People who have a high VO2max—one measure of cardio fitness—tend to be healthier as they age, and may be able to expect a longer lifespan. With that in mind, some longevity influencers have been singing the praises of the “Norwegian 4x4” workout, which is targeted to improve your VO2max. So how do you do it? And is it really a magic bullet for fitness and longevity? Let's get into it.

What kind of workout is the Norwegian 4x4? 

I’ll give a step-by-step further down, but basically it’s a cardio workout (traditionally done while running) that features four-minute-long intervals. You do four of these hard four-minute intervals, hence the name 4x4. There is also a warmup at the beginning of the workout, a cooldown at the end, and a three-minute rest period between each interval.

If you’re a runner, you’ll recognize this as a classic VO2max interval workout. (Typically, VO2max intervals are done for three to five minutes, with a recovery time similar to, or slightly less than, the work time.) Couldn’t I just do any old VO2max interval workout? You might be asking. Yes, you can.

The Norwegian 4x4 is a good example of a VO2max interval workout, but it’s not the only one. Also, intervals like these that target your VO2max pace are not the only way to improve your VO2max. So the 4x4 isn’t unique or special, it’s just a simple protocol that’s easy to remember and has been tested on a wide variety of people, including elderly people with heart conditions. 

What benefits can I expect from the Norwegian 4x4 workout?

After doing this workout regularly (say, twice a week) for several weeks to months, you can expect an increase in your cardio fitness, including metrics like the “cardio fitness” or “VO2max” readings on your smartwatch. If you like to run races, you’ll notice you can run them a bit faster. It will be harder for you to get winded if you go for a hike or run around in the backyard with your kids. 

Your heart health will likely improve; this exercise fits right in with the exercise recommendations for heart health and general health. Cardio exercise in general, including intervals like these, tends to reduce people’s risk of heart disease, improves mental health, and more. Again: you can get similar results from other exercise, too. But 4x4 is one good option among many. 

How to do the Norwegian 4x4 Workout

The 4x4 gets its name because you are doing four repeats of a four-minute-long hard intervals. The authoritative source on this is the Cardiac Exercise Research Group at the Norwegian University of Science and Technology (NTNU), which has a video with researcher Anja Bye explaining how it works. Refer to that source for your follow-up questions, not podcasters or influencers who try to translate it into zones or modify the repeats or rest times. If you want to do the 4x4, do it right. (Then experiment with it on your own, if you choose.) 

The 4x4 was originally designed to be done while running, but the researchers say it’s OK to do it with other activities like “swimming, biking, or skiing.” (Forgive me if I don’t have skis at the ready.) Here’s the protocol: 

• Warm up with 10 minutes of moderate intensity jogging or brisk walking.

• First interval: 4 minutes at a hard pace. It may take 1-2 minutes for your heart rate to reach the target (85-95% of your tested max HR), and that’s OK. If you don’t have a heart rate monitor or you don’t know your true max, aim to work hard enough that you can’t talk in full sentences. Bye says “the intensity of the last minute should be high, but not so exhausting that you cannot complete it.” 

• Recovery: 3 minutes at a moderate pace, jogging or brisk walking. Aim to get back to 60-70% of your max heart rate. 

• Repeat the intervals until you have done four of them, in total.

• Cooldown: 5 minutes of moderate intensity again.

In total, that’s 40 minutes: 

• 10 minute warmup

• 4 minute hard interval

• 3 minute recovery

• 4 minute hard interval

• 3 minute recovery

• 4 minute hard interval

• 3 minute recovery

• 4 minute hard interval

• 5 minute cooldown

Note that it’s three minutes of recovery between hard intervals, not four. (People tend to misremember this part.) Also: don’t skip the warmup. It helps get your heart rate up so you’re ready for the first interval. 

How often should I do the Norwegian 4x4 workout? 

The NTNU recommends doing it twice each week, plus one longer cardio session where you exercise at a moderate pace only. They also recommend that if you’re exercising four times or more each week, that your interval sessions be half or less of your total training. That would generally still mean two 4x4 sessions per week, since you would be doing two to four sessions of some other type of exercise.

What heart rate zones should I be in? 

Trick question! This is not a zone-based workout. If you use a heart rate tracker, you have numeric targets:

