Last updated: 3 October 2026
Reviewed by Jordan Morley, FA Level 2 Football Coach
Interval training alternates harder efforts with recovery periods, allowing more total time at high intensity than continuous effort would permit. Variations include HIIT (maximal efforts), threshold intervals (sustained hard efforts at lactate threshold), and fartlek (unstructured speed play). Intervals develop VO2 max, lactate threshold and speed more effectively than steady-state training alone. The work:rest ratio and interval length are manipulated to target specific adaptations — short intervals for VO2 max, longer ones for threshold.
- Alternates hard efforts with recovery
- More total time at high intensity
- Develops VO2 max, threshold and speed
- Work:rest ratio targets specific adaptations
In practice
Structured interval training alternates defined hard efforts with defined recovery periods, letting an athlete accumulate far more total time at a high intensity than a single continuous effort would allow — a runner who can only sustain 5k pace for 3 minutes continuously might complete six separate 3-minute reps at that same pace with short recoveries, delivering a much larger training stimulus.
FAQ
What's the difference between interval training and fartlek?
Interval training uses precisely defined work and rest periods (distance, time or pace), while fartlek is a more free-form, feel-based mix of faster and slower running within a continuous run.
How much rest should intervals include?
It depends on the training goal — shorter rest relative to work duration targets aerobic/threshold adaptations, while longer, fuller recovery between reps suits developing top-end speed or anaerobic power.