What Is The Norwegian 4x4 Workout? The Science-Backed Cardio Everyone Is Talking About

The Norwegian 4x4 workout is having a moment. It's all over TikTok, runners swear by it and longevity experts keep bringing it up whenever the conversation turns to VO₂ max.

But unlike plenty of fitness trends that come and go, this one has decades of research behind it.

What is the Norwegian 4x4 method?

The Norwegian 4x4 workout is a form of high-intensity interval training (HIIT) developed by researchers at the Norwegian University of Science and Technology (NTNU). They investigated the most effective ways to improve aerobic fitness and heart health and found that repeated blocks of exercise at around 85-95% of your maximum heart rate were among the most effective ways to improve VO₂ max compared with more moderate-intensity continuous training.

The workout follows a simple formula:

• Warm up for 5-10 minutes

• Work hard for 4 minutes

• Recover for 3 minutes

• Repeat the hard and easy intervals four times

• Cool down for 5-10 minutes

In total, it takes around 40 minutes, and you can do it running, cycling, rowing, swimming, on an elliptical or even by walking uphill on a treadmill. The type of cardio matters less than reaching the right effort during each four-minute interval.

The goal isn't to sprint. Instead, aim for an effort that feels hard but sustainable. You should be breathing too hard to hold a conversation, but still able to maintain the pace for the full four minutes. The three-minute recovery gives your heart rate just enough time to come down before you go again.

If you're new to VO₂ max, it's simply a measure of how much oxygen your body can use during exercise. It's one of the best indicators of cardiovascular fitness and has also been linked to long-term health and longevity.

Norwegian 4x4 workout at a glance

• Best for: Improving VO₂ max and cardiovascular fitness

• Workout length: Around 40 minutes

• Structure: 4 × 4-minute hard intervals with 3-minute recoveries

• Intensity: Around 85-95% of maximum heart rate (8-9/10 effort)

• Frequency: 1-2 sessions per week

• Equipment: Any cardio modality (running, cycling, rowing, swimming or walking uphill)

Why is everyone talking about it?

There are plenty of interval workouts out there, but few have been studied as extensively as the Norwegian 4x4.

One of the most influential studies, published by Jan Helgerud and colleagues in 2007, compared different aerobic training methods over eight weeks. Participants completing the 4×4 protocol improved their VO₂ max by significantly more than those performing moderate continuous exercise, while also seeing greater improvements in stroke volume (how much blood the heart pumps with each beat) and running economy.

Since then, researchers have continued studying the protocol in recreational exercisers, endurance athletes and people with cardiovascular disease. While the exact improvements vary depending on someone's starting fitness and training history, the overall finding has remained remarkably consistent: exercising at a high yet sustainable intensity is one of the most effective ways to improve your aerobic fitness.

A few important caveats

First, like a lot of health research, this study was done on forty men, so although we know HIIT is beneficial for women, the particular study people keep pointing to didn't include any.

That doesn't mean the findings don't apply to women. Plenty of research shows women can improve their cardiovascular fitness and VO₂ max through high-intensity interval training. But it's an important reminder that exercise science hasn't always included women equally, so we should be thoughtful about treating any single study as universal.

Your takeaway from this study also isn't that every cardio session should be high intensity to reap the benefits. Absolutely not. That's exhausting, unsustainable and a recipe for burnout. Lower-intensity training (like going for walks or training in zone 2) still plays a huge role in building endurance, supporting recovery and helping you train consistently. But adding one or two interval sessions like the Norwegian 4x4 each week can be an effective way to challenge your cardiovascular system.

How hard should the intervals feel?

This is where people often get it wrong.

The goal isn't to sprint for four minutes. That's not possible. And repeating that four times also wouldn't be possible if you've completely emptied the tank on round one. Instead, you want to work at an effort that feels hard but sustainable.

A good guide is:

• Around 85-90% of your maximum heart rate, if you use a heart rate monitor.

• Around 8 or 9 out of 10 on an effort scale.

• You should only be able to say a few words at a time, not hold a conversation.

Can beginners do the Norwegian 4x4?

Absolutely! Effort is relative. A beginner working at 8 out of 10 will obviously look different to an advanced athlete working at 8 out of 10, but it should feel equally challenging. If you're trying it out for the first time and it's feeling really tough, you also don't need to complete the entire workout straight away.

If four hard intervals feel pretty overwhelming, try:

• Completing two or three intervals instead of four.

• Shortening the work intervals to two or three minutes instead of four.

• Walking uphill instead of running.

• Reducing the intensity to 6 or 7 out of 10 while you build your confidence.

As your fitness improves, you can gradually build up to the full 4×4 session.

If you're new to vigorous exercise, have a heart condition or another medical condition, or you're returning after an injury, it's always a good idea to speak with your healthcare provider before starting high-intensity training.

How often should you do the Norwegian 4x4 workout?

One or two sessions each week is plenty.

Because these workouts are physically demanding, it's important to leave at least a day between sessions and balance them with easier cardio, strength training and recovery. More isn't always better. You're also likely to see better results and feel better in your body by mixing different training intensities across your week.

If you're following a program in the Sweat app, you could do this workout as one of your weekly cardio sessions.

Level up with interval training

The Norwegian 4x4 has earned its reputation. It's simple to remember, backed by decades of research and one of the most effective ways to improve your cardiovascular fitness in under 40 minutes.

You don't need every cardio session to be high intensity. In fact, you'll likely see the best results by mixing easier sessions with workouts like this. But if you're looking for an efficient, science-backed way to build your endurance, the Norwegian 4x4 is well worth trying. You might be surprised by what four minutes can do.