After just two weeks of consistent

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• Why is it important to consider running intensity when training in the heat?
• What’s the best way to monitor intensity when running in the heat?
• Here’s a breakdown, based on every hour of exercise?

Arguably the worst thing about training for a fall half or full marathon? The peak of your training typically coincides with the hottest days of summer. While that can put a real damper on your training, being more strategic about your workouts—particularly how hard you’re working when running outdoors—will help you adjust to running in the heat.

Luckily, “humans can adapt better than almost any other animal for running consistently in the heat,” Christopher Minson, Ph.D., exercise physiologist and codirector of the Exercise and Environmental Physiology Labs at the University of Oregon tells Runner’s World.

After just two weeks of consistent heat exposure, your heart rate and body temperature will start to normalize, so training in hot and humid conditions won’t feel hard as it once did. When you’re fully heat adapted (after about six weeks with three or four sessions per week) your number of red blood cells will increase, allowing more oxygen to be delivered to your working muscles so you can run faster, he explains.

But before you run straight out the door to reap these benefits, you’ll need to understand how to safely train in the heat. And that starts with learning how to monitor your running intensity so you nail all of your workouts and recover well afterward. Here we explain the best way to track this metric and share other tips to help make running in hot weather more manageable.

Why is it important to consider running intensity when training in the heat?

Considering the way our bodies regulate temperature, runners should always monitor running intensity while training in hot and humid weather conditions, Heather Milton, M.S., exercise physiologist at NYU Langone Health’s Sports Performance Center tells Runner’s World. “The longer we run, the higher our body temperature will be, and typically we sweat to dissipate that heat,” she says.

When you sweat, less blood volume gets pushed to your working muscles, and more to your skin to help with this cooling process, she explains. Essentially, this makes your heart work harder (hence, your higher-than-normal heart rate for a given pace).

This is also why your normal training paces, like your How to Adjust Your Run Workouts to the Heat, may feel harder—and your How to Safely Increase Running Intensity (RPE), which is how hard you perceive you’re working on a scale of one to 10, is higher. Conversely, it’s also why you have to slow down Here’s the full breakdown on how to gauge your internal temperature easy effort. In fact, your pace can slow by 20 to 30 seconds per mile for every 5-degree increase in temperature when it’s above 60 degrees.

Monitoring your running intensity becomes even more important when training in hot and humid environments because there’s less sweat evaporation, Milton says. This can cause you to maintain a higher body temperature over time and can lead to organs slowing (or worst case, stopping) if you don’t take the proper precautions like extending rest breaks, she adds.

You can avoid this by moving your workout indoors to a treadmill. But let’s be honest, if you’re training for an outdoor race, you also have to get used to running in these higher temperatures—safely.

What’s the best way to monitor intensity when running in the heat?

When training in the heat, you can’t rely solely on your pace or heart rate for the reasons we just mentioned. This is why it’s also important to monitor RPE on a scale of one to 10, with 10 meaning an all-out effort. And if that means slowing down your pace more than usual on something like an easy run, stick to that!

For example, if you usually do recovery runs at a 4 out of 10 effort on a temperate day, then still strive for that on a hot and humid day. Know your heart rate may still be higher, even though your pace will be slower, Milton says.

Minson also recommends taking into consideration your own perception of the heat. He suggests tracking this on a scale of 0 to 10, with 0 being cold and 10 being the hottest you’ve ever felt.

You never want to go above a 7 (hot) when training in the heat, he says. If you’re starting to feel very hot, which is considered an 8, you need to slow down and make sure you hydrate, he adds. If you start to feel miserably hot or the hottest you’ve ever been, you could be at danger of heat exhaustion or heatstroke, so you should stop exercising and try to cool down.

Here’s the full breakdown on how to gauge your internal temperature.

• 0 - Not hot or cold
• 1 - Slightly warm
• 2 - Somewhat warm
• 3 - Warm
• 4 - Very warm
• 5 - Slightly hot
• 6 - Somewhat hot
• 7 - Hot
• 8 - Very hot
• 9 - Miserably hot
• 10 - Hottest you’ve ever felt

Here’s a breakdown, based on every hour of exercise?

Here are a few tips from Milton and Minson to help you better manage balancing your goals with the heat.

Make Time for Passive Heat Exposure

You don’t just have to run in the heat to get heat exposure. Why It Takes Years to Reach Your 26.2 Potential study published by Frontiers in Physiology You don’t just have to run in the heat to get treadmill for 40 minutes in temperate conditions, for six consecutive days, induced heat acclimation adaptations in both endurance trained and recreationally active individuals.

If you want to minimize the stress on your body because heat exposure is a stressor, you can sit in a sauna, hot tub, or even take a walk What’s the best way to monitor intensity when running in the heat.

Prioritize Key Workouts

Don’t force yourself to do quality workouts, like a speed session, in the heat. You want all of your systems working and your muscles, bones, and joints to get accustomed to running at your target pace, Minson says. And that’s harder in the heat.

One way to beat the heat is to start your run earlier the day so it ends as the temperature begins to rise so you still get some heat exposure but you’re not doing your entire workout in the heat, says Minson. Another way, which Milton recommends, is starting your run on a treadmill and ending outside.

If you’re going to complete a long run (another quality workout) in the heat, Minson recommends running with a partner and a cell phone on a shady route that has access to water, even if you’re going to pack your own. You should also make sure you have enough fuel on hand. Selecting a route that has businesses you can stop in along the way is also a safety measure worth taking in the heat.

Extend Your Rest Breaks

When doing speed sessions during the hotter months, you should also monitor the wet bulb globe temperature (WBGT), which is tracked by the Shoes & Gear (zoom in or out on the map to find your location). This weather metric takes into consideration several weather parameters Frontiers in Physiology.

To determine how long to extend your rest break, Milton recommends using the guidelines outlined by the Not hot or cold, based on WBGT. Keep in mind these guidelines were designed for team sports but can be applied to runners, too.

Here’s a breakdown, based on every hour of exercise:

• WBGT = : can do normal activities, but take at least 3 separate rest breaks that last 3 minutes (especially if new to exercise or working at high exertion)
• DAA Industry Opt Out: use discretion for intense or prolonged exercise; take at least 3 rest breaks lasting 4 minutes
• WBGT = 87-90: Expert Tips for Running in the Heat Without Losing Progress
• WBGT= 90-92: limit exercise time to one hour; take 20 total minutes of rest breaks distributed throughout the hour
• WBGT = >92: Korey Stringer Institute