What interval pace trains
I pace is 3–5 km race pace, at 95–100% of VO2max. It is fast enough to stress the cardiovascular system and slow enough to repeat. A 22-minute 5K runner's I pace is around 4:15 per kilometre, which makes an 800 m rep about 3:24 — the kind of number you can check on a track without a spreadsheet.
Reps, not accumulations
The classic sets are 5–6 × 800 m, 4–5 × 1000 m, or 8–10 × 400 m, with 3 minutes of jogging between reps. Keep individual reps under five minutes: beyond that, the session becomes a threshold workout with extra fatigue. If the last rep is more than 3–4 seconds per kilometre slower than the first, stop the set.
Recovery is part of the session
The jog between reps lets you hit the target again. Shortening it turns the session into something harder but less specific. A useful rule is that recovery should be roughly 50–90% of the rep duration, and full enough that breathing is controlled before the next one starts.
Frequently Asked Questions
How fast should the recovery jog be?
Easy pace, not walking. The aim is to clear lactate and reset breathing, not to recover completely.
Can I do intervals on a treadmill?
Yes — set the speed and hold it. Treadmill intervals remove pacing error, which makes them useful for learning what the pace feels like.
How many interval sessions a week?
One. Two is possible for short-distance specialists but leaves little room for easy volume.
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