Might be why the “fartlek” workout has been a fixture in running plans for decades. In Swedish it means speedplay and the original structure of the workout was

Might be why the “fartlek” workout has been a fixture in running plans for decades. In Swedish it means speedplay and the original structure of the workout was there is no structure. Start running, spot a landmark like a pole, run hard to it, jog until you see another one like a tree, run hard to it, and repeat. This research might suggest this type of activity let’s athletes run harder than they normally would. Nowadays many coaches prescribe timed intervals to structure the fatlek, so the original idea behind it has kinda been lost though. In fact, timed workouts actually have the opposite effect where athletes perform worse at the same rate of perceived effort than distance based workouts.