Fartlek Training for Trail and Ultramarathon Runners


By Darcie Murphy,
CTS Ultrarunning Pro Coach

Fartlek runs are fun, challenging, and useful for ultramarathon runners. And, of course, ‘fartlek’ is just a fun word to throw into conversation. A Scandinavian term coined in the 1930s by Swedish coach Gosta Holmer, fartlek translates to ‘speed play’ in English. And ‘playing with speed’ is an apt way to describe this style of unstructured but purposeful intensity training. Here’s how it works and how it can make you a faster, stronger runner.

More often than not, running should be fun. Sure, there are times we must rally all the motivation we can muster to get through a planned workout. However, if training is becoming a chore you may need to change things up a bit. A Fartlek workout is one approach to adding a lighthearted element to a rather challenging workout. What could be more fun than that?

What are Fartlek workouts?

Fartleks can be a highly effective strategy for ultrarunners. First, the term ‘speed’ in ‘speed play’ infers that this won’t be an endurance paced effort. Fartlek efforts include maximal or nearly maximal efforts, so anticipate elevated heart rate, breathing rate, and perceived exertion for these types of runs. The second term in the translation is ‘play’, which connotes that Fartlek efforts are inherently enjoyable. A maximal speed effort is fun? Absolutely.

Fartlek efforts are traditionally less structured than, let’s say, a 5×3 min Running Interval workout. However, the physiological benefits are similar because either way you’re accumulating time at RunningInterval intensity. These are not endurance sessions, nor are they threshold sessions. Fartlek is a V02 max development workout. The difference is that, instead of a strict time schedule, you’re using terrain or landmarks or personal cues to start and stop the VO2 max efforts.

The benefits of Fartlek workouts

The idea is to engage with your environment more than with your GPS watch. It has become normal in ultrarunning to be heavily, if not exclusively, dependent upon a device as a constant guide. However, learning to pace by perceived exertion is incredibly powerful for runners. Fartlek sessions are opportunities to tune into your body and the environment to tell you when it’s time to spring into action.

Runners can use Fartlek to intercept the technological feedback loop and relearn how to listen to internal cues. For many, over-reliance on technology has dulled your understanding and perception of physiological cues. If it feels unnerving or confusing to run without live data, that’s okay. Keep it simple as you begin.

How to run Fartleks

Fartlek running is limited only by the ultrarunners’ creativity. The aim is to develop environmental or situational cues that denote when it’s time to go hard and recover. It is not important for these cues to be evenly spaced. The lack of precise timing is part of the point. The duration of the ‘on’ or ‘hard’ portion can be anywhere from 20 seconds to half a mile, depending on the cues you choose to determine the duration of each effort. If you are truly running at or approaching VO2 max intensity, the efforts can only last a maximum of about 5-8 minutes. Here are a few ideas for using natural markers along your route:

  • Go block by block or from one fire hydrant to the next for an in-town run.
  • In a more rural setting electrical poles or fence posts can be your start and stop pinpoints.
  • Using trees, shrubs, cacti, or other natural markers along a trail may be your best points of demarcation for stopping and starting a Fartlek effort.
  • Fartleks can be done on uphill grades, so a rolling course may cue you to sprint the uphill portions and jog the descents.

How long should a Fartlek run be?

“How do I know when to start and stop Fartlek efforts? That is one of the most frequently asked questions about executing a Fartlek workout. People understand the concept, but sometimes struggle with execution. Here are some ways to determine when to start and stop the hard efforts:

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  • Try starting a Fartlek effort when your breath is slow enough to hold a conversation. From there, the end of each Fartlek may be the point at which you can speak only one to two words at a time.
  • Another effective Fartlek method to use as the start and stop sign is stride rate. For example, when you can maintain a stride rate that feels much faster compared to your normal endurance stride rate, you continue through the Fartlek. When you can no longer hold that very quick turnover it’s your cue to rest up and walk or jog slowly to recover before your next effort.
  • When you reach the point in your Fartlek workout in which you can no longer push yourself to that speechless point or your legs just won’t turn over quickly any longer, it’s likely time for a cool down.

Although the lack of structure is a key component of Fartlek running, it is important to maintain a sense of overall time-at-intensity. Typically, the hard efforts during a Fartlek run should total no more than about 20 minutes during a single workout. Sports science suggests a runner needs to accumulate a minimum of about 10 minutes at this intensity in a single session to elicit a training response. It’s okay to use those timeframes as a general guideline, but don’t get too wrapped up in time as a measurement since Fartleks are designed to be more free form than conventional speed workouts.

When to plan Fartlek runs

When is the best time to utilize a Fartlek workout? As we often say, it depends. During a strict, high volume/low intensity phase, or if your immediate objective is to improve your threshold running with highly structured Tempo Run workouts, Fartleks may not fit into your program optimally.

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On the flip side, Fartleks can be used effectively, in a variety of situations, to achieve both physical and mental benefits. For an athlete who may need to change things up after an extensive period with little variation in their training blocks, Fartleks can be a terrific psychological break. These workouts are also a fun and effective way to introduce speedwork for ultrarunners and trail runners who have little to no prior experience with speed sessions. Because of the lack of structure, ‘failing’ is less likely to occur because you’re simply experimenting with some faster running efforts.


Highly structured run training offers a wide range of benefits, and athletes also benefit from unstructured running. Fartlek workouts can be a great way to meld structure with creativity while weaving in playfulness. It can be a tool for understanding where you may be physically, and how ready you are (or aren’t!) to commit to a more regimented program. You can break up the monotony of any training program with Fartlek runs, and because they integrate a lot of intuition, it’s likely you may get ‘just the right amount’ of speed work on a given day. Jump in, give a few Fartlek runs a try and see what they have to offer.


Comments 3

  1. Excellent article. I tend to do too much “long and steady” on my runs, getting my intervals on the bike where I use repeat climbs. I will now add some fartlek. The focus on fun is especially helpful. Consistency is perhaps the most important element of performance. Fun training is consistent training. The same is true in races. My mantra during the swim of a triathlon is “reward”. I envision the joy I experience when I step out of the water: I get to bike and run!

  2. One of the better articles about fartlek. Living and training in Norway for several years when fartlek was still being taught and instructed in the manner Holmer founded, I found that perhaps the greatest benefit of fartlek was learning to listen to your body and how it was responding on any given day and what it needed. Well written explanation Jason on how to discover fartlek.

  3. I’m an amateur runner from Tanzania I really enjoyed reading this helpful paragraphs. My aim now is to run long runs no matter the pace!!

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