Fartlek—Swedish for speed play—can be as structured or as freeform as you wish to make it and can be done virtually anywhere: on the roads or off, flat ground or hilly terrain. The beauty of the workout is in its adaptability to a number of different environments. The duration and intensity of your faster pickups can vary or stay consistent throughout the workout, recovery can be set beforehand or adjusted on the fly if necessary and achieving a desired effort level always takes precedence over hitting a specific pace.

Cross-country runners, ultra-distance racers, road marathoners and anyone in between can benefit from some fartlek workouts in their training schedules. One of my favorite all-purpose fartlek sessions is what my college coach coined a “meat and potatoes” workout—meaning it’s basic, but effective—called the 5 x 5. It consists of five 5-minute pickups at a hard effort with 2 minutes and 30 seconds of easy jogging for recovery in between.

Why should I do this workout?

Plain and simple: because it’s tough! When you strip it down, the 5 x 5 Fartlek is an effective workout that helps you build strength and speed, as well as the confidence to maintain a hard effort in the latter stages of a race. For all but the fastest runners, 5 minutes is less than a mile of hard running. You’ve got this!

How hard is hard?

That’s ultimately up to you, but 5K-10K race effort—for this workout I recommend ditching the GPS and opting for a basic stopwatch so as not to get concerned with hitting exact splits—is a good target to aim for on the 5-minute pickups. Don’t worry too much about pace in this workout—the goal is to get a feel for race effort while paying attention to how you’re feeling as the workout progresses, terrain changes, etc. The last two pickups should be the most challenging and require all your focus to maintain the a hard effort from start to finish.

Why halftime recovery?

Halftime recovery, or a 2:1 work-to-rest ratio, is long enough to allow you to recover some between pickups, but short enough that it forces you to carry an increasing amount of fatigue into the next pickup, meaning the workout gets more challenging as it goes on.

How do I warm up?

Keep it simple: Jog for 15-20 minutes and then do 6-8 strides before beginning your 5-minute pickups. Cool down with 15-20 minutes of easy jogging.

Where should I do this workout?

Cross-country runners and ultra-distance athletes should do this workout on grass, dirt or trails to mimic the environments where their races will be held, while marathoners and other road racers should stick primarily to the asphalt. Of course, there’s no harm in off-road racers occasionally hitting the roads for this workout or road racers taking their fartlek to the trails from time to time, but in general it’s good practice to try and replicate the terrain you’ll compete on, especially as you get closer to your target races for the season.