This features formal fast-slow work and involves variable factors:
- the distance of the run
- the number of repeats of the run
- the speed of the run
- the duration of recovery after each run
- the type of activity during the recovery
An example would be: 400 metres x 10 @ 70 seconds each with a 90 second recovery between each, during which the athlete jogs 200 metres.
The session is normally performed on a running track, but not necessarily so.
This is a refinement of interval training and involves running a pre-determined distance a specified number of times with complete rest after each. it generally incorporates longer distances than interval training, such as 800-2000 metres.
An example would be 5 x 1000 metres with 6 minutes recovery.
This features informal fast-slow training and was popularized by the former national coach of Sweden, Gosta Holmer. The word means 'speed play' and there are infinite varieties of fartlek sessions. These are normally carried out on natural surfaces such as grass or forest paths and timing is not normally carried out.
An example would be: 10-15 minutes easy running as warm-up; brisk running for about 600 metres; jogging for 2 minutes or so; run hard up a nearby hill; easy running to a flat section; 6 x 100 metres with jog back; easy running for 10 minutes; hard running to a landmark some 1000-1500 metres in the distance; walking for 3 minutes; flat out sprints between landmarks such as trees over a shortish distance with jog recoveries of your choice etc.. etc..
As you can see, there is great variety in fartlek and the session is totally free and unplanned. Carried out properly, it can be extremely demanding.
The types of training above should result in your distance runs feeling that bit easier.