For a rigorous, almost mathematically precise training plan, you can’t beat interval training. For similar results with a lot more fun and spontaneity, fartlek training offers a great alternative.

Fartlek was developed in the mid-1930s by a Swedish coach named Gösta Holmér. The word always provokes a giggle from English speakers. Translated from the original Swedish, it means “speed play.”

The “play” aspect of fartlek running is what separates it from other training methods. To be clear, this isn’t the type of play enjoyed by three-year-olds splashing with rubber duckies in a bathtub. There’s no free lunch in running. No training program produces results without serious dedication and application, not to mention lots of sweat.

Instead, with fartlek training, you run as hard as you want for as long (or as short) as you want, and only when you feel like it. Then you slow down or walk until you feel like going at it again. This is very different from interval training, where workouts are planned before you start running and there’s a prescribed distance and time for everything.

The great Swedish runners of the 1930s and 1940s conducted their fartlek workouts on soft, undulating pine-forest trails. They might begin one fast burst at the foot of a hill, or at the large boulder where the trail curved. The burst would continue until the runner felt it was time to stop. The distance didn’t matter, the time didn’t matter. The Swedes ran according to spontaneous effort, and felt that the pristine natural surroundings assisted them.

When Gunder Hägg and Arne Andersson set six world records for the mile in the early 1940s, the value of Swedish fartlek training was demonstrated. Soon athletes from Great Britain, Australia, New Zealand, and other British Commonwealth countries began to follow the fartlek program. They believed the free, undisciplined approach meshed well with the human spirit, while also connecting runners to trails, forests, and the natural environment. Man and nature combined. Who could improve upon it?

The beauty of fartlek running is its flexibility. You run slow and fast, slow and fast, as your soul and motivation direct you. While a Swedish pine forest can’t be beat as a training locale, you can also do fartlek on a long, straight US highway.

In this way fartlek becomes interval training, only without the stopwatch and clipboard. Fartlek is unscripted speed work, and capable of producing significant results. It remains one of the world’s favorite and most proven training systems.

  

Use the whole environment: Interval training is done on a flat, fast track. Fartlek training takes place in the real world, full of all its warts, wobbles, and natural landmarks. Run uphills, downhills, and sprints to the tree with the recently broken limb. Recover for 30 seconds, 3 minutes, or even 10 minutes. Go as you please. No two workouts could or should ever be the same.

  

Run short, run long: The best fartlek workouts are also the most varied. Run some very short, fast surges—much faster than you would normally run in 5K races, for example. Go longer on other surges, and use another pace, say your half-marathon or marathon pace.

You don’t have to alternate short and long in a specific formula. Mix them together however you want, or do a few more short bursts one day of the week, and a few more long pickups on another day. Don’t strive to do the same fartlek routine as the week before so you can compare total times. Throw comparisons out the window.

  

Go green: I have actually done fartlek training on the side of long, straight highways, as mentioned above. When circumstances force me to run alongside highways, this is how I make workouts more tolerable. But parklands are much more inspiring. I recommend you do fartlek workouts in your favorite green space. Treat yourself—it’s worth it.

I have noticed that fartlek running includes so much inherent variety that I can enjoy multiple laps of the same looping path. Normally I never do this. I get bored much too soon. But when I do a fartlek session in my favorite local park, I normally retrace the same 1.5-mile loop four times. It just happens to be the best, grassiest, smoothest, most rolling loop in the vicinity. Despite the repetitions, I find that time passes quickly, because I am doing different fartlek bursts at different parts of each loop.