The word Fartlek is Swedish for "speed play," and a Fartlek workout, typically performed outdoors, involves intervals of running at different speeds throughout the duration of your workout.
Improving your running performance will require the use of several different running techniques, one of which includes incorporating speed workouts like Fartlek training into your regular routine.
Fartlek workouts can vary in distance and pace depending on your goals and training program. It’s a technique most commonly used by intermediate and advanced runners aiming to increase their speed and aerobic capacity, but beginner runners can also benefit from performing simple Fartlek workouts too.
For example, a short Fartlek workout might look like something like this:
1-2 miles steady state running at warm-up pace
1-2 miles alternating between easy effort running and sprints, increasing your speed to a faster pace for an undesignated amount of time (to the next traffic light, tree or any other object in the near distance)
1 mile warm-down at recovery pace
Speed intervals should vary throughout the workout. The main idea is to run freely and alternate between a fast and moderate recovery pace without having to consult a watch or follow any sort of specific workout plan.