Interval training for runners

If easy running builds the engine and tempo runs raise the redline, intervals are what teach the engine to rev. They’re the most potent speed tool in running — and the one most likely to bury you if you treat every session like a race. Here’s how to use them well.

What interval training is

An interval session is short bursts of fast running separated by recovery — jogging or walking — repeated several times. The recovery is the whole trick: by resting between efforts, you accumulate far more time at high intensity than you could in one continuous hard run. A classic example: 6 × 400 metres fast, with a 200-metre jog between each. Six sharp efforts, stitched together by rest into one potent workout.

Intervals push your VO2 max — the ceiling on how much oxygen your body can use — and sharpen your legs and turnover in a way steady running never will. For 5K and 10K runners especially, they’re where a lot of the speed comes from.

Interval vs tempo vs fartlek

These three get muddled constantly:

• Intervals — hard efforts with full-ish recovery between them. Fast, then rest, repeated. Trains speed and VO2 max.
• Tempo — one sustained “comfortably hard” effort, no rest, at around threshold. Trains the pace you can hold. More here.
• Fartlek — Swedish for “speed play”: unstructured surges by feel during an otherwise easy run. Intervals without the stopwatch. A relaxed way in.

A simple session to start with

If you’re new to speed work, don’t start with a brutal track session. Try this after an easy warm-up: 6 × 1 minute at a hard-but-controlled effort, with 2 minutes of easy jogging between each, then an easy cool-down. Note that the effort is “hard but controlled,” not all-out — you should finish the last rep looking like the first, not staggering. Get the required paces for a more structured session from a pace calculator if you want numbers, but effort is the honest guide when you’re learning.

The mistake: racing every rep

The point of intervals is repeatability. If your first rep is so fast you’re falling apart by the fourth, you’ve done a bad time trial, not a workout. Controlled speed you can hold across every rep beats heroic speed you can hold for two — you’ll adapt more and recover faster. Leave a little in the tank on each one.

When not to do one

Intervals are the highest-stress running you’ll do, which makes them the most sensitive to how recovered you are. Show up to a hard session on four hours’ sleep and a resting heart rate five beats high, and you’ll hit slower paces, get less benefit, and dig a deep hole — the classic way a keen runner breaks their own plan. A hard day belongs on a day your body can absorb it, sandwiched by easy days on either side. The single most useful question before a speed session is whether today is actually the day for it — and sometimes it isn’t.

That judgement, made each morning from your sleep, heart rate, and recent load, is exactly what Liftrun is for: it schedules your hard sessions and then tells you when your body’s ready to nail one — and when the honest move is to run it tomorrow. Sharp legs come from good intervals, and good intervals come from doing them fresh.

Training guidance, not medical advice. Ease into speed work gradually and see a professional if pain persists.