TrainingCardio and conditioning methods
Fartlek: Unstructured Speed Play Within a Continuous Run
Quick Intro
Fartlek is a Swedish word meaning “speed play”. It describes a continuous run, ride or swim in which you mix faster and slower paces without a fixed plan, picking up the pace for as long as feels right and then easing back. The session never stops, and the effort rises and falls as you choose.
The Idea in Plain Terms
Fartlek was developed in the late 1930s by Gösta Holmér, a Swedish Olympian and later national coach. Holmér’s aim was to combine speed work and endurance work in a single session, which gave Swedish distance runners a way to train both qualities without needing a track. Sessions were often done on trails and rolling terrain, using the landscape to decide the effort: surge up a hill, ease along the flat, pick up again to a landmark.
The structure is loose by design. Compare it with a standard interval session, where the work and rest times are set beforehand. In fartlek, you might run steadily for five minutes, surge for one, jog for two, surge for 30 seconds and continue in that way, guided by feel. A friend can also call the next surge, or a landmark can decide it, such as sprinting to the next lamp post.
Switching between paces trains the body to move between energy systems. Easy running leans on the aerobic system, which uses oxygen and can run for a long time. Surges draw more on glycolytic energy, which is fast and does not need oxygen, before the easy section lets the aerobic system recover. Because real demand in many sports also swings between fast and slow, fartlek is often described as a way to rehearse that variability.
A Worked Example
A 40-minute session could be laid out as follows, purely as an example:
| Time | What to do |
|---|---|
| 0 to 10 minutes | Easy jog as a warm-up |
| 10 to 30 minutes | Continuous running with surges: for instance 1 minute fast, 2 minutes easy, 30 seconds fast, 3 minutes easy, 2 minutes brisk, 2 minutes easy, and so on, chosen by feel |
| 30 to 40 minutes | Easy jog and walk to cool down |
The fast sections should feel hard but controlled, and the easy sections should allow breathing to settle.
What the Research Shows
Fartlek has less direct research than structured interval training, partly because it has no fixed protocol to test. What is known comes from the wider literature on interval and continuous work: mixing intensities within a session can improve aerobic fitness and the ability to run faster paces, and doing it informally is one way to get that mix. Claims that fartlek is better than structured intervals for any particular goal are not well supported.
The main practical advantages are about experience and access rather than proven superiority. It needs no track, no timer and no rigid plan, and the lack of structure can make the surges less intimidating than a fixed set of hard repeats.
Who It Suits
- Runners, cyclists and swimmers who find structured intervals dull or rigid.
- Beginners who want to experiment with faster paces gradually.
- Field-sport players who want conditioning that resembles the stop-start nature of their sport.
- Anyone training on varied terrain.
It is less useful for athletes who need to hit exact paces and track progress precisely, since the loose format makes comparison from one session to the next hard.
How to Use It
- Warm up with 10 minutes of easy movement.
- Start with a simple plan, such as alternating 1 minute brisk with 2 minutes easy.
- As confidence grows, vary the length and number of surges.
- Keep at least some of the session at an easy pace so that surges stay strong.
- Finish with an easy cool-down.
- Use it once or twice a week alongside easier sessions.
Common Misunderstandings
It is not random running. Surges still need to be genuinely harder than the easy sections, or the session turns into steady running.
It is not only for runners. Cycling, swimming, rowing and even hill walking can all be run as fartlek sessions.
It is looser than HIIT. The recoveries are active and unscripted, and nothing is timed.
FAQ
How hard should the surges be? Hard enough that conversation becomes difficult, though not an all-out sprint. The aim is repeatable effort across the session.
How long should a fartlek session last? Commonly 30 to 60 minutes including warm-up and cool-down.
Can beginners do fartlek? Yes. Using short, mild surges such as 20 to 30 seconds, with long easy sections, is a gentle way to start.
Is fartlek good for weight loss? It uses energy like any aerobic work. Results depend on total activity and diet over the week.
Where This Comes From
Fartlek is generally credited to Gösta Holmér, a Swedish coach, in the late 1930s, as described in running histories and coaching literature. Details on the physiological rationale follow standard exercise physiology texts.
Related to: HIIT, MICT, LISS and energy systems. Exercises that fit a fartlek session include Sprinting and Hill Sprints.