You may not be ready to return to the gym just yet, but exercising in the heat is tough.

“We get rid of heat through the evaporation of sweat, and so if it’s really hot outside, that process is slower and your body has to work harder,” says Patrick Davitt, program director of health sciences at the University of the Sciences.

That doesn’t mean you should skip your workout. With a little mindfulness, you can still get your fitness on, and do so safely.

Here are some tips for working out outdoors when the weather is hot:

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Ease into it

The most important thing you can do is take time to acclimate your body, says Alexis Tingan, a sports medicine doctor at the University of Pennsylvania.

“We recommend using a two-week period to ease into the heat, so starting with a one-mile jog instead of three, and slowly amping up,” he says.

Best time to exercise

Temperatures peak between 10 a.m. and 3 p.m. Plan to avoid that window, ideally by several hours.

“It’s coolest between midnight and sunrise, so try to get out there before 7 a.m.,” says Tingan.

Rolling out of bed might not feel easy, but the earlier you do so, the fewer people you’re likely to encounter. For motivation, Suzanne Allaire, cofounder of November Project Philadelphia and multiple-marathon runner, recommends setting your clothes out the night before and finding an accountability partner. This can simply mean texting a friend to tell them your plans.

“Sometimes I’ll turn to social media and tweet that I’m going to get up and run. Other people will chime in, and we’ll check back in with each other,” Allaire says. And coffee can help, too. “We also just got this programmable coffee pot — when I smell the coffee, it makes me want to get up.”

Pay attention to humidity more than temperature

While 90 degrees might sound hot, it’s actually humidity levels to which you want to pay closest attention. Remember, your body cools itself down when your sweat evaporates, and humid conditions make evaporation harder.

“In high humidity, the sweat just stays on your skin, so your body has to work on overdrive,” says Tingan.

Because evaporation is key, wiping sweat off with a towel isn’t going to help. Don’t let a cloudy day trick you, either. If it’s extra humid, cloud cover won’t make much difference.

Hydrate early

Going into a summer workout dehydrated is one of the worst things you can do, experts say. Drink water throughout the day, not just before heading out. And remember, public water fountains may be out of commission, so plan ahead.

“The eight glasses of water rule a day is not the end-all-be-all, but it’s a good rule of thumb,” says Tingan.

A good hydration test is to check the color of your pee. It should look like a light lemonade. If it’s darker, drink more.

For longer workouts, consider weighing yourself before and after.

“If you weigh 180 pounds right before, and you’re 175 after, you just lost five pounds of water weight,” says Davitt. “Every pound is 16 ounces of water, and ideally you want to replace that within the next few hours.”

One tip is to fill a water bottle halfway and freeze it overnight. Top it off before you head out for your workout.

“Evaporation is the main way we lose heat, but the other one is conduction — if you touch something cold, it’ll pull the heat away from your body,” says Davitt.

Refuel with electrolytes

We lose electrolytes — essential minerals like sodium, calcium, and potassium — in our sweat. If exercising for more than an hour, refuel your electrolytes while working out.

Choose low-sugar options that you can add to your water, says Davitt. His favorite brands are Nuun and Generation UCan.

Dress smart

In the summer, cotton is not your friend.

“It holds water, which makes it not only harder to cool off, but more likely for you to blister and chafe,” says Ross Martinson, Philadelphia Runner owner and elite athlete coordinator for the Philadelphia Marathon.

Instead, go for fabrics labeled moisture-wicking, often found on spandex, polyester, or other synthetic-crafted clothes. These are quick-drying, sweat-absorbing materials.

Even with those, less is better.

“You want a large surface area for sweating and evaporating, so the more of your skin that’s exposed, the better,” says Tingan.

If you feel comfortable, work out in a sports bra or go shirtless. For a T-shirt, choose light colors, which reflect heat from the sun. And don’t forget sunscreen.

Running surfaces: Trails > concrete > asphalt

Pavement absorbs light and radiation and emits it as heat, so stick to sidewalks or grass when possible. Better yet, hit a trail an hour or two away from a city, where temperatures are almost always cooler. Cities have more buildings and roads, which absorb heat from the sun, and fewer plants, which cool the air.

Even within city limits you can find refuge on shaded trails, like those in Wissahickon Valley Park and John Heinz National Wildlife Refuge at Tinicum.

When running feels impossible, switch it up

The pandemic fueled an inspiring number of new runners. But jogging isn’t the only way to work out outdoors.

“I’ve been doing a lot more biking, which is great cross-training and creates a little more wind against you in the heat,” says Allaire. “It’s also easier to carry more hydration and snacks.”

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Swimming is one of the best summer workouts if you can find a place to go. And never underestimate YouTube, which offers a library of workouts, from yoga to body-weight classes, to try outside or in your air-conditioned home.

“If you don’t own weights, a gallon of water weighs 8 pounds, so put a gallon in each hand,” says Davitt. “Or you can get a 40-pound sandbag at Home Depot for $5 — one of the greatest and cheapest workout tools.”

Know the warning signs

If your body starts to cramp or you get a headache, you may be nearing your limits. Other signs include feeling weak, light-headed, nauseous, clammy, cold, and pale. If these symptoms occur, stop immediately, and try to cool off yourself off.

“Find shade, hydrate if you have water on you, and if you’re near home, go home and get by a fan, which will help the [sweat] evaporation process,” says Tingan.

How hot is too hot?

Most experts say that as long as you’re healthy, the climate around Philly almost never reaches a point where you shouldn’t exercise outside.

“There’s not a hard and fast rule, but use common sense,” says Tingan. “If it’s super hot, go for a walk, and avoid the hard workout.”

If you have an underlying condition, always consult with your doctor first.

Don’t beat yourself up about scaling back

Listen to your body. Heat and humidity may require you to decrease your intensity and volume, and there’s no shame in that.

“It’s important that we allow ourselves a little bit of grace, especially right now — few of us are training for anything,” says Allaire. “But set goals, and make them attainable. For me, if I say I’m going to run five miles today instead of 40 miles this week, I’m better at meeting it.”

This article has been updated.

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