Interval Training Explained: How (and Why) to Train in Intervals

TL;DR — Interval training means alternating fast efforts with recovery periods. It's the number-one tool for developing your VO2max, running economy, and pure speed. There are several formats: short (30/30 or 200-400m), long (1000m), hills, tempo. A typical session always has three parts: warm-up, intervals with recovery, cool-down. One to two sessions a week is enough — most runners go too fast and too often. Easy running stays the base; intervals are the seasoning on top.

You've been running regularly for a while and you feel like you've hit a plateau? It's probably because the other half of the equation is missing: intensity. Interval training sounds scary — you picture torture sessions on a track — but it's actually one of the most effective ways to improve, as long as you dose it right. Here's the playbook, from why to how.

What is interval training?

Interval training means alternating phases of hard effort with phases of recovery. Instead of running 40 minutes at a constant pace, you string together fast portions separated by short active breaks.

The point is simple: running fast continuously over a long duration is impossible, but by breaking it up, you can accumulate far more time at high intensity than in one shot. You run fast, you recover, you go again — and in total, you work your engine at a level you could never sustain in a single block.

It's the natural complement to easy running: the base gives you the tank, intervals sharpen the blade.

Why it makes you faster

Interval training works on several levers at once.

First, it develops your VO2max, your ability to consume and use oxygen at high intensity. Think of it as your engine's displacement: the bigger it is, the more all your paces improve. To understand this concept in detail, our VO2max, heart rate zones and running paces guide is made for that.

Second, it improves your running economy: by running fast repeatedly, your stride becomes more efficient, more springy, better coordinated. You spend less energy at the same pace.

Third, it develops your pure speed and your tolerance for discomfort. Learning to run fast, mentally and physically, makes you more comfortable when you need to surge in a race or hold a demanding pace.

Types of interval training

Not all sessions are equal: each targets a different goal.

• Short intervals (30/30, 200-400m): brief, fast efforts followed by short recovery. The 30/30 — 30 seconds fast, 30 seconds slow — is a classic, ideal for working VO2max without exhausting yourself. Very accessible for those new to intensity.
• Long intervals (800-1000m): longer reps at a strong pace, with more generous recovery. More demanding mentally, it builds your ability to hold a fast pace over time.
• Hills: short, high-intensity climbs. Excellent for power and leg strengthening, with less jarring impact than the track. Recovery happens jogging back down easily.
• Tempo (threshold): a "comfortably hard" effort held longer (in blocks of several minutes), right at the border between ease and breathlessness. Ideal for longer distances like the half or marathon.

How to build a session

An interval session always has three parts, and the warm-up is non-negotiable.

1. The warm-up: 15 to 20 minutes of very easy jogging, followed by a few progressive accelerations (strides). Your body needs to be warm before the first fast effort — that's what protects your muscles and lets you run well.

2. The main set: your intervals, broken up by recoveries. Recovery can be active (very slow jog) or passive (walking), and its length depends on the format. On short sets like 30/30, recovery often equals the effort; on long ones, it's more generous. The golden rule: you should be able to hold the same pace across all reps. If you slow down noticeably at the end, you started too fast.

3. The cool-down: 10 minutes of very slow jogging to bring your body back down. It kick-starts recovery and limits heavy legs the next day.

How often, and the mistakes to avoid

This is where the whole balance plays out. One to two interval sessions a week, no more. Intervals are demanding: they need recovery to pay off. Doing too much opens the door to chronic fatigue and injury.

The most common mistakes:

• Running too fast: the goal isn't to finish in agony, but to hold the target pace across all reps. Too fast from the start and the session collapses.
• Doing it too often: three or four hard sessions a week won't make you stronger, just more tired. Respect the roughly 80% easy / 20% hard ratio — detailed in our zone 2 guide.
• Skipping the warm-up or cool-down: that's taking a pointless risk to save ten minutes.

Interval training suits all levels once you have a regular endurance base. Start with short, low-volume sessions, then progress patiently.

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FAQ

What exactly is interval training in running?

It's a training method that alternates phases of fast effort with phases of recovery. Rather than running at a constant pace, you string together intense reps separated by active or passive breaks. This lets you accumulate far more time at high intensity than you could hold in a single block.

Is interval training only for advanced runners?

No, it suits all levels once you have a regular endurance base. Beginners simply start with short, low-volume formats like the 30/30. The key is dosing: you build the aerobic base first with easy runs, then gradually add one intensity session per week.

How fast should I run the intervals?

At a pace you can hold identically across all reps, not flat out from the start. If you slow down noticeably on the last reps, you started too fast. The target pace depends on the format: the shorter the reps, the faster they are; the longer they are, the closer the pace gets to your race pace.

How many interval sessions per week?

One to two sessions a week is enough, never more. Interval training is demanding and needs recovery to pay off. Piling on hard sessions leads to chronic fatigue and injury, with no extra gain. Keep the rest of your runs easy, following the roughly 80% easy / 20% hard principle.

Do I need a track for interval training?

No, a track is handy for measuring distances but not essential. You can do time-based intervals (like 30/30) on any flat route, or hill sessions on a climb. A watch or a simple stopwatch is enough. The key is respecting the effort and recovery phases.

Intervals or easy runs: which makes you improve more?

Both are complementary and essential. Easy running builds your aerobic base and lets you absorb volume; intervals sharpen your VO2max, running economy, and speed. Without the base, intervals have nothing to stand on; without intensity, progress plateaus. Aim for balance, not one against the other.