Heat and exercise: Keeping cool in hot weather

Stay safe during hot-weather exercise by drinking enough fluids, wearing proper clothing and timing your workout to avoid extreme heat.

By Mayo Clinic staff

Whether you're running, playing a pickup game of basketball or going for a power walk, take care when the temperatures rise. If you exercise outdoors in hot weather, use these common-sense precautions to prevent heat-related illnesses.

How heat affects your body

Exercising in hot weather puts extra stress on your body. If you don't take care when exercising in the heat, you risk serious illness. Both the exercise itself and the air temperature increase your core body temperature. To help cool itself, your body sends more blood to circulate through your skin. This leaves less blood for your muscles, which in turn increases your heart rate. If the humidity also is high, your body faces added stress because sweat doesn't readily evaporate from your skin. That pushes your body temperature even higher.

Heat-related illness

Under normal conditions, your skin, blood vessels and perspiration level adjust to the heat. But these natural cooling systems may fail if you're exposed to high temperatures and humidity for too long, you sweat heavily and you don't drink enough fluids. The result may be a heat-related illness. Heat-related illnesses occur along a spectrum, starting out mild but worsening if left untreated. Heat illnesses include:

  • Heat cramps. Heat cramps are painful muscle contractions, mainly affecting the calves, quadriceps and abdominals. Affected muscles may feel firm to the touch. Your body temperature may be normal.
  • Heat exhaustion. With heat exhaustion, your body temperature rises as high as 104 F (40 C) and you may experience nausea, vomiting, headache, fainting, weakness and cold, clammy skin. If left untreated, this can lead to heatstroke.
  • Heatstroke. Heatstroke is a life-threatening emergency condition that occurs when your body temperature is greater than 104 F (40 C). Your skin may be hot, but your body may stop sweating to help cool itself. You may develop confusion and irritability. You need immediate medical attention to prevent brain damage, organ failure or even death.
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References
  1. Tips for preventing heat-related illness. Centers for Disease Control and Prevention. http://www.bt.cdc.gov/disasters/extremeheat/heattips.asp. Accessed June 6, 2011.
  2. Howe AS, et al. Heat-related illness in athletes. American Journal of Sports Medicine. 2007;35:1384.
  3. Mechem C, et al. Severe hyperthermia (heat stroke) in adults. http://www.uptodate.com/home/index.html. Accessed June 6, 2011.
  4. Glazer J, et al. Management of heatstroke and heat exhaustion. American Family Physician. 2005;71:2133.
  5. Gomez J, et al. Environmental stress. In: DeLee JC, et al. DeLee and Drez's Orthopaedic Sports Medicine: Principles and Practice. 3rd ed. Philadelphia, Pa.: Saunders Elsevier; 2010. http://www.mdconsult.com/books/about.do?about=true&eid=4-u1.0-B978-1-4160-3143-7..X0001-2--TOP&isbn=978-1-4160-3143-7&uniqId=230100505-57. Accessed June 6, 2011.
  6. Laskowski ER (expert opinion). Mayo Clinic, Rochester, Minn. June 13, 2011.
HQ00316 June 25, 2011

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