What is fartlek training?

• A. A structured interval protocol with predefined work and rest.
• B. A steady tempo run at race pace.
• C. A form of isometric training used for joint stability.
• D. A form of unstructured speed play mixing fast and slow periods to improve speed, endurance, and economy.

Answer: (D)

Fartlek training centers on speed play, mixing fast and slow running in a flexible, informal way. There’s no fixed structure—pace changes are based on how you feel, the terrain, or landmarks you choose. This variability challenges both the aerobic and anaerobic systems, helping to boost speed, endurance, and running economy because your body learns to adapt to changing demands. By contrast, a predefined interval workout uses exact work and rest intervals, a tempo run stays at a steady, near-threshold pace, and isometric training targets static holds for joint stability rather than pace. Fartlek’s strength lies in its spontaneous, adaptable approach to alternating effort, which translates into more versatile performance.