The definition of the Swedish word Fartlek is 'speed play' in English and it means running, cycling and swimming at different speeds.

　　What is fartlek running?

　　Using running as an example, fartleck involves no more than picking up speed when and wherever you feel like it on, say, an eight-mile run. There’s no structure and nor should there be. So if you feel like running flat out for 20secs, go for it.

　　Want to run at 80% of your heart rate max for 8mins? Fine. The distances run – and the recovery between efforts – are your choice. That could mean 20secs jogging or 20mins steady running. Any scenario is perfect in the world of fartlek.

　　When it was first introduced in Sweden in the 1940s, mile world record-holders Gunder Hägg and Arne Anderson used it to surge and jog as they felt appropriate in the forest. But you can spice things up (and toughen up mentally) by introducing a few rules.

　　How to fartlek train with others

　　You could choose to surge hard when, for example, you pass a red door, and keep that pace high until you see another one. That might result in a short 10sec burst or a longer 10min sustained effort. When you set off, you won’t know. Just as an opponent surges hard in a race, so fartlek can simulate that rival.

　　Personally, I love a fartlek session with three or four training partners. Each will take a turn setting the pace, but mustn’t say how far they’re surging for. Your job is to hang tough until the effort is finished.

　　It’s amazingly difficult to do, as well as creating a great session. Fartlek lends itself to any surface, any environment and any discipline, and really should be included in your training programme once a week.