Runners who purposely alternate between fast and slow while training are participating in which kind of exercise?
And the answer: fartlek.
Coming from the Swedish word that means "speed play," a fartlek is when the runner changes between fast sprints and easy jogs, all in the same run. The goal is to mix things up and keep training from getting too boring.
Oftentimes, doing your run training at the same pace will result in a performance plateau. Interestingly, the key seems to lie in easy running, rather than intense repetitions of timed trials. Fartlek training is a form of exercise that incorporates variety and freestyle into the more universally practiced interval training.
In fartlek training, runners will change their pace based on natural environment. Most fartlek runners will begin their workout without a strict or specific plan for their run, and will base their relative speed on landmarks around them. For example, beginners in fartlek training are recommended to pick a nearby landmark (say, a building or lamp post), and run at their faster 5k pace until reaching that point. Then, the runner can drop to a slower, sustainable pace more akin to that of a marathon. This can continue for as long as desired, though beginner fartlek sessions should be at least 40 minutes to allow for proper warm up and cool down.
Fartlek training can also be done with music as well. Some runners choose slower, more relaxed songs that allow them to slow their pace, followed by more upbeat songs to help inspire a 5k pace.
To learn more about fartlek training and its benefits, check out the video below.