What it is
Interval training alternates hard efforts with recovery jogs, repeated for a set number of reps. Run hard for 800 meters, jog for 400, do it again — that's an interval session.
The reps are typically anywhere from 400 meters to a mile, run at around 5k effort, with the recovery jog long enough to let you repeat the effort but short enough that you never fully recover. The structure is what makes it work: by breaking the hard running into pieces, you can accumulate far more time at a high intensity than you could in one continuous go.
Why it works
Intervals attack the parts of running that steady effort leaves alone.
At 5k effort your cardiovascular system is working near its ceiling, which is the stimulus that raises maximum oxygen uptake — how much oxygen you can actually deliver and use per minute. Continuous running at that intensity would last a few minutes at best. Broken into reps with recovery, you might accumulate 20 minutes of it in a session.
There's a mechanical benefit too. Running fast recruits muscle fibers that easy running never touches, and it forces a quicker, more efficient stride. Runners who never run fast get slower at running fast, independent of their fitness.
How to pace it
- The talk test. Not applicable — you're breathing too hard to talk. That's the point.
- Effort. 8–9 out of 10 by the end of each rep.
- Heart rate. Near maximum, 90–100%, by the last part of each rep.
- Race-pace shorthand. Roughly 5k pace for most rep lengths.
The crucial rule is that the set should be even. Your last rep should be within a couple of seconds of your first. If rep one is your fastest by a wide margin, you started too hard and the rest of the session is damage control.
Recovery between reps
Jog it, don't stand. Active recovery keeps blood moving and makes the next rep achievable.
As a starting point, make the recovery roughly half the duration of the rep for shorter reps and up to equal for longer ones. A 400m rep might get 200m of jogging; an 800m rep might get 400m; a mile rep might get a full 3–4 minutes.
A sample session
15 minutes easy warm-up, 6 × 800 meters at 5k effort with 400 meters of jogging between, 10 minutes easy cool-down.
If this is your first interval session, cut it to 4 × 800. You will feel like you could have done more, and that is the correct way to finish your first one. Add a rep every couple of weeks.
No track? Use time instead of distance — 6 × 3 minutes hard with 90 seconds of jogging works on any road or path.
Where it fits in your week
Once a week during a build phase, twice at absolute most and only for experienced runners. Never two hard sessions on consecutive days.
Have a real aerobic base first. Intervals layered on top of insufficient easy mileage is the most reliable way to get injured, because the speed arrives before the tendons are ready for it.
Common mistakes
- Running the first rep far faster than the last. An even set is a well-judged set. A descending one means you guessed your pace wrong at the start.
- Cutting the recovery short to "make it harder". Short recovery lowers the quality of the reps, which is where the benefit actually lives. If you want more stimulus, add a rep.
- Doing intervals more than twice a week. Two hard sessions is the practical ceiling for most runners, and one is enough for many.
Track it in Kamee
Track the session with GPS and let auto-pause handle the standing around at either end. The valuable part is afterwards: pull up your splits and look at the shape of the set. Flat is what you want. A staircase down means the opening rep set a pace you couldn't hold, and the fix next time is to start the first rep feeling slightly too easy.