Key takeaways
- Fartlek means 'speed play' in Swedish — unstructured interval training done by feel.
- You mix faster surges with easier running continuously, without strict timed rest like formal intervals.
- It develops aerobic and anaerobic fitness and teaches pace changes — great for trail's variable terrain.
- Sessions are flexible: surge to landmarks, vary effort, and recover with easy running, not full stops.
Swedish, 'fart' (speed) + 'lek' (play).
What fartlek is
Fartlek — Swedish for ‘speed play’ — is a running workout that weaves faster bursts into a continuous run, done by feel rather than to a strict plan. You might surge to a distant tree, settle back to an easy pace, then push up the next hill. That blend of effort and play is what separates it from rigidly structured speedwork.
Fartlek vs structured intervals
Both alternate hard and easy, but intervals are precise — set distances, paces, and timed rests — while fartlek is loose and intuitive, with surges of varying length and active recovery (easy running, not standing still). Fartlek trains adaptability and pace sense; intervals train precision.
On a rolling trail, a runner warms up, then plays: hard to the top of each rise, easy on the descents, a 90-second surge along a flat straight, easy through the technical section — finishing a quality session that never felt like a rigid track workout.
How to do it
Warm up, then add surges by time, by landmark, or by terrain (the hills make natural intervals), easing to a comfortable pace between to recover. It builds both aerobic and anaerobic fitness and complements tempo runs and threshold work in a balanced training week.
The bottom line
Fartlek is the playful, flexible cousin of interval training: surge and ease by feel rather than by the stopwatch. It builds speed and stamina, sharpens your sense of pace, and fits trail running's uneven terrain perfectly — a low-pressure way to add quality and variety to your training without rigid structure.
Frequently asked questions
What is fartlek training?
Fartlek, Swedish for 'speed play', is a running workout that mixes faster surges with easier running in a flexible, by-feel way. Unlike formal interval training with precise timed repeats and rests, fartlek is unstructured — you might surge to a distant tree, ease off, then push again — making it both effective and playful.
What's the difference between fartlek and intervals?
Both alternate hard and easy efforts, but intervals are highly structured (e.g., 6 × 800m at a set pace with timed rest), while fartlek is loose and intuitive, with surges of varying length and intensity and active (easy-running) recovery rather than full stops. Fartlek emphasizes adaptability; intervals emphasize precision.
How do you do a fartlek workout?
Warm up, then during a continuous run add surges of harder effort — by time (e.g., 1–2 minutes hard), by landmark (run hard to the next bend), or by terrain (push the hills) — easing to a comfortable pace between them to recover. On trails, fartlek naturally fits the rolling, variable ground.
Sources
- Interval & speed training — American Council on Exercise
- Trail running training — American Trail Running Association