Coaches Explain Which Running Workouts to Do Indoors in the Heat and Which to Adjust for the Outdoors

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Summer running sometimes offers up a serious challenge. As temperatures climb into the 80s, 90s, and even triple digits, your body has to work overtime just to stay cool—at the expense of your pace and performance.

The good news is you don’t have to suffer through every scorching day. Runner’s World spoke with two certified run coaches to gather intel on which workouts you should move inside on hot days and which ones to keep outdoors so you gain all the training benefits. Plus, we offer a set of smart, effective indoor treadmill workouts that can help you beat the heat—and keep your training on track.

How the Heat Affects Your Running

Elevated temperatures, even small jumps that may seem trivial to some, affect your body’s processes while you’re running and can result in dangerous consequences if you’re not prepared.

As the temperatures increase, your body works harder to cool you down. “The body’s main source of cooling itself during exercise is through the evaporation of sweat,” exercise physiologist Todd Buckingham, Ph.D., of PTSportsPRO in Grand Rapids, Michigan, previously told Runners World. As your core temp climbs, your body also redirects more blood to the vessels near your skin’s surface to help release heat.

Both of these cooling processes pull energy away from your working muscles, meaning every stride takes more effort as the heat increases. That’s why runners can expect to add 20 to 30 seconds to their mile pace for every 5-degree increase above 60 degrees Fahrenheit.

Health-wise, increased temperatures can lead to several heat-related illnesses including heat cramps, heat exhaustion, and heat stroke, which can be brought on by dehydration, as well as fainting and hyponatremia.

Steering clear of extreme heat can help your body perform more efficiently and train at its highest potential, while significantly reducing the risk of heat-related illness. But there are things you can do to withstand the higher temperatures, including slowing down and focusing on effort rather than a specific pace, as well as staying hydrated, fueled, and listening to your body when it needs to escape to cooler temperatures.

Types of Running Workouts to Keep Outside

You shouldn’t completely abandon outdoor running in the summer, says RRCA- and 80/20 Endurance-certified run coach Andrew Evans, who trains runners in Scottsdale, Arizona, the hottest city in the United States, according to 2024 data from Accuweather. Safely keeping both long runs and short speed workouts outdoors offers more benefits to runners than a fully indoor training plan.

A tried-and-true principle of racing is that you should never use a brand new piece of gear on race day because you don’t know how it will perform. The same goes for your training. You should allow your body to adapt to conditions that mimic those of your desired race, says Evans. If your goal is to run a marathon at the end of July or in a warmer climate this fall, you’ll benefit from doing your long runs outside to prep your body for the weather you’ll experience during the race.

Because you should complete long runs at a low intensity, you can adjust your pace to the heat, making sure to run at an effort that feels easy. (Just make sure you pay more attention to fueling and hydration to match the demands of more sweating!)

Short speed workouts, like 400-meter repeats with longer rest periods that allow you to cool back down between intense efforts, are also best done outside for a similar reason: They help your body learn to run fast when fatigued from the heat. It’s just essential to take precautions when pushing the intensity. For example, don’t worry as much about hitting exact paces, make sure you hydrate well before you step outside (and bring water with you), and take longer breaks if you need them.

Paying close attention to how you feel during your workout to manage the added stress of hot conditions is crucial, especially during long recovery intervals that are common in speed workouts, says Sean Fortune, New York City-based run coach and founder of Central Park Coaching.

If you’re feeling overly exhausted, dizzy, or disoriented at any point in your workout, stop what you’re doing and get out of the heat as soon as you can, Evans says.

Both experts said that because easy runs are both shorter than long runs and less intense than speedwork, they can be done safely inside or outside depending on three variables:

1. Goal race conditions: If your goal race is going to be hot (as mentioned above), keep at least one easy run per week outside to get accustomed to those conditions.
2. Heat severity: If temperatures are dangerously high, experts recommend shifting your easy run to the cooler morning or evening hours—or moving it indoors entirely—to avoid the hottest part of the day.
3. Personal preference: If you enjoy running in the heat and are safe and smart about your preparation and execution of hot-weather running, keep those easy efforts outdoors.

Research says that training in the heat even boosts cool-weather performance. According to a 2010 study conducted on 12 trained cyclists, heat acclimatization training improved time-trial performance, power output, blood plasma volume (which helps delays dehydration and helps maintain a stable heart rate), and VO2 max to similar extents in both cool and hot conditions.

This means that even if you have a goal race in the dead of winter, smart summer training still serves a purpose.

Types of Workouts to Take Indoors

Workouts that help boost speed endurance—your ability to run faster for longer—are crucial to a training plan, especially for half and full marathoners, because they usually involve extended hard-effort intervals. This includes tempo efforts and threshold runs.

However, both coaches note the combination of length and heightened intensity at high temperatures is exactly what skyrockets your risk of heat-related illness, which makes longer speed intervals ideal for an indoor environment.

“[Running inside is] easier on your body because you’re doing sustained harder efforts where the heat doesn’t play a role in degrading your performance or hastening your dehydration,” says Fortune.

These types of workouts are generally not as complicated either, so you don’t have to spend time fumbling around with the treadmill buttons and can focus on running.

As for what to do when you head indoors, we have three perfect workouts.

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3 Speed Endurance-Boosting Treadmill Workouts

The following three workouts, each conducted at or close to your tempo effort—sustained, comfortably hard running—will help you boost speed endurance while shielding you from the negative effects of excessive heat.

Each workout incorporates guidance using RPE (rate of perceived exertion) as a pacing tool. The RPE scale ranges from 1 to 10, where 10 signifies maximum effort.

Marathon-Paced Tempo

Why it works: Doing this workout on a treadmill eliminates pace fluctuations so you become more familiar with your exact goal marathon pace earlier in your training plan, says Fortune. Avoiding summer heat allows your body to focus all of its energy on sustaining your goal pace in the most efficient way possible so you’ll be able to maintain the same pace come race day.

How to do it:

1. 2-mile easy run warmup
2. 4-6 miles at goal marathon pace (4-5 RPE)
3. 2-mile cooldown

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Cruise Intervals

Why it works: “This workout provides many of the same muscular endurance benefits as a tempo run, but the interval structure keeps you more engaged over the course of an hour on a treadmill,” says Evans. This workout is helpful at just about any point in your training cycle.

How to do it:

1. 15-minute easy run warmup
2. 3 x 7 minutes at tempo pace (6-7 RPE) with 1-minute recovery jog (1-2 RPE) between
3. 15-minute easy run cooldown

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Incline Workout

Why it works: If your goal race includes an elevation gain, you can avoid the summer heat and still get your hill training! Running on the cushioned belt of a treadmill gives your joints a break from high-impact road training while still giving all the benefits of hills. “This workout targets your glutes and quads, enabling you to build muscular strength and power in a manner that is less stressful on the legs when performed on a treadmill with incline,” says Evans.

How to do it:

1. 15-minute easy run warmup (0% incline)
2. 3 x 5 minutes at tempo pace (2-4% incline; 6-7 RPE) with 3-minute recovery jog (0% incline; RPE 1-2) between
3. 15-minute easy run cooldown (0% incline)

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