Interval Training for Runners: What It Does and How to Do It

Interval training has a reputation as THE workout that makes you improve. Coaching sites hand you sample sessions and ratios, but rarely a study.

Published research says something more nuanced, and more useful: intervals work, continuous running works too, and your body does not respond like your training partner's.

What exactly is interval training?

Interval training alternates fast efforts with slower recovery periods (jogging or walking). Instead of running 30 minutes at a steady pace, you might run 6 repeats of 3 minutes fast, with 2 minutes of jogging between each one.

A workout can be adjusted in many ways: the length and intensity of the effort, the recovery, the number of repeats. Two sessions both called "intervals" may have almost nothing in common.

What it's for: what the studies say

Intervals mainly build your VO2max, the maximum amount of oxygen your body can use during exercise. The higher it is, the longer you can hold a fast pace.

The Milanović meta-analysis (2015) pooled 28 controlled studies with 723 healthy adults aged 18 to 45. Interval training and continuous endurance training both significantly improved VO2max. In direct comparisons, intervals kept a small edge: about 1.2 mL/kg/min more, with an uncertainty margin of 0.9.

So intervals do add real value, but the gains are measured in a few percent. That number comes from well-trained athletes. Do not treat it as a promise for your own race time.

The "80/20" rule: what it means (and what it doesn't)

You have probably read that you should do 80% of your workouts easy and 20% hard. The idea comes from Seiler's study (2010) on national and international-level endurance athletes. About 80% of their workouts were low intensity, and 20% included threshold or interval work. For 10 to 14 sessions per week, that works out to 2 to 3 hard workouts.

Two details matter. The percentage applies to workouts, not to time spent running. And it describes elite athletes, who train far more than you do.

Is this split the best one? A 2014 trial (Stöggl and Sperlich) said yes for polarized training: lots of easy running and a little very hard work. But the Rosenblat meta-analysis (2025), covering athletes with VO2max values from 46.6 to 68.3 mL/kg/min, found no significant difference between polarized training and other distributions, either for VO2max or time-trial performance. The 80/20 split is a benchmark from elite sport, not a proven rule.

Not everyone responds the same way

In the Bonafiglia study (2016), participants completed 3 weeks of endurance training followed by 3 weeks of sprint interval training (very short, maximal efforts), or the reverse. The workouts suggested below are a different format, so do not expect the same results. With both methods, some "non-responders" existed for VO2max, lactate threshold, or heart rate at moderate effort. However, everyone improved on at least one measure with each method.

The response is personal, and it depends on what you measure. If you do not gain VO2max, you may gain lactate threshold or heart rate at moderate effort instead. That is why it helps to track your data: pace on the same route, heart rate at the same pace, and how it feels.

Setting your paces and heart rate

To set your intervals, use two reference points. First, your MAS: the fastest speed you can hold for a few minutes. The calculator gives you your MAS, then interval paces based on it.

Next, your heart rate. The best-known formula (220 minus your age) is only an estimate. The Tanaka formula (2001), from a meta-analysis, gives 208 − 0.7 × age: at 40, that is 208 − 28 = 180 bpm. It is a population equation closely tied to age. It gives you a rough order of magnitude, not your personal maximum heart rate. Do not build precise zones to the single beat from it.

Your main guide is still how you feel: hard, but sustainable through the last repeat. If you have to slow down clearly by the fourth of six repeats, you started too fast.

What you can do in your next workout

The studies show that intervals help you improve. The sessions below are field examples, not formats compared in trials. This assumes you already run regularly. If you have pain or are returning from an injury, skip intervals and talk to a doctor first.

• Do one hard workout per week and keep the rest of your runs easy.
• Pick a simple format. For example, 10 repeats of 30 seconds fast with 30 seconds of jogging, or 6 repeats of 3 minutes with 2 minutes of jogging, after 10 to 15 minutes of easy warm-up running.
• Aim for consistency, not a personal record: the last repeat should look like the first.
• Space out your hard sessions: leave at least one easy run or a rest day between them.
• Track your progress by repeating the same workout every 3 or 4 weeks.

For where intervals fit into a full week, read Improve Your Running With 3 Workouts a Week.

• ✓I have written down my workout format (number of repeats, duration, recovery) before I leave.
• ✓My other runs this week are at an easy pace.

Since everyone responds differently, ELYO reads your workouts from your watch and compares them over time: pace, heart rate at the same pace, and consistency. You can see your own response to intervals, and your plan adjusts to it.

Written with the help of AI.