When working out in the summer, watch for the signs of dehydration and heat stroke. Choosing a later evening or early morning.

But this summer, as climate change continues to push Earth's weather to extremes, entire swaths of the U.S. have experienced record-breaking levels of heat.

So, is a daytime run or bike ride in hot summer weather OK for our bodies? Or are we risking heat exhaustion or — even worse — heat stroke (there's a big difference, as we'll get into further down).

The short answer is yes, it can be ok to exercise when it's hot if you take precautions. But you have to tread (or hike or jog) carefully. And keep an eye on local heat advisories — it's best to shift your workout indoors in air conditioning during extreme temperatures.

We asked two specialists in heat and exercise — Carol Ewing Garber, professor of movement science at Columbia University and Dr. Matt Leonard, attending emergency physician at Suburban Hospital, Johns Hopkins School of Medicine (both regular exercisers) — to discuss the science behind exercising in the heat, how to keep your body safe, and what to do if you suspect you or someone you're with has heat exhaustion or heat stroke.

1. Don't eat right before you head out

Wait, what? Doesn't our body need fuel to move? Yes, that's true, say Garber. A light meal is a great idea — just put an hour between eating and your workout in the heat. "It takes blood and energy to your gut to digest the food and that makes more body heat — not what you want when you're already hot," she explains.

If you had a heavy meal like a cheeseburger, she says, you'll want to wait two to three hours before your hot outdoor exercise, since that fat- and protein-rich meal will take even longer to move through the digestive process.

So should you eat after that hot run? No, Garber advises. Hydrate right away, but wait until you've cooled off to eat, since digesting food will delay getting your body back to its usual temperature.

2. Protect your skin – it's the body's cooling system

The skin is an "amazing self-cooling apparatus," says Leonard. "Your skin and subcutaneous tissues are incredibly designed to move warm blood away from your core to keep your vital organs cool. Any damage to your skin or the underlying tissue prevents your body from being able to air condition itself."

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If you must exercise when the the sun is high, dousing yourself with water, as this jogger did last month in steamy Washington, D.C., could help cool you down.

To protect your skin, start with sunscreen, he says. And consider wearing loose, lightweight clothing that blocks the sun, and include a hat. "The head has a large body surface area for cooling, and a hat provides shade so that area stays cool," he says.

The other reason to protect your skin is to avoid cancer, Leonard adds. "That's a great longer-term benefit."

3. Wear material that will help your body breathe

The type of protective clothing you wear can also help you stay cool, says Leonard. "Wear sweat-wicking athletic clothing that allows your skin to perspire and cool," he says, "and avoid materials like cotton that basically keep the heat close to your body."

Useful clothes needn't be fancy; inexpensive sportswear designed to wick sweat from your skin can be found at most major retailers.

Garber agrees that breathable clothing is important in hot weather, but says exposing more skin (as long as you also wear sunscreen, and avoid the brightest hours of the day) can be helpful, too. "Exercise clothes have gotten smaller and smaller," Garber says with a laugh, "which is actually good for high temperatures because the more skin you have exposed to the atmosphere the easier it is for sweat to evaporate."

4. Hydrate before, during and after exercise

Dehydration can really sneak up on you, says Garber. The best defense against dehydration is a good offense. "Make sure you are drinking water at least an hour before you head out to exercise," she says, adding to keep drinking while you're working out (Leonard says it's important to start getting hydrated even the night before).

Garber recommends replenishing what's lost during your workout by drinking somewhere between a half liter to a liter for every hour you're exercising in the heat.

And what should you be drinking? "If you're working out for an hour or less, nice cold water is the best choice because it is absorbed pretty quickly. If you're going to be at it longer than that, then consider a sports drink to replenish sodium and electrolytes."

How do you know if you're dehydrated? "Check the color of your urine," says Leonard. "That's the best gauge for internal status." Leonard says your pee should be close to clear and not deeply yellow or brown. He says to also take note how often you have to pee. Haven't had to go in a bit? That may be a sign you're dehydrated.

Leonard also warns about going overboard on the water which can lead to a condition called hyponatremia. "You see this in athletic events where competitors are excessively hydrating with electrolyte deficient sources like water, and that can lead to seizures, cardiovascular collapse and brain swelling."

5. Try more heat-friendly forms of exercise

Garber says that while she loves hiking and running, when it gets hot, she opts for sports that her body can handle a bit easier in the heat. "If the water is cool, swimming is a great choice on hot days and a good way to manage heat in general, because your body is stressed from heat even if you're not exercising."

Yoga is also a good alternative, she says, because it is really beneficial from a fitness standpoint but doesn't take quite as much energy as running or riding your bike.

6. Choose early mornings, evenings or shady routes

Both Leonard and Garber say that one of the simplest ways to keep your body temperature at a reasonable level when you're exercising on a hot summer day is to go out earlier in the morning than you might in other seasons, or later in the evening, when the air temperature is cooler.

"That midday sun can add as much as 20 degrees or more to the actual air temperature," says Garber. "You really have to be careful about that."

If you're set on that noon run, at least consider moving your normal run in the sun to a shadier route where you can stay cooler easier, says Garber.

7. Know the difference between dry and humid heat and take that extra water vapor into account

A dry heat is easier on your body, says Garber. "Your sweat is able to evaporate in a dry heat, and you are better able to keep your body temperature in that normal, healthy range."

But high outside temperatures in a dry climate can also be dangerous. "You don't have that cue and can become dehydrated."

In humid areas, it's easier to tell how much water you're using because you're probably sweating at least some — but high humidity carries its own risks. "It's harder in humid areas for your sweat to evaporate and that really impairs your body's ability to cool yourself off," she says. "If you're soaked in sweat, think of that as a reminder to your body that it is not able to cool itself as well and to be careful."

Before you head out when it's hot, always check the humidity, as well as the temperature, Garber says. "If it is humid out, then the real temperature stress on your body is much greater."

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