Swedish for "speed play", fartlek training is a form of interval training that is effective for your running speed and endurance. 

Fartlek training is becoming quite popular among runners. It involves speed work, yet is less rigorous than traditional interval training. Fartlek training also adds extra stress on your body system, which leads to faster speeds and improves your anaerobic stamina.

Key Benefits:

1. Engage different muscle fibres during various aspects of training. Slow-twitch muscle fibres during jogging and medium to fast-twitch muscle fibres during sprints
2. Not only will you improve your strength and endurance, but your potential top speed as well.
3. Improved lung compacity with the extra sprint load and the need to catch your breath
4. Improve your cardio capacity as well

Sample Workout:

1. 10-15 minute warmup at a comfortable jogging pace
2. Fartlek set: 1-minute fast pace, 2 minutes slow pace, 1-minute recovery
3. Repeat the fartlek set 3 to 4 times
4. 10-15 minute cool down