Most runners train at one pace: comfortable. Interval training breaks that habit. By alternating short stretches of hard effort with periods of easy jogging or walking, you teach your body to handle speeds it could never hold continuously – and over time, your comfortable pace quietly gets faster.
Why intervals work
Running hard for a few minutes pushes your heart, lungs and leg muscles close to their limit. The recovery in between lets you repeat that quality effort several times in one session, so you collect far more minutes at high intensity than a single all-out run would allow. The result is a stronger heart, better oxygen delivery and a more efficient stride. The same principle applies to cycling, swimming and rowing.
Three sessions to start with
Classic 400s: after a ten-minute easy warm-up, run hard for 400 metres (or 90 seconds), then jog for two minutes. Repeat six times. Pyramid: one, two, three, two and one minutes hard, with equal easy jogging between. Fartlek, the gentlest entry: during a normal run, pick a lamppost or tree in the distance and run hard until you reach it, then ease off until you feel ready again. No stopwatch required.
How hard is hard?
Hard means a pace you could hold for roughly ten minutes if you had to – controlled discomfort, not an all-out sprint. You should finish the last repetition feeling you could have done one more. If your form falls apart or the pace of the repetitions drops sharply, the session is over, whatever the plan said.
Keep it in proportion
One interval session per week is enough for beginners; experienced runners rarely need more than two. Everything else stays easy – the mix of mostly relaxed running with small doses of intensity is what drives progress. Skip intervals when you are ill, sore or returning from injury, and give yourself at least one easy day afterwards.
Warming up and cooling down
Intervals ask more of your muscles and tendons than steady running, so never start them cold. Ten minutes of easy jogging followed by a few strides – short, relaxed accelerations of about twenty seconds – prepares your legs for the first hard repetition. Afterwards, jog easily for five to ten minutes rather than stopping abruptly; it helps your heart rate settle and makes the next day's run feel considerably less wooden.
Common mistakes to avoid
The classic error is running the first repetition far too fast, then fading through the session. Aim for the same pace on the last repetition as the first – if anything, finish quickest. Other traps: doing intervals on consecutive days, treating the recovery jog as another race, and adding intensity in the same week you increase your total distance. Change one thing at a time and your body will keep up.
Tracking progress
Progress shows up in small ways first: the same repetitions feel smoother, your recovery jog gets quicker, or your heart rate drops faster between efforts. Every few weeks, repeat an identical session and compare how it felt rather than chasing numbers every time. Faster race times follow with a delay of several weeks – intervals are an investment, not a same-day purchase.
Try our running pace calculator to work out sensible target paces for your repetitions.
