Training

What Is Interval Training?

Published September 1, 2026 By SUBNONE

Alternating hard efforts with recovery periods. The four variables that define a session, three to start with, and why cutting the recovery short defeats the point.

Runners doing hill repetitions, one running up while another jogs back down

The short answer: interval training means alternating short bursts of hard running with periods of recovery. For example, six repetitions of 400 metres run fast, with 90 seconds of easy jogging between each. It builds speed, running efficiency and the ability to tolerate hard efforts.

The basic structure

Every interval session has four variables:

The work. How long or far you run hard — 400m, or 3 minutes, for instance.
The intensity. How hard you run it.
The recovery. How long you rest between, and whether you jog or walk it.
The repetitions. How many times you repeat it.

Change any of those and you change what the session trains. Longer reps with short recoveries build sustained speed; shorter reps with full recoveries build top-end speed.

Why the recovery matters

The recovery is what lets you run the hard portions genuinely hard. Without it you'd simply be running a tempo run.

This is worth internalising, because the instinct is to treat recovery as wasted time and cut it short. Doing that turns a sharp interval session into a mediocre continuous one — you end up running the reps slower and getting less from the session.

Recovery jogs should be slow. Genuinely slow. Walking is fine too.

Sessions worth starting with

Always with 10-15 minutes of easy jogging as a warm-up, and the same to cool down. This isn't optional for hard running.

Hill repeats. The best entry point. Run hard uphill for 45 seconds, jog down to recover, repeat 6-8 times. The gradient caps your speed, which substantially reduces injury risk compared with flat speed work.

Short reps. 6-8 × 400m at roughly 5K effort, with 90 seconds easy jogging between.

Time-based reps, useful if you're not near a track. 5 × 3 minutes hard with 2 minutes easy jogging between.

Any of these once a week is plenty.

How hard is hard?

For most sessions, around the effort you could sustain for a 5K race — not a sprint. You shouldn't be able to talk during the reps.

The key marker of a well-paced session is that the last rep is roughly as fast as the first. If rep six is significantly slower than rep one, you started too fast and got less out of the session, not more.

Beginners at interval work almost universally go too hard on the early reps. Deliberately holding back at the start is the skill.

When to start

After several months of consistent running, once you're comfortable running 40 minutes or so, and ideally after you've been doing tempo work for a while.

Intervals carry the highest injury risk of any session type, because they involve running fast, and running fast on unprepared legs is how people strain calves and hamstrings. The base comes first.

If you're newer than that, more easy running will improve you faster. See how to get faster at running.

Intervals versus tempo

Intervals are short, very hard, with recovery. Tempo is sustained and moderately hard. For 5K and longer, tempo work generally delivers more benefit for most runners. Intervals add sharpness on top of that.

Doing both in the same week is reasonable for experienced runners with a decent volume base. For most people, alternating them week to week is plenty.

How often

Once a week at most, alongside easy running the rest of the time. Two hard sessions a week is achievable for experienced runners with high volume; for everyone else it's the fast route to being permanently tired.

A note on injury risk

Because intervals involve running fast, they carry more injury risk than easy running. Warm up thoroughly, stop the session if something feels sharp rather than merely hard, and don't do them when you're already fatigued. Any pain that is sharp, localised, or worsens as you run is worth seeing a GP or physiotherapist about. General guidance, not medical advice.