What is the difference between interval training and HIIT?

HIIT (high-intensity interval training) is a type of interval training where the hard bouts are near maximal, at 85 to 95 percent of max heart rate. All HIIT is interval training, but not all interval training is high intensity. Some interval workouts use moderate efforts with longer or equal recoveries, which are still intervals but not HIIT.

What are the benefits of interval training?

Interval training raises your VO2 max faster than steady-state exercise, improves cardiovascular fitness in less time, burns significant calories, and can be adapted to any mode or fitness level. Higher VO2 max is also one of the strongest predictors of long-term health, so intervals do more than improve performance.

How do I start interval training as a beginner?

Begin with short, manageable intervals: after a 10-minute warm-up, alternate 30 seconds of moderately hard effort with 60 to 90 seconds of easy recovery, for 6 to 8 rounds, twice a week. As it gets easier, add rounds or shorten the recovery. Build the habit before chasing intensity, and keep at least 48 hours between hard sessions.

How often should I do interval training?

Two to three interval sessions per week is the sweet spot for most people, on non-consecutive days, with easy aerobic work or rest in between. Fitness gains come from intensity, not volume, so more than three hard sessions a week raises injury and burnout risk without extra benefit.

What Is Interval Training? Benefits, Types, and How to Start

Q: What is interval training?

Interval training is a method of exercise that alternates periods of hard effort with periods of easier recovery, repeated for a set number of rounds. The hard bouts push your heart rate up and drive fitness adaptations; the recoveries let you do more hard work than one continuous effort would allow. It can be done running, cycling, rowing, swimming, or with bodyweight exercises.

By Cristian Serb · Updated September 1, 2026

A runner accelerating into a hard interval on a track

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Interval training is a method of exercise that alternates hard efforts with easier recovery periods, repeated for a set number of rounds. Because the recoveries let you accumulate more hard work than one continuous effort would, it is the most time-efficient way to raise your fitness, especially your VO2 max. It works running, cycling, rowing, swimming, or with bodyweight moves, at any level.

Interval training is the single most effective structure for improving cardiovascular fitness, and it is simpler than it sounds. This guide explains what it is, the main types, the science-backed benefits, and how to start.

What Is Interval Training?

Interval training means alternating two kinds of effort:

Work: a hard bout, anywhere from 15 seconds to several minutes, that raises your heart rate and challenges your aerobic system.
Recovery: an easier period, from a few seconds to a few minutes, that lets you partly recover before the next hard bout.

You repeat that cycle for a set number of rounds. The genius of intervals is accumulation: by breaking hard work into repeated bouts with recovery, you spend far more total time at a high intensity than you could in one continuous effort, and time near your maximum is what drives fitness gains.

Types of Interval Training

Intervals come in several forms, defined by the length and intensity of the work and rest:

HIIT (high-intensity interval training): hard bouts near your maximum, at 85 to 95 percent of max heart rate. The umbrella term for the most intense intervals.
Tabata: 20 seconds all-out, 10 seconds rest, 8 rounds. Four minutes, extremely hard.
30/30 intervals: 30 seconds hard, 30 seconds easy. An accessible, sustainable format.
Norwegian 4x4: four 4-minute efforts at 90 to 95 percent of max heart rate with 3-minute recoveries. The most studied protocol for raising VO2 max.
Fartlek: unstructured "speed play" where you vary your pace by feel, useful for runners.

All of these are interval training; they differ in how hard and how long the bouts are.

The Benefits of Interval Training

Interval training is one of the most researched forms of exercise, and the benefits are consistent:

Raises VO2 max faster. A meta-analysis found intervals improve VO2 max more than steady-state training (Milanovic et al., 2015). VO2 max is the best single measure of cardiovascular endurance.
Saves time. Because intensity does the work, a 20 to 40 minute interval session delivers what a much longer easy workout would.
Improves health and longevity. Higher fitness is one of the strongest predictors of lower all-cause mortality (Mandsager et al., 2018).
Adapts to anything. Running, cycling, rowing, swimming, or bodyweight. The intensity matters more than the mode.

How to Start Interval Training

You do not need to start with all-out efforts. Build up:

Warm up for 10 minutes of easy movement.
Do 6 to 8 rounds of 30 seconds moderately hard, then 60 to 90 seconds easy.
Cool down for 5 minutes.
Repeat twice a week, adding rounds or shortening recovery as it gets easier.

Keep at least 48 hours between hard sessions, and build a base of easy aerobic work on the other days. Once you are comfortable, progress to formats like 30/30 and the Norwegian 4x4. For a full beginner path, see our interval training for beginners guide.

The Easiest Way to Run Intervals

The hardest part of interval training is the timing: you do not want to watch a clock mid-effort. PEAKVO2 runs the intervals for you on iPhone and Apple Watch, with full-screen color-coded phases, automatic transitions, a haptic tap at each switch, and your target heart rate zone for every phase. Pick a protocol, press start, and just train.

Run guided intervals with PEAKVO2

The Norwegian 4x4, Tabata, and 30/30 built in, on iPhone and Apple Watch, with automatic phases, a haptic tap at every switch, and heart rate zones. No stopwatch, no counting. Three workouts free.

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References

Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med. 2015;45(10):1469-1481. PubMed
Mandsager K, Harb S, Cremer P, et al. Association of cardiorespiratory fitness with long-term mortality. JAMA Netw Open. 2018;1(6):e183605. PubMed

Cristian Serb

I'm the developer of PEAKVO2. I built it because I was doing the Norwegian 4x4 myself and wanted the timing handled on my wrist so I could just train. I took my own VO2 max from about 41 to 51 with it. PEAKVO2 on the App Store.