What interval training is and how to do it

A simple definition

Interval training is alternating stretches at a hard pace with stretches of recovery (jogging or walking). The idea is to accumulate more time at high intensity than would be possible continuously: running 5 × 1,000 m hard with a 2-minute jog between them is doable; running 5 km at the same pace without stopping is not.

Each session is defined by four variables: distance or time of each hard stretch, pace of the hard stretch, length and form of recovery, and number of repetitions. Changing any of them changes the stimulus — which is why "intervals" isn't one workout, but a family.

Why it works

At high intensities the body is forced to improve oxygen uptake and use (VO2max), tolerance to lactate accumulation and running economy — the energy spent to hold a pace. These are adaptations easy running alone doesn't produce, no matter how much volume you do.

Intervals also teach the brain to sustain discomfort for defined stretches, which makes a direct difference in racing: anyone who has run 6 × 800 m hard knows kilometer eight of a 10K is bearable.

Examples by goal

For a 5K: 8 × 400 m at 5K pace or slightly faster, with a 200 m jog. For a 10K: 5 or 6 × 1,000 m at 10K pace, with a 2-to-3-minute jog. For a half marathon: 4 × 2,000 m between 10K and half pace, with a 3-minute jog. For someone new to intensity: 6 × 1 minute hard with 2 minutes easy, inside a 30-minute run.

Always with a 10-to-15-minute jog warm-up (plus two or three strides) and a 10-minute cool-down. The warm-up isn't optional: it's what separates a productive workout from a muscle strain.

The mistakes that cancel out the workout

Running the first rep too fast. Intervals should be "controlled": the last reps at the same pace as the first, or even slightly faster. If you go from 4:00 to 4:40 per kilometer over the session, you went out too hard and trained fatigue, not speed.

Doing more than one a week as an amateur, or doing intervals the day after a long run. One hard workout a week (two, at most, in peak phase) is enough; the rest of the volume is easy. Intervals are the seasoning, not the meal.

How PaceOn helps

Every interval session in the plan comes with its structure explained step by step — warm-up, reps, recovery, cool-down — and with a pace range computed from your runs, not from a generic table. When you import the activity, the system compares the hard stretches with the target and comments on whether they came out too fast or nicely controlled.