Fartleks are similar to interval running sessions because there is speed work involved, but they can be less structured and often involve continuous running rather than resting breaks.
“A lot of interval sessions are structured in a way that they have a certain rep time or rep distance, and then you have a set recovery time within that,” says Moses.
An interval session on a running track could be 400m hard efforts, with a two minute rest in between, repeated six times.
“With a Fartlek run, the fun thing is that you have the license to play around with it,” says Moses. “That’s why I really like it as a concept for training. There is some element of repetition, but you can play around with the speed, terrain and recovery time and you are not aiming to put in the same effort with every repetition.”
Often the recovery periods during Fartlek training will be at an easy pace rather than standing still, known as active recovery. So even if you have run a hard rep you will keep running once it is complete, just at a much lower intensity.
“Interval sessions tend to have a lot more passive recovery, where people stand around letting their heart rate drop back down, whereas with a Fartlek you get that nice aerobic stimulus from that continuous effort,” says Moses.