If you’ve ever sprinted to the next lamppost, jogged to the corner, then pushed hard up a hill — all in the same run — you’ve already done a fartlek. You just didn’t know what to call it.
Fartlek (pronounced FART-lek) is one of the most effective and most misunderstood tools in running. It’s been used by Olympic champions and weekend joggers for nearly 90 years. And once you understand how it works, it will change the way you think about speed training forever.
This guide covers everything: what fartlek is, where it came from, how it differs from intervals and tempo runs, what it does to your body, and exactly how to start doing it — regardless of your current fitness level.
What Does Fartlek Mean?
The word fartlek comes from Swedish. Fart means speed. Lek means play. Put them together and you get speed play — which is exactly what fartlek training is.
It was originally written with a capital F, as a proper noun coined by its creator. Today it appears in lowercase, has been adopted into the vocabulary of runners worldwide, and reliably causes a small laugh the first time anyone hears it.
The name matters because it captures the philosophy. This isn’t rigid, stopwatch-driven interval training. It’s playful. It’s flexible. The pace changes when you decide, based on how you feel, the terrain ahead, or simply because a hill is coming. That spirit of play is built into the name itself.
The Origins of Fartlek: A Brief History
In the late 1930s, Swedish athletics was struggling. Finnish runners had dominated distance events for a decade under the legendary Paavo Nurmi, and Sweden’s national coach Gösta Holmér needed a new approach.
Holmér’s innovation was deceptively simple. Rather than separating speed work and endurance training into separate sessions, he blended them. Runners would head out into the pine forests around Stockholm, running hard up hills, recovering on the flat, then surging again whenever the terrain or mood demanded it. The whole session was continuous — no stopping, no walking, no track required.
The approach worked. Swedish runners began competing at the highest level of international distance running. Word spread. By the 1940s, the method had reached North America and was being adapted by coaches everywhere.
In the 1960s, New Zealand’s Arthur Lydiard — arguably the most influential running coach of the modern era — incorporated fartlek-style workouts into the training programs that produced Olympic gold medalists. His athletes ran fartleks over both flat and hilly terrain, using natural markers rather than stopwatches to govern their efforts.
Today, fartlek is standard practice for coaches at every level, from youth cross country programs to professional marathon training groups. The technology has changed — GPS watches, heart rate monitors, training apps — but the core principle is the same as Holmér’s pine forest runs: go hard when it feels right, recover when you need to, keep moving.
What Fartlek Training Actually Is
At its core, fartlek training is continuous running that alternates between faster and slower paces, with the transitions governed by feel rather than a fixed timer.
A typical fartlek session looks something like this:
- Warm up with 10–15 minutes of easy jogging
- Run hard to the next intersection, then recover at an easy jog until your breathing settles
- Surge again up the hill ahead, then recover on the descent
- Pick up the pace for two minutes, back off for two minutes
- Continue this pattern for 20–40 minutes
- Cool down with 10 minutes of easy running
There is no prescribed number of reps. No fixed rest intervals. No target pace per mile. The runner — or the terrain — decides when to push and when to back off.
This is what separates fartlek from other forms of speed training, and it’s also what makes it uniquely valuable.
Fartlek vs Interval Training: What’s the Difference?
This is the most common question, and the answer is simpler than most people think.
Interval training is structured. You run a defined distance or time at a defined intensity, then stop (or walk) for a defined recovery period. Example: 6 × 800 meters at 5K pace with 90 seconds of complete rest between each rep.
Fartlek is unstructured. You run continuously, speeding up and slowing down by feel. The recovery periods are active — you’re still jogging, not standing still. There’s no prescribed pace, no measured distance per rep, no fixed rest.
The practical consequence is significant. Because fartlek uses active recovery (jogging) rather than passive recovery (standing or walking), your heart rate stays elevated throughout the session. You accumulate more time at elevated intensity across the full workout than a traditional interval session provides.
This doesn’t make fartlek better than intervals — it makes it different. Most serious runners use both. Intervals are precision instruments for specific physiological adaptations. Fartlek is a flexible, lower-stress way to build fitness without the mental load of a structured track session.
Fartlek vs Tempo Run: Another Common Comparison
A tempo run (also called a threshold run) is a sustained effort at a single pace — typically around your lactate threshold, or the pace you could maintain for roughly an hour of racing. It’s steady, controlled, and deliberate.
Fartlek, by contrast, uses multiple paces across a single session. You might surge above tempo pace, recover below it, and surge again. The variability is the point.
