Owen PalmerBy Owen Palmer

If you have ever wondered what is the difference between fartlek and interval training, the short answer is control. Interval training uses fixed, measured repeats at set distances or times with planned recovery, which makes it the stronger pick for runners who want precise pace targets and measurable progress. Fartlek, a Swedish term meaning “speed play,” mixes fast and easy running without a rigid script, so it suits runners who want speed work that feels looser, more enjoyable, and easier to fit into a route run.

Criterion Fartlek Interval Training
Structure Unstructured or loosely structured surges Defined repeats with set distances or times
Pace control Based on feel and effort Targeted paces, often by watch or track
Recovery Easy running between surges, length varies Fixed rest or jog, usually timed or measured
Best setting Trails, parks, hilly routes Track, measured loops, treadmill
Mental demand Low to moderate, playful Moderate to high, focused
Measurable progress Harder to track precisely Easy to compare week to week
Race-specific sharpening Good for general speed and fitness Strong for race pace and VO2 max work

Structure: Which Gives You a Clearer Plan?

Interval training wins on structure. A typical session might be 6 x 800 meters at 5K race pace with 400 meters of easy jogging between each repeat. You know the distance, the target pace, and the rest before you start. Coaches use this format because the variables are easy to adjust: add a repeat, shorten the rest, or pick up the pace by a few seconds per mile.

Fartlek is looser. A session might say “run 3 minutes hard, 2 minutes easy, repeat for 30 minutes,” or it might be entirely self-directed: pick a lamppost ahead and sprint to it, then jog until your breathing settles. The workout still has a purpose, but the shape changes with the terrain and how you feel that day.

Winner: Interval training for runners who want a plan they can follow exactly.

Pace Control: How Precisely Can You Hit Your Target?

Interval training is built around specific paces. Many runners use a GPS watch or a track lap counter to hold something like 5K pace or 1500-meter pace during each repeat. Because the effort is measured, you can check whether your fitness is improving by comparing splits over several weeks. If your 400-meter repeats at a given pace feel easier after four weeks, you have evidence of progress.

Fartlek relies more on perceived effort. You might run the “hard” segments at around a 7 or 8 out of 10 and the “easy” segments conversationally. This is useful because it keeps you responsive to fatigue, heat, and hills, but it is less precise. Two fartlek sessions can look very different on paper, even if both felt right.

Winner: Interval training for measurable pace targets. Fartlek is the better choice when you care more about effort than exact splits.

Recovery: How Do the Rest Periods Differ?

Interval rest is usually fixed. A standard recovery is a jog of 200 to 400 meters, or a walk or jog of 60 to 90 seconds for shorter repeats. Keeping recovery consistent helps you maintain quality across the set, which is why interval sessions are so effective at building the ability to sustain speed.

Fartlek recovery is flexible. You might jog for 90 seconds after a hard surge up a hill, then go straight into another surge without a set rest. This variability trains your body to recover while still moving, which mirrors the unpredictable demands of racing or trail running.

Winner: Depends on your goal. Interval training is better for controlled recovery. Fartlek is better for practicing recovery under changing conditions.

Best Settings: Where Should Each Workout Happen?

Interval training fits well on a track, where distances are exact, or on a measured loop. A treadmill also works well for intervals because you can set precise speeds and inclines. The controlled environment is part of the point.

Fartlek shines outdoors. Rolling terrain, park paths, and trails give you natural opportunities to surge uphill, cruise on the flats, and ease down. You do not need any equipment beyond running shoes, and you can change the workout on the fly. Runners who find track sessions tedious often find fartlek more enjoyable.

Winner: Fartlek for variety and outdoor running. Interval training for controlled, indoor or track-based sessions.

Fitness Goals: Which Builds Speed and Endurance Better?

Both methods improve speed, aerobic power, and lactate clearance, but they emphasize different things. Interval training is excellent for developing VO2 max and race-specific pace. Repeats at or slightly faster than goal race pace teach your legs and lungs to hold effort during a 5K or 10K. Coaches often program these sessions in the late base or build phases of a training block.

Fartlek builds a broad base of speed and aerobic fitness. Because the intensity varies, it can improve your ability to change pace during a race, surge on a hill, or respond to a competitor. It is often used earlier in a training cycle, or by runners who want speed work without the intensity of a full track session.

Winner: Interval training for race-specific speed. Fartlek for general fitness and changing pace.

Mental Demand: Which Feels More Sustainable?

