Interval training
Hard repeats with real recovery between them — what they develop, and why the recovery is part of the session rather than a gap in it.
- Hard, repeatable efforts — the last repeat should look like the first.
- The recovery is part of the session. Cutting it short changes what the workout does.
- Total hard running of fifteen to twenty-five minutes is a common working range.
- If the last repeat is much slower than the first, the session was pitched too hard.
What it is for
Intervals develop the top end: how efficiently you run at speed, and how much oxygen you can actually use. Running fast repeatedly also improves running economy — you get quicker at a given effort partly because the movement itself becomes cheaper.
They are the sharpening session. They work when the base underneath them is already there, and they disappoint when it is not.
How it should feel
- During a repeat: hard, controlled, unmistakably work. Talking is out.
- At the end of a repeat: you want it to stop, and you could have managed a little more.
- During recovery: breathing comes back down enough that the next repeat feels possible.
- At the end of the session: tired, not emptied. You should be able to run easy tomorrow.
The single most useful signal is consistency. The last repeat should look much like the first. A session that degrades sharply was pitched wrong, however impressive the first two felt.
How much is enough
Fifteen to twenty-five minutes of total hard running in a session, once a week during a block that calls for it. That range covers a lot of ordinary training and is not a requirement — shorter repeats at higher intensity and longer ones at lower both sit inside it differently.
| Session | Recovery | Total hard | Develops |
|---|---|---|---|
| 6 × 400 m | 90 s easy | ~10 min | Speed, economy |
| 5 × 3 min | 2 min easy | 15 min | Aerobic power |
| 4 × 5 min | 2–3 min easy | 20 min | Sustainable speed |
| 3 × 8 min | 3 min easy | 24 min | The bridge toward tempo |
Warm up properly — ten to fifteen minutes easy, then a few short strides. Cold intervals are where calf and hamstring problems come from.
What runners commonly get wrong
- Treating recovery as wasted time. It is what allows the next repeat to be run at quality. Cutting it turns a speed session into a fatigue session, which is a different workout with different effects.
- Starting too fast. Repeat one nearly always feels easy. Judge the session by whether repeat five is still on it.
- Doing them instead of building a base. Intervals sharpen what exists. Without consistent easy running underneath, they produce a brief improvement and then a wall.
- Adding them to a week that is already hard. Two hard sessions and a long run in one week is a lot for most runners, and it is the point at which the easy days quietly stop being easy.
Common questions
How fast should intervals be?
Fast enough that the effort is clearly hard, and controlled enough that the final repeat is close to the first. If repeat six is markedly slower than repeat one, the session was started too fast — which is more informative than any target pace.
How long should the recovery be?
Long enough to complete the next repeat at the same quality. For short repeats that is often roughly equal to the work; for longer ones it is usually less than the work. Shortening it makes a different, harder session — sometimes deliberately, but know which one you are doing.
Do I need a track?
No. A track makes distance-based repeats convenient, but time-based repeats on any flat, uninterrupted stretch work as well and are often easier to judge.