Where tempo runs build your ability to sustain a specific race-relevant pace for extended periods, fartlek builds adaptability — your body’s ability to handle repeated changes in intensity. Both have distinct value. For most recreational runners, the lack of rigid structure in fartlek also makes it more sustainable psychologically over the course of a long training cycle.
What Fartlek Does to Your Body
This is where it gets genuinely interesting. Fartlek is not just a training style — it produces specific, well-documented physiological adaptations.
It improves VO2 max
VO2 max is the maximum volume of oxygen your body can consume and use during exercise. It’s one of the strongest predictors of endurance performance. The fast surges in a fartlek session force your cardiovascular system to work near its ceiling repeatedly. That repeated exposure — week after week — pushes that ceiling higher. Eight weeks of consistent fartlek training has been shown to produce significant improvements in VO2 max in runners across multiple fitness levels.
It raises your lactate threshold
Your lactate threshold is the exercise intensity at which lactic acid begins accumulating in your bloodstream faster than your body can clear it. Running at around 80–85% of full effort for a cumulative 15–20 minutes per session is enough stimulus to raise this threshold over time. A well-designed fartlek session naturally accumulates this volume across multiple surges — without you having to track it deliberately.
Raising your lactate threshold means you can run faster before fatigue sets in. For competitive runners, that translates directly into race performance. For recreational runners, it means your usual pace starts to feel easier.
It trains both energy systems simultaneously
Most training methods target one energy system at a time. Easy runs develop your aerobic base. Track intervals push your anaerobic capacity. Fartlek does both in a single continuous session — aerobic during the easy recovery phases, anaerobic during the hard surges. This dual stimulus is one of the reasons fartlek produces broad fitness gains efficiently, particularly for runners who don’t have time to separate speed work and base training into different days.
It builds mental resilience
Racing is rarely even. Competitors surge. Hills appear. The pace shifts without warning. Fartlek training is the closest simulation of this reality. By practicing repeated accelerations and decelerations, you train your mind — not just your legs — to handle unpredictability. Runners who do regular fartlek sessions consistently report feeling more composed and in control during races when the pace goes off-script.
It improves running economy
Running economy is how efficiently your body uses oxygen at a given pace — the running equivalent of fuel efficiency in a car. Varied-pace training produces subtle adaptations in stride mechanics, cadence, and muscle recruitment patterns that steady-state running does not. The alternating demands of fartlek essentially teach your neuromuscular system to be more efficient across a wider range of speeds.
Types of Fartlek Training
Fartlek exists on a spectrum from completely unstructured to highly organized. Here are the main formats you’ll encounter.
Classic (unstructured) fartlek
This is Holmér’s original vision. Head out for a run, let the terrain and your energy levels dictate the pace. Sprint to the next tree. Jog until you recover. Push hard up the hill. Back off on the flat. No watch, no plan, no target pace — just feel.
Best for: base-building phases, mental freshness, trail running, runners who find structured sessions draining.
Landmark fartlek
Use environmental cues as your markers. Sprint to the next stop sign. Recover to the second lamppost. Push hard around the block. This is the most common urban variation and requires no technology whatsoever.
Best for: city runners, beginners, anyone who wants light structure without a watch.
Time-based fartlek
Use your watch to govern effort periods — but still run continuously. Example: 1 minute hard, 2 minutes easy, repeated 8 times. This sits between classic fartlek and true intervals. You control the effort duration but there’s no stopping.
Best for: runners who want more consistency in their training stimulus while keeping the flexible, continuous nature of fartlek.
Mona Fartlek
Named after Australian distance runner Steve Moneghetti, this is a precise 20-minute structured format: two rounds of 90 seconds hard/90 seconds easy, followed by four rounds each of 60/60, 30/30, and 15/15. The effort periods become shorter and faster as the session progresses.
Best for: intermediate to advanced runners who want a classic, proven fartlek protocol.
Pyramid fartlek
Surges increase and then decrease in duration across the session: 1 min, 2 min, 3 min, 4 min, 3 min, 2 min, 1 min — with equal or shorter recovery jogs between each. The middle effort is the hardest.
Best for: runners preparing for races who want to practice sustaining effort as fatigue builds.
How to Do Your First Fartlek Run
You don’t need a track, a GPS watch, or a training plan. You need about 30 minutes and a pair of running shoes.
Here’s the simplest beginner fartlek:
- Start with 10 minutes of easy jogging to warm up — conversational pace, no effort.
- When you feel ready, pick up the pace to something that feels comfortably hard — maybe a 7 out of 10 effort. Hold it until you reach the next intersection, or for about 60 seconds.
- Drop back to an easy jog. Recover until your breathing feels normal again — probably 90 seconds to 2 minutes.
- Surge again. Recover again. Repeat this for 15–20 minutes.
- Finish with 10 minutes of easy jogging to cool down.
That’s it. The whole session takes about 35–40 minutes and costs nothing.
A few principles to keep in mind:
Run by feel, not pace. Your GPS watch can tell you how fast you’re going, but fartlek is about learning to run by effort. Ignore the pace number on your watch. Ask yourself: how hard does this feel?
The recovery matters as much as the surge. Don’t push the recovery jog. The point is to arrive at the next surge ready to run hard again. A jog that’s too fast bleeds into the next effort and dilutes the whole session.
Start shorter than you think you need to. Most beginners who try fartlek for the first time go too hard too soon in the surges and too fast in the recoveries. Err on the side of conservative. You can always add more.
At least half the session should be easy. Fast running should make up no more than 40–50% of a fartlek session by time. The rest is recovery jog or warm-up/cool-down. Don’t turn it into a tempo run.
How Often Should You Do Fartlek Training?
For most recreational runners, one fartlek session per week is enough — and highly effective. Replace one of your regular easy runs with a fartlek and you’ll notice improvements in fitness within four to six weeks.
For intermediate runners training for a 5K, 10K, or half marathon, fartlek works well as a complement to one tempo run or interval session per week. The two methods stress the body differently: fartlek is more variable and mentally lighter, intervals are more precise and physically demanding. Running both across a training week provides a fuller stimulus.
Advanced runners and those with coaches often use fartlek strategically during base-building phases — before the structured track work begins — and then reintroduce it every three to four weeks during race-specific training to give the body a break from the precise demands of interval sessions.
The only real guideline: treat fartlek like any hard workout. Give yourself at least one full easy day before and after. Don’t run two intense sessions on consecutive days.
Fartlek for Different Types of Runners
Beginners
Fartlek is arguably better for beginners than formal interval training. There’s no pace target to stress over, no fixed rest period to mismanage, and no track to navigate. The effort-based nature makes it self-regulating — if you go too hard, you simply recover longer before the next surge. It’s almost impossible to do fartlek wrong.
Runners training for a 5K or 10K
Short, sharp surges at 90–95% effort are the core of 5K and 10K fartlek sessions. The goal is to accumulate time near VO2 max pace without the mental load of counting track laps. A session of 8–10 one-minute surges with equal recovery accomplishes this efficiently and is genuinely race-specific preparation.
Marathon runners
Longer fartlek efforts — three to five minutes at threshold pace, with shorter recovery jogs — simulate the variability of marathon racing better than steady-state tempo runs. Including fartlek in long runs (the final 30–40 minutes of a 20-mile training run, for example) builds race-specific fitness and mental toughness simultaneously.
Masters runners (40+)
The active recovery structure of fartlek makes it a lower-impact alternative to traditional intervals, which can stress tendons and joints more severely due to the dead stops and fast restarts. Fartlek allows continuous movement, keeps tissues warm throughout the session, and is easier to self-regulate based on how the body feels on a given day — which becomes increasingly important as recovery times lengthen with age.
Trail runners
Fartlek is native to trail running. Holmér designed it for forest paths, not tracks. Natural terrain — uphills, descents, technical footing — provides the stimulus variation that fartlek is built around. Running hard uphill, recovering on the descent, surging across a flat section: this is fartlek in its original form.
What’s the Bottom Line?
Fartlek training is not a gimmick. It’s been around for nearly 90 years, has produced world champions, and has solid physiological science behind it. It improves VO2 max, raises lactate threshold, trains both aerobic and anaerobic systems, builds running economy, and develops the mental resilience that racing demands.
More practically: it’s flexible, it requires no equipment, it can be done anywhere, and most runners find it genuinely enjoyable in a way that track sessions often aren’t.
If you’ve never tried a fartlek, your next easy run is the place to start. Pick a landmark 200 meters ahead and run hard to it. Jog until you recover. Do it again.
You’ve just done speed play. The rest is practice.
Sources
- Holmér, G. (1937). Fartlek training methodology. Swedish Athletics Federation.
- NSCA Personal Training Quarterly. Fartlek Training with Personal Training Clients. National Strength and Conditioning Association.
- McMillan, G. The Lost Art of the Fartlek. McMillan Running.
- Wikipedia. Fartlek. Updated 2024.
- Bhutada, A. et al. (2024). Effectiveness of 4-week Fartlek Training on Cardiovascular Endurance and Speed. International Journal of Health Sciences and Research, 14(10).