Interval sessions can be mentally demanding. Watching the watch, counting repeats, and holding a target pace requires focus, and some runners dread the monotony of 10 repeats of the same distance. The payoff is clear progress, which keeps many runners motivated.

Fartlek is more playful and less rigid. Choosing your own landmarks and surges keeps the session engaging, which matters for consistency over months of training. If you tend to lose motivation with structured workouts, fartlek may help you stick with speed work long term.

Winner: Fartlek for mental freshness. Interval training for runners who enjoy measurable goals.

Measurable Progress: How Easy Is It to Track Improvement?

Interval training is much easier to track. Save your splits, compare the same workout every three or four weeks, and look for faster paces at the same effort or lower heart rates at the same pace. A GPS watch with lap data makes this simple. Our guide to Best GPS Watches for Interval Training covers the features that matter for this kind of analysis, including lap alerts and pace targets.

Fartlek progress is harder to quantify because the workout changes each time. You can still track total time, distance, and how the session felt, but you will not get the clean comparison interval data provides.

Winner: Interval training, clearly.

Gear and Equipment: What Helps Each Workout?

Interval training benefits from tools that make pacing precise. A GPS watch with lap alerts, a treadmill with speed settings, or a set of marked cones on a field can all help. Cones are particularly useful for creating measured sprint segments or shuttle-style intervals. Our roundup of 18 Best Training Cones looks at options that suit track and field sessions.

Fartlek needs very little. Running shoes and a watch for timing are enough. Some runners use a simple stopwatch or a music playlist with tempo changes to cue surges, which keeps the session lively without extra equipment.

For interval work, the following products are commonly used by runners:

For fartlek, a light, comfortable running shoe and a watch with basic timing are usually enough. Many runners choose the View on Amazon for everyday training runs where fartlek sessions often happen.

Winner: Interval training for precision tools. Fartlek for simplicity.

Which Should You Choose?

Use this quick guide to decide:

  • Choose interval training if you are training for a specific race and want to hit precise paces.
  • Choose interval training if you like measurable progress and want to compare workouts over time.
  • Choose interval training if you have access to a track or treadmill and enjoy structured sessions.
  • Choose fartlek if you run on trails, hills, or park loops and want variety.
  • Choose fartlek if structured speed work feels tedious and you prefer to run by feel.
  • Choose fartlek if you are early in a training cycle and want to build general speed without strict targets.
  • Combine both if you want the precision of intervals and the flexibility of fartlek across a training week.

If you are following a race plan, our guide to Training Plan for a 5K: A Step-by-Step Guide for Beginners shows where speed work fits. For a more advanced build, see Intermediate 5k Training Plan: 8 Weeks to a Faster 5K, which places interval sessions alongside steady and tempo runs.

FAQ

Is fartlek the same as interval training?

No. Both mix fast and easy running, but interval training uses set distances or times with planned recovery, while fartlek uses looser, effort-based surges that vary from session to session.

Which is better for a beginner, fartlek or intervals?

Many beginners start with fartlek because it is flexible and does not require pace targets. Once comfortable with consistent running, adding structured intervals can help build race-specific speed. A coach or experienced runner can help you choose the right progression.

How often should I do fartlek or interval workouts?

Most runners include one speed session per week, though some add a second during a race-focused build. Allow at least a day of easy running before and after hard sessions. If you have an injury or heart condition, consult a doctor or qualified coach before increasing intensity.

Can I do fartlek on a treadmill?

Yes, though it is less natural. You can vary speed and incline in timed segments, which mimics fartlek structure. Some runners prefer outdoor fartlek for the terrain changes that a treadmill cannot replicate.

Which builds speed faster, fartlek or intervals?

Interval training generally produces more targeted speed gains because you repeat specific paces and distances with measurable goals. Fartlek builds speed too, but its variability makes improvements harder to isolate. Both are valuable, and the best choice depends on your goal and how much structure you want.

Conclusion

The difference between fartlek and interval training comes down to structure and purpose. Interval training gives you measured repeats, target paces, and clear progress data, which makes it ideal for race preparation. Fartlek offers freedom, terrain-based variety, and a more relaxed mental load, which suits trail runners and those who prefer to run by feel. Most runners benefit from using both: intervals to sharpen race pace and fartlek to keep speed work enjoyable and adaptable. Start with the method that matches your goal this month, and adjust as your fitness and schedule change.

Owen Palmer

About Owen Palmer

Owen Palmer is part of our editorial team and reviews and edits our speed & interval running guides, checking product details against manufacturer specifications and owner feedback.