Fartlek (Swedish for ‘speed play’) is a flexible, unstructured form of interval training where the runner varies pace spontaneously — surging to a landmark, easing off, then surging again. Developed in Sweden in the 1930s, it blends continuous and interval training, developing both aerobic and anaerobic systems while keeping training enjoyable and adaptable to terrain and feel. Unlike track intervals, fartlek has no fixed structure, making it mentally refreshing and easy to incorporate into any run.
Key points
- Swedish for ‘speed play’
- Unstructured, spontaneous pace variation
- Develops aerobic and anaerobic systems
- Flexible and mentally refreshing
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