4x4 High Intensity Intervals
Supported by the originators of the Norwegian Protocol
The 4x4 interval training method, also known as the Norwegian Protocol, is a simple but efficient way to improve your VO₂max. It includes four repetitions of intense breathing, separated by three-minute active breaks.
Warm-Up
Prepare the body and gradually increase intensity.
Intervals
Four minutes at a high but sustainable breathing threshold.
Active Breaks
Three minutes of active recovery so the next interval can be effective.
What is 4x4 interval training?
The 4x4 interval training method, also known as the Norwegian Protocol, is a simple but efficient way to improve your VO₂max and overall fitness. It involves four minutes of heavy-breathing, repeated four times, separated by three-minute active breaks.
The 4x4 interval method has been extensively researched and validated by experts like Professors Jan Hoff and Jan Helgerud, who are the founders of Myworkout and leading authorities on exercise physiology and medicine. They have published over 200 peer-reviewed articles on PubMed, consulted numerous elite athletes and teams, and applied their training principles to various clinical populations.
Benefits with 4x4 intervals
The 4x4 interval training method is considered the golden standard to increase your maximal oxygen consumption (VO₂max), which is the maximum amount of oxygen your body can use during exercise. Again, VO₂max is one of the strongest predictors of cardiovascular health and mortality, and longevity.
As we age, our VO₂max decreases by about 1% per year, which means that our physical capacity and health deteriorate over time. However, the 4x4 interval training method has shown remarkable anti-aging effects, improving both your VO₂max and your biological age. Biological age is a measure of how old your body is based on your health status, rather than your chronological age. By improving your VO₂max, you can reduce your biological age and improve your quality of life.
As featured in
4x4 interval protocol · scroll story
One session. Four repeated ideas.
Scroll through the workout. The protocol illustration stays visible and highlights the part of the session being explained.
Start the walkthrough1 Warmup
Build the engine before the hard work starts.
Start with a gradual warmup. The goal is to raise your breathing, loosen the body, and prepare the heart for the high-intensity intervals.
- +Begin calmly and let the intensity rise gradually.
- +Use this section to find rhythm, breathing, and movement quality.
2 High-intensity interval
Four minutes where the session matters most.
Each interval should be hard, but sustainable for the full four minutes. You should breathe heavily and feel challenged without sprinting or losing control. A rule of thumb is that you should be able to continue for another minute at this intensity when the active break starts.
- +Avoid starting too hard; the last minute should be demanding but possible.
- +The illustration highlights all four work blocks to show the repeated structure.
- +A 5% incline or more is recommended when walking/running
3 Active break
Recover, but keep moving.
Active breaks are crucial for removing lactic acid and preparing for the next interval. You must reduce your speed so that you can breathe and speak normally again. Make sure the intensity doesn't drop too low, as this will only make it harder for you to get your heart rate back up in the next interval.
- +Slow down until breathing becomes more controlled.
- +Use the break to prepare for the next four-minute interval.
4 Cooldown
Bring the system down gradually.
End with a cooldown after the final interval. Slow down gradually and assess whether you could perform another interval. If the answer is
- +Do not stop abruptly after the final high-intensity block.
- +Finish at an easy pace before ending the session.
Personalized training experience
The 4x4 interval training method is as efficient as it is adaptable. You only need 16 minutes of heavy breathing twice a week to increase your VO₂max and improve your biological age. You can perform the 4x4 intervals with any type of exercise that challenges your cardiovascular system, such as running, cycling, rowing, skiing, or using an elliptical.
- 16 minutes of heavy breathing
- Two sessions each week or more
Better effects with incline
When running uphill, the heart and breathing become the limiting factors rather than technique. That makes incline work especially effective for maximum oxygen uptake. With active breaks, you can keep going for longer, collect more minutes with a high heart rate, and make the session more effective. The mechanical load is also lower than running on flat ground, which matters if you train often or need a gentler option for your back and knees.
Now available on Kindle - get your own copy
Dive into the science, story, and practical tools behind the 4x4 method. In this book, Professors Jan Hoff and Jan Helgerud break down decades of research into training programs, testing, performance, and longevity tools. A perfect read for athletes, patients, and anyone curious about the method’s origins and impact. Get it on Kindle
Myworkout 4x4
The 4x4 method is one of the foundational pillars of our app, Myworkout 4x4, and it serves as a tool to optimize your quality of life and increase your health status with scientific accuracy.
Science-backed App Development
The Myworkout technology and its precision in measuring VO₂max and biological age comes from robust scientific research. The published study “Prediction of VO₂max from Submaximal Exercise using The Myworkout smartphone application: Myworkout GO” by Jan Helgerud, Atle Holme, and Jan Hoff demonstrated the app’s accuracy.
The conclusion found that Myworkout GO accurately calculates VO₂max and is a practical tool for health and risk stratification, with the potential to increase physical activity and improve exercise habits in the general population.
With the published study “Smartphone-Assisted High-Intensity Interval Training in Hypertension: Treatment Efficacy, Preference, Randomized-Controlled Trial” by Jan Helgerud, Jaume Mora, David Moran, and Josey Hoff, Myworkout 4x4 follows the same principle of frictionless, guided high-intensity training.
Accurate Health Assessments
The app estimates VO₂max and biological age by assessing your performance during a standard 4x4-minute high-intensity interval session. The test’s margin of error is 4.5%, which means it is very close to direct VO₂max measurement. The app also compares your VO₂max and biological age with the average values for your gender and age group, and shows how you can improve them over time. This approach is safer and more accessible than direct measurements, even for people with health concerns.
Unlocking Health with Gamification
When the app knows your VO₂max, it can understand when you are in the right intensity zone for four minutes of activation. We call this zone HIT (High Intensity Training).
The app gives you goal points for hitting the correct intensity during the intervals, based on your capacity and heart rate. You only need 30 HIT points per week to keep your streak, making it an achievable goal for everyone. The app also tracks progress, rewards achievements, and motivates you to stay consistent and keep challenging yourself.
By improving or maintaining capacity over time, you can move your physiological age closer to a much younger biological profile.
Application of science
For outdoor exercise, the app uses VO₂max in the background, GPS, and sensor data to estimate speed and incline. Indoors, on a treadmill, it uses the recorded incline and speed. For devices like rowing machines, bikes, and ellipticals, you can enter your data manually.
No exercise equipment is needed, just a smartphone. However, if you already use wearables, you can integrate them with the app.
Want to try 4x4 yourself?
Our app is the easiest way to get started with 4x4 training. It guides you through each interval, helps you stay consistent, and measures your fitness automatically.
