol A Mol Integr Physiol 128(4): 735-748.
  3. Sawka, M. N., L. M. Burke, et al. (2007). “American College of Sports Medicine position stand. Exercise and fluid replacement.” Med Sci Sports Exerc 39(2): 377-390.
  4. Sawka, M. N., S. N. Cheuvront, et al. (2005). “Human water needs.” Nutr Rev 63(6 Pt 2): S30-39.
  5. Speedy, D. B., T. D. Noakes, et al. (2001). “Fluid balance during and after an ironman triathlon.” Clin J Sport Med 11(1): 44-50.

The post Exercising in the heat: What you need to know appeared first on 1st Phorm.

Chad Kerksick PhD
Chad Kerksick PhD

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