Swedish for speedplay, a fartlek is a run of variable pace, and is one of the easiest ways to incorporate speedwork into your training. Instead of a set interval workout on the track, fartleks are loosely structured and can be done on the road or trail.
Start off with 10 minutes of easy jogging. Once you’re warmed up, pick a landmark about 200m away (or however far you want) and run towards it at a fast but controlled pace. Once you reach your landmark, slow back to a comfortable pace, or jog until your breathing returns to normal and you’re ready to make another hard effort. Repeat as many times as you feel like, then cool down with 10 minutes of easy running.
The strength of fartlek training is its adaptability. Do it in any manner you see fit. You can do a series of 100m sprints interspersed with recovery-pace running, or mix it up with a bunch of 600m or 800m sections at your 5K pace, or just simply sprint to the end of the block. Whatever you choose, you can’t go wrong with fartlek training.