What Is a Fartlek? Plus 6 Other Super-Common Terms Every Runner Should Know

Even though running is an activity anyone can do with minimal gear, it’s got a whole set of its own terminology—which can feel intimidating or exclusive at times.

For example, do you know what a fartlek is? The term might sound funny—and has certainly been the, ahem, butt of plenty sophomoric jokes—but it’s actually Swedish for “speed play.” For this quick-paced workout, you’ll mix in intervals of fast and easy-paced running in no particular order. “The beauty of a fartlek workout is that it's unstructured,” says Shiva Douse, co-founder of running studio RacePace in Houston. “It takes away the pressure of focusing on specific pace or time. You could even do it without a watch!” 

To try it, first warm up by running at an easy pace for 10–15 minutes. Then simply throw in fast sections when you feel like it—go for a certain amount of time or a distance, like sprinting to a stop sign. You can’t really screw up this session, says Douse: “The only way to do a fartlek wrong is to not have fun with it.”

Here are 6 other terms you might hear while prepping for a race, hitting the track, or just meeting up with some friends for a few miles. 

1. Tempo run

A tempo run is a moderately-paced effort to work on your speed endurance. “This is arguably the most misunderstood term among runners,” says Douse. “It’s often used to cover any effort faster than an easy run.” Running at the correct pace, however, is key for reaping the benefits of a tempo run. “The goal of this workout is to go at an effort that is just below where lactate starts building up in your muscles.” Over time, your body learns to hold a faster speed for a longer period of time. 

To try it, warm up at an easy pace for at least 10–15 minutes, then pick up the pace to a speed that feels challenging but controlled for about 30–40 minutes. To dial into the right speed, aim for a clip between your 10K and half-marathon pace, suggests Douse. Finish with an easy cool-down.  

2. Threshold

This phrase refers to the lactate threshold—the speed where lactic acid (a compound formed with glucose is broken down) starts to rapidly accumulate in your muscles and slows you down. “It’s the line between sustainable and maximum effort,” says Douse. “By definition, you can't sustain an effort above the lactate threshold for an extended period of time.” For most runners, their threshold is somewhere around 80 to 90 percent of maximum heart rate. Tempo runs are also known as threshold runs.

3. Yasso 800s

Here’s one term you should get familiar with if you’ve got a marathon on the calendar. This speed workout, named for famed runner and coach Bart Yasso, is known to help predict your marathon finish time. You’ll do several (start with 5 and work up to 10) 800 meter intervals at a fast pace with a 400 meter recovery jog between each. The idea is to convert your goal marathon time in hours to minutes,” says Douse. If you’re aiming to run a marathon in 3 hours and 50 minutes, aim to run each 800 in 3 minutes and 50 seconds. “It’s not a perfect predictor, but many runners see a correlation between the time they can hold for this workout and their ultimate marathon time.”

"“It’s not a perfect predictor, but many runners see a correlation between the time they can hold for this workout and their ultimate marathon time.”

4. Negative splits

The negative split is the holy grail of distance running. The term simply means running the second half of a workout or race faster than you ran the first half. That’s easier said than done. “The challenge of  negative splitting is twofold,” says Douse. “One, you’re trying to put forth a higher effort after you've already tired; and two, you must be disciplined in the first half when you feel fresh and might otherwise want to go faster.”

To set yourself up for negative-split success, add some progression runs to your training schedule. Start a long run at an easy to moderate pace and every few miles, get a little faster—until you finish at your 10K or 5K pace.

5. Pronation

If you’ve stepped into a specialty running store or read a running shoe review, you’ve likely heard this term. It describes how your foot rolls from the outside to inside of the sole as you stride—and is totally normal. “This slight inward roll is a natural part of making contact with the ground,” says Douse.

However, if you overpronate or underpronate (AKA supinate), it could place unwanted stress on your muscles and tendons. For that reason, getting a gait analysis at a running shop (where an employee or coach watches you jog briefly, sans shoes) can be beneficial. Once you know how much your feet rotate as you run, you can choose the correct shoes to encourage proper form and slash your risk of injury.

6. Bonking

After a big race, you might hear a friend say they bonked or hit the wall. It usually comes into play for long distances like marathons and refers to that moment when your body feels tapped out and you don’t know if you can push through to keep going. “The physiology of bonking is your body's inability to efficiently generate fuel from its depleted sources,” explains Douse. “Typically, glycogen stores in your muscles—their go-to energy source—are sufficient to get through a workout.  But in extended periods of effort, these stores run out and our muscles begins to shut down.” 

One way you can help prep your body to push through that moment of bonking: Try depletion runs, when you work out without fueling so your glycogen levels are low, during your training to teach your body to burn fat for fuel.

Originally published November 1, 2017; updated October 1, 2018.

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