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Exercise, hot weather can be a dangerous mix

A smiling young woman in a tank top stands in a sunlit field, arms raised in a wide pose

Take precautions against heat-related illnesses to make your outdoor workout safer and more enjoyable.

When the weather turns warm, it's great to be active outside. But when it gets really hot and humid, be careful.

Exercising in the heat can cause heat cramps, heat exhaustion and potentially deadly heatstroke.

A few safeguards can help you avoid these problems. The American College of Sports Medicine (ACSM) says drinking plenty of fluids, wearing the right clothes and exercising at the right time of day are among the best ways to beat the heat.

Drink up!

You need to drink enough water, sports drinks or fruit juices before, during and after exercise. The ACSM generally recommends drinking according to your thirst—no more and no less. Fluids help your body perspire, which cools the skin and keeps body temperatures at a safe level. Avoid very cold drinks because they can cause stomach cramps.

More isn't necessarily better. The ACSM suggests trying to drink as much fluid as you lose while exercising.

If your urine is clear or pale, you're probably drinking enough fluids.

Other tips

The American Council on Exercise and other experts list these additional strategies to help you stay cool:

  • Reduce your workout intensity, particularly the first few times you're in higher temperatures. It usually takes 7 to 10 days to get acclimated.
  • Take advantage of the coolest times of the day. Early morning and after sunset are generally the best times for an outdoor workout.
  • Don't overdress. Exposed skin cools faster than covered skin. Clothing should be lightweight, light-colored and loose-fitting. A hat is a good idea.
  • Use a broad-spectrum (protects against UVA and UVB rays), water-resistant sunscreen with a sun protection factor (SPF) of 30 or higher. Apply it 15 minutes before going outside. This can help prevent a sunburn, which limits the body's ability to cool itself. Reapply according to the directions on the package.
  • Keep track of the "heat index," a measure of how hot it actually feels when you factor in humidity. Take extreme caution when the heat index is 90 degrees or higher. (For a heat index chart, go to the National Weather Service website at

Watch for warning signs

Warning signs of a heat illness depend on how severe the problem is.

A mild heat illness (heat cramps) may cause painful cramps in the stomach, arm and leg muscles.

If you have these symptoms, stop exercising, gently stretch the affected muscles and drink cool water or an electrolyte solution that's low in sugar.

A moderate heat illness (heat syncope or heat exhaustion) may cause weakness, fatigue, fainting, a body temperature of 104 degrees, excessive thirst, decreased sweating, weakness, headache, frequent muscle cramps, and nausea and vomiting. If you or someone you're with has these signs and symptoms, the American Academy of Orthopaedic Surgeons (AAOS) recommends the following:

  • Move to a cool, shaded area.
  • Remove tight clothing.
  • Give fluids (if the person is conscious).
  • Apply cooling measures such as a fan or ice towels if body temperature is high.
  • See a doctor, particularly if the person has nausea or vomiting.

A severe heat illness (heatstroke) may cause signs and symptoms such as a core temperature greater than 104 degrees, nausea, seizures, confusion and disorientation. Unconsciousness and coma are also possible. Heatstroke can sometimes occur without preceding signs or symptoms of heat illness.

Heatstroke is a medical emergency. If someone has symptoms, the AAOS recommends calling 911 and trying to cool the person by removing as much clothing as possible, submerging them in an ice bath and putting ice packs on the armpits, groin and neck. You should keep trying to cool the person until help arrives.

Reviewed 9/15/2023

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