A true fartlek run, which literally means “playing with speed,” should be treated as an opportunity to explore different paces. However, many runners see it as a relaxed session where they occasionally speed up if they feel like it, holding that quicker pace only while it feels comfortable. In these cases, the workout often acts more like an extended warm-up than a session that challenges the body to adapt.
To get the most benefit from a fartlek run, include a wide range of surge lengths and intensities. Mix in short 10 to 20 second all-out sprints, medium 1 to 3 minute efforts at your one-mile race pace, and longer 5 to 10 minute segments at a 10k to half marathon effort. Practice moving smoothly between all these speeds, staying composed during the faster bursts, and using the variety to gently increase the pace during the longer segments. You can arrange these segments in any order or combination that feels right to you.
An effective fartlek session requires shifting gears again right after recovering from each surge, with the final quarter of the run providing a strength and endurance challenge as you continue to change paces under fatigue. When done properly, it usually calls for at least two days of rest or easy running afterward to allow full recovery.
Fartlek workouts should also be seen as flexible sessions. If you are dealing with fatigue, poor sleep, or unfavorable conditions, it is fine to run mostly at an easy pace with only a few moderate surges. But if you feel strong and ready, that is the time to push the pace.
