Fartlek

Definition: This is a form of interval training in which you alternate a work interval (e.g., sprinting) with a recovery interval (e.g., walking). The difference is that, in interval training, the intervals are measured. You might sprint for 30 seconds and then walk for 2 minutes. In fartlek training, the intervals aren't measured but are based on how the body feels. For example, if you were walking outside you might sprint as fast as you can until you can't go any further. Then you would walk until you feel fully recovered before sprinting again.