Cardiorespiratory Fitness - Fartlek training

In Fartlek training, another type of CR training sometimes called speed play, the soldier varies the intensity (speed) of the running during the workout. Instead of running at a constant speed, he starts with very slow jogging. When ready, he runs hard for a few minutes until he feels the need to slow down. At this time he recovers by jogging at an easy pace. This process of alternating fast and recovery running (both of varying distances) gives the same results as interval training. However, neither the running nor recovery interval is timed, and the running is not done on a track. For these reasons, many runners prefer Fartlek training to interval training.