Experts Reveal How Hot Is Too Hot to Exercise Outside

Thanks largely to climate change, crazy-high temperatures in a lot of the country are the new normal. Average world temps were at their highest on record for two weeks this July, and Phoenix, for example, just hit 110-plus every single day for a couple of weeks in a row.

We should expect more of the same: Experts predict that the average global temperatures could soar another 2 to 10 degrees in the coming decades. The most recent figures show that heat-related illnesses kill 600-1,300 Americans a year, either through heat stroke or other conditions that are made worse by the spiking temperatures, according to the EPA.

What that means to folks who stay fit by walking, running, biking, playing pickleball or doing anything else under the sun: a greater chance of being hit by heat exhaustion or one of the more serious health calamities brought on by high temperatures, says Elizabeth Gardner, M.D., sports medicine expert and an associate clinical professor at Yale School of Medicine.

It certainly is a paradigm shift, but this is where were at, says Dr. Gardner, of the fact that we all have to do more to guard against heat exhaustion, heat stroke and other issues, even if were used to working out in warm climates. The fact that its been 120 in Phoenix for days doesnt make it any safer.

How hot is too hot to work out?

Google that question and youll get a big 90 up at the top of the search results, but thats just an estimate and only part of the story.

The problem with that number is that it doesn’t take into account the other factors that affect your bodys perception and experience with heat, says Dr. Gardner. We all know that 90 temperatures and 90% humidity in Connecticut or the Bahamas is not the same as 90 in Arizona with dry heat. It feels different, and the body is being stressed in different ways.

If the only info you have is the temperature, 80 to 90 F is the be-extra-careful zone, says Stefani Sassos, M.S., R.D.N., C.S.O., C.D.N., NASM-CPT, the Good Housekeeping Institutes Nutrition Lab Director, who is also a personal trainer. There are a lot of variables, so its hard to pin it down to just a number.

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Other factors to consider

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Here’s what to know about staying safe in the heat:

1. Trust your body. If you go outside and it just feels borderline uncomfortable, you should say Im just going to do a light workout or go indoors, says Sassos.

2. Think about your bodys ability to handle stress that day, says Dr. Gardner. Things like if you’re tired, under the weather, didn’t sleep well or are a little hungover all affect how well your body will handle the heat that particular day. In the end you want to leave a little in the tank to live to fight another day theres always tomorrow, she says. Thats not to say you should trade your sprint workout in 100 weather for sitting on the couch, but there are lots of other ways to get the benefits of working out. Think: Indoor cardio, Crossfit or yoga (not the hot kind), or go for a swim.

3. Work out early in the morning or in the evening, when its cooler, says Sassos. Avoid the middle of the day.

4. Wear wicking clothes. Lightweight performance clothes designed for sports in hot weather are key, along with a hat, shades and sun protection. Dont go in your old college t-shirt, which has zero wicking capacity, says Sassos. But be aware: Not all fabrics that claim to be moisture wicking actually are, says Lexie Sachs, the Good Housekeeping Institutes Textiles, Paper & Apparel Lab executive director. My trick is to take a drop of water and place it on the inside of the fabric the part that touches your skin. You should see that drop spread out wide quickly. If it beads up or doesnt spread then it wont manage your sweat well.

5. Hydrate before, during and after your workout. Obviously after is crucial, but try to bring a bottle with you, says Sassos. If its super hot or youre exercising for more than an hour, sip an electrolyte drink.

6. Dont push it. In high heat, try taking it a little easier, really gauging how your body feels and being okay with turning back a little sooner, says Dr. Gardner.

7. Know the signs of heat illness. If you dont feel right, stop and get someplace where you can rest, hydrate and cool down, says Sassos.

The warning signs of heat exhaustion include the following, according to the CDC:

• Heavy sweating

• Paleness

• Muscle cramps

• Tiredness

• Weakness

• Dizziness

• Headache

• Nausea or vomiting

• Fainting

Untreated heat exhaustion can progress to heat stroke, which can lead to permanent disability or death if not treated quickly. If you see someone with these signs, call 911 and move the person to a shady area and try to bring their temperature down as quickly as possible.