Published by PMR of NY & CT
The first hot, humid week of summer can turn a familiar run, bike ride or tennis match into a struggle. Exercising in the heat makes your heart work harder and your body sweat more as it tries to stay cool, and pushing through without a plan can lead to heat illness.
You don't have to move every workout indoors when the temperature climbs. Easing into the heat, picking the right time of day and drinking enough let most healthy people keep training outdoors, as long as they know the warning signs of heat exhaustion and heat stroke.
Why exercising in the heat is harder
Your body cools itself mainly by sweating and by sending more blood to your skin. During hot weather workouts, your skin and your working muscles compete for that blood flow, so your heart rate climbs higher than usual at the same pace. Humidity adds to the strain, because sweat doesn't evaporate well when the air is already damp.
A run that felt easy in spring can feel hard in July. Expect to slow down, and judge effort by how you feel rather than your usual pace.
Ease in with heat acclimatization
Your body adapts to heat with practice. Over about one to two weeks of regular exposure, most people start sweating sooner, lose less salt in their sweat and keep a lower heart rate and body temperature at the same effort. This process is called heat acclimatization.
- Keep sessions shorter and easier on the first hot days.
- Add time and intensity gradually over the next week or two.
- Ease back in after time away from the heat, since the adaptation fades.
Plan your workout around the heat
- Exercise in the early morning or evening, when temperatures are lower and the sun is less intense.
- Check the heat index, which combines temperature and humidity, before you head out.
- Choose shaded routes and loops that pass a water fountain or your car, so you can refill or stop early.
- Exercise with a partner when you can, so someone notices if you start to struggle.
Drink, dress and cool down
When exercising in the heat, start well hydrated, bring fluids and sip regularly rather than waiting until you feel very thirsty. For long or very sweaty sessions, a sports drink or a salty snack can help replace the sodium you lose in sweat.
Wear lightweight, loose, light-colored clothing that wicks sweat away, plus a vented hat and sunscreen. Afterward, cool down in the shade and keep drinking.
Who needs extra caution
Talk with your doctor about exercising in the heat if you:
- Are an older adult
- Have heart disease, high blood pressure, diabetes or kidney disease
- Take medicines that affect how you handle heat, such as diuretics (water pills), some blood pressure medicines, antihistamines or some antidepressants
- Have had heat exhaustion or heat stroke before
- Are pregnant, in which case your OB or midwife can advise you
- Are getting over an illness, especially one with fever, vomiting or diarrhea
Young athletes need frequent water breaks and coaches who know the signs of heat illness. If you are coming back from an injury, our sports medicine team can help you plan a gradual return.
Know the signs of heat illness
Heat illness can develop quickly. Stop exercising at the first sign of trouble.
Heat cramps and heat exhaustion
Heat cramps are painful muscle spasms during hard exercise in hot weather. Rest somewhere cool and drink water or a sports drink. Get medical help if cramps last longer than an hour, or if you have heart problems or follow a low-sodium diet. Heat exhaustion is more serious. Signs include heavy sweating, cool and clammy skin, a fast and weak pulse, nausea or vomiting, dizziness, headache, weakness and fainting.
Move to a cool place, loosen your clothing, put cool, wet cloths on your skin and sip water. Get medical help right away if you are vomiting, or if symptoms get worse or last longer than an hour.
Heat stroke is an emergency
Call 911 if someone has a very high body temperature (103°F or higher, according to the CDC), confusion, slurred speech, hot red skin that may be dry or damp, a fast and strong pulse, a seizure or loss of consciousness. While you wait, move the person somewhere cooler and cool them quickly with cool water, wet towels or ice packs. Do not give the person anything to drink.
Frequently asked questions
What temperature is too hot to exercise outside?
There is no single cutoff. Humidity, direct sun, your fitness and how well you are acclimated all change the risk. The higher the heat index, the more you should shorten, slow down or move your workout indoors. When the National Weather Service issues a heat advisory or extreme heat warning, an air-conditioned gym, a pool or an early-morning walk is a safer choice.
Do you burn more calories working out in the heat?
Possibly a little, because your body works harder to cool itself, but the difference is small. Most of the weight lost during a sweaty workout is water that returns once you rehydrate. Wearing extra layers or a sweat suit to drop pounds in the heat raises your risk of heat illness without helping long-term weight loss.
Is it safe to exercise outside with asthma in the summer?
Often, yes, with some planning. Hot, sunny days can raise levels of ground-level ozone, an air pollutant that irritates the airways. Check your local air quality forecast, exercise in the morning when ozone is usually lower, and keep your rescue inhaler with you. Ask your doctor whether your asthma action plan should include medicine before exercise.
Keep training with PMR
If pain or an old injury is getting in the way of your workouts, Physical Medicine & Rehabilitation of NY & CT (PMR) can help. Our physical therapy team builds plans around your goals. Request an appointment and we will contact you to schedule your visit.
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