Man does a Fartlek run while running outside

© BONNINSTUDIO/Stocksy United

Pro Athletes Rely on This Training Method to Increase Their Speed—and You Can Do It, Too

Reduce the boredom of long runs (and improve your fitness) with this type of interval training.

By Eric ArnoldDecember 4, 2023


Several years ago, I had a roommate who, after leaving a bar at 2 AM, realized he wasn’t in a state to drive himself home. He started walking and soon decided that the 10-mile journey would be more enjoyable if he walked for one gap between telephone poles along the road, then sprinted for two. He did this for the next 90 minutes or so before arriving home. While he didn’t realize it at the time, he had just completed his first-ever Fartlek run—a method of training that endurance-focused athletes rely on as an essential aspect of their workout routines.

Fartlek training, which translates from Swedish as “speed play,” is essentially free-form interval training. You alternate back and forth between a faster pace and a slower one to boost your overall fitness. Unlike traditional interval training, in which you follow a structured workout, a Fartlek allows for flexibility. You listen to your body, pushing yourself for as long as you can—before dialing it back and recovering.  

What Is a Fartlek Run?

“At a high level, it's just unstructured speed,” says Peloton instructor Matt Wilpers. “So it's a little bit fast, a little bit slow, a little bit fast, a little bit slow.” The trick, though, is to make sure you vary the lengths of your speed bursts, depending on what’s comfortable for you. Maybe, Matt says, you do a two-minute burst, then rest, then three minutes, rest again, then another two-minute burst—or perhaps raise it to four. Embracing inconsistency is at the heart of Fartlek training, and the beauty is that you can do it anywhere. You can measure bursts by city blocks, time, or laps around a track. And it’s not limited to running. You can also do Fartlek training on a bike, on a rower, or while swimming laps in a pool. Fartlek training is exercise agnostic.

Matt points out that Fartlek is just one training method that you can mix in with other types of workouts. On their own, Fartlek runs aren’t likely to unleash a new level of fitness. However, they can play a role in helping you reach your overall goals—particularly if you’re trying to make a comeback. 

“It’s really effective if you have someone who is in a rut or recovering from injury and isn’t really advancing in their workouts,” says Phillip Vardiman, an associate professor at Kansas State University who has a PhD in kinesiology. Vardiman, who has worked as an athletic trainer for USA Track and Field, says Fartlek training can also be beneficial for cardiovascular rehab patients because it stresses the heart to gain efficiency and effectiveness. “That’s the main key,” he says. “This is a different way of stressing it by incorporating different levels of speed.”

The Benefits of Fartlek Training

There are two great benefits to Fartlek training, beyond stressing your heart and other muscles in new and different ways. The first is combating boredom, especially during long runs. 

“I had a coach where when we would run as a pack together, we’d run past a tree or a stump, and he’d say, ‘Hey, Matt, remember that stump? Go back, touch it, come back,’” Matt says. “So the group keeps on running in one direction, and I have to sprint back and find the stupid stump and catch back up with the group.”

Similarly, Vardiman remembers a stationary bike training game he and his friends would use during the winter months. They’d put the NCAA basketball tournament on a TV, maintain an endurance pace, and then do sprints whenever the ball wasn’t in play. So fouls, TV timeouts, and other stoppages became short periods when they’d increase resistance or boost their cadence from 80 to 120 revolutions per minute. “It was the worst idea in the world, but it was really challenging for us,” he says. He credits this type of Fartlek work with helping increase his overall speed on the bike. (Psst: You can try this method out yourself while streaming NBA League Pass on your Peloton Bike.)

The second benefit, Matt notes, is that Fartleks are a helpful way to introduce someone to a new type of exercise. “Fartleks are good for anyone getting into running who has maybe never done speed work before,” he says. “It’s just you get to go in and go out, go in and go out, all in an unstructured way.”

And, as you do, your body will learn along with you. Vardiman explains that when you start a surge, you increase your stride rate and length, so your body learns to adapt and become more efficient at that fast pace. “You’re increasing your range of motion and recruiting new muscles to support the higher intensity,” he says. “After doing a few workouts, you develop neuromuscular patterning and muscle recruitment patterns that help you improve at that speed.”

That’s true regardless of whether you’re just starting out or identify as an elite runner. Vardiman says that the track and field coaches he works with at the collegiate level use Fartlek training to increase aerobic fitness, lactate threshold, and confidence in their athletes.  

Woman takes a break during a Fartlek run

© Rob and Julia Campbell/Stocksy United

How to Do a Fartlek Run

Both Matt and Vardiman are quick to point out that Fartlek runs are, by no means, a magic solution for building your running fitness. At most, you should incorporate just one or two Fartlek runs into your training each week. Both of them stress the importance of listening to your body while completing them, as well as mixing up the time or distance of your surges as you go. 

“Make sure that you’re doing some longer efforts—maybe two-, three-, and five-minutes—depending on what’s comfortable to you,” Matt says. “Just make sure you’re not doing all short bursts.”

The other reason for exercising restraint is that you will quickly feel the effects of Fartlek training after your first few tries—and not in a good way. “Any time you’re introducing a new type of exercise to your routine, you should know, you will likely get sore from it,” Vardiman says. This is because when you increase your stride rate and length, you’re not only recruiting different muscles but also stressing them, along with your tendons and bones. Your body also has to adjust its energy system to make your runs more efficient, Vardiman adds. 

However, if you ease your way in and don’t do more than one or two Fartlek runs per week (and work your way up to longer and more varied speed bursts over time), you can minimize any negative effects.

How to Do a Fartlek on a Treadmill

One of the other great advantages of a Fartlek run is that, if the weather outside isn’t cooperating with your training schedule, you can just hop on the Peloton Tread. Increase your speed, incline, or both for various amounts of time before returning to your endurance pace.

You can practice this method on your own or find a Peloton class that seems like it fits the bill. Look for longer interval runs, such as this 60-minute class from Becs Gentry, or perhaps an endurance run, such as this 60-minute one from Matt. In both types of classes, you can modify the speed bursts, based on your personal fitness level, goals, and how your body feels. While a Peloton class is likely to be more structured, you can dial up the Fartlek-ness as you see fit.

And therein lies the beauty of the Fartlek. Not only is it fun to say (and watch people’s facial expressions upon hearing the word for the first time), you can tailor each run to suit your style.

“It's not supposed to be very structured,” Matt says. “It can be kind of fun.”


Level up your inbox.

Subscribe for a weekly dose of fitness, plus the latest promos, launches, and events.

By providing your email address, you agree to receive marketing communications from Peloton.

For more about how we use your information, see our Privacy Policy.