How Hot is “Too Hot” for Outdoor Exercise?

A guide to safe exercise in the heat and what you should know about heat-related illnesses

Coming into July, the hottest days of the year are just ahead. Temperatures are rising and humidity is becoming a major nuisance—that combination can make it tough to enjoy the outdoors. On top of the extreme weather, many people prefer to exercise outside, especially in the warmer months. Which leaves fitness fanatics wondering, how hot is “too hot” for outdoor exercise?

The World Health Organization recommends a maximum temperature of 75 degrees for “comfortable” exercise. Other sources typically agree, but it’s not the temperature that should be your main concern. Humidity is a greater threat because it affects your body’s ability to cool itself down. In dry heat sweat will evaporate, but on a humid day, your sweat is more likely to remain on your skin and drip. When sweat clings to your skin it’s harder for your body to maintain a safe temperature. That’s the simple answer.

The long answer is that it depends on a multitude of factors, primarily how your body works. You are the best person to answer the question of what conditions your body can handle, so it is most important to pay attention to how you feel. When you’re aware of the conditions outside, how your body is feeling and the symptoms of heat exhaustion and heat stroke, then you can decide your personal limits.

Heat exhaustion is when your body loses fluids or key nutrients due to exposure to heat. The symptoms of heat exhaustion are excessive sweating, a rapid pulse, pale skin, confusion, dizziness, muscle cramps, a headache, nausea and fainting. If you’re experiencing heat exhaustion, get out of the heat, drink plenty of fluid and take a cool shower or bath.

Heat stroke is the most serious type of heat injury, it can cause damage to the brain and other organs, and in some cases it is deadly. The condition most often affects older people, but has been a problem for otherwise healthy athletes. After prolonged exposure to heat and usually accompanied by dehydration, the body is unable to regulate internal temperature. It’s defined as heat stroke when the body reaches 105 degrees. Symptoms include a lack of sweating, a rapid pulse, shallow breathing, muscle cramps or weakness, a throbbing headache, nausea, vomiting, seizures and unconsciousness.

If you or someone else is experiencing heat stroke, get immediate medical attention. Call 911. While waiting for help, try to bring the body temperature down.

If you’re mindful of the symptoms, the conditions outside, and your body’s signals, you should have no problems enjoying outdoor exercise this summer.

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