Key takeaways
- Intervals alternate hard, faster efforts with easier running or rest to recover, repeated for reps.
- They let you accumulate time at high intensity that continuous running can't.
- They build speed, VO2 max (aerobic power), running economy, and high-effort endurance.
- A workout is defined by the work (duration/intensity), the recovery, and the number of reps.
What intervals are
Intervals (interval training) are a workout method that alternates periods of hard, faster running with periods of easier running or rest to recover, repeated for several reps. The structure lets you do more fast running than you could in one continuous hard effort.
Why they help
Intervals let you accumulate time at high intensities — faster paces, higher heart rates — that you couldn’t sustain continuously, with recovery periods allowing more total fast running. This builds VO2 max (aerobic power), speed, running economy, and the ability to tolerate and sustain hard efforts — complementing the aerobic base from easy and long runs.
After warming up, a trail runner does 6 × 3 minutes hard uphill with 2-minute easy jog-down recoveries — six tough efforts that, broken up by recovery, total far more quality fast running than they could manage in one continuous hard push.
How they’re structured
By three variables: the work interval (how long/hard each effort is), the recovery (how long/easy the rest is), and the number of reps. Shorter, faster intervals with full recovery target speed and VO2 max; longer intervals with short recovery build sustained high-end endurance. They’re a more structured cousin of the playful fartlek and the sustained tempo run — done after a warm-up and balanced with easy days.
The bottom line
Intervals alternate hard, faster efforts with easier recovery, repeated for reps — letting you accumulate high-intensity running that builds speed, VO2 max, running economy, and high-effort endurance. Defined by the work, the recovery, and the number of reps, interval workouts are a cornerstone of structured training, complementing the aerobic base from easy and long runs. Warm up first and balance them with easy days.
Frequently asked questions
What are intervals in running?
Intervals (interval training) are a workout method where you alternate hard, faster running efforts with periods of easier running or rest to recover, repeating the cycle for a set number of reps. For example, running hard for a few minutes, jogging easily to recover, and repeating several times. The structure lets you do more fast running than you could in one continuous hard effort.
Why do interval workouts help?
Because they let you accumulate time at high intensities (faster paces, higher heart rates) that you couldn't sustain continuously, with the recovery periods allowing you to complete more total fast running. This stimulus improves VO2 max (your aerobic power), speed, running economy (efficiency), and your ability to tolerate and sustain hard efforts — adaptations that make you faster and fitter, complementing the aerobic base built by easy and long runs.
How are interval workouts structured?
By three main variables: the work interval (how long and how hard each fast effort is — e.g., 400m, 3 minutes, at a certain pace or effort), the recovery (how long and how easy the rest between efforts is), and the number of reps (and sometimes sets). Shorter, faster intervals with fuller recovery target speed and VO2 max; longer intervals with shorter recovery build sustained high-end endurance. Workouts are typically done after a warm-up and balanced with easy running on other days.
Sources
- Interval & speed training — American Council on Exercise
- Endurance training — Road Runners Club of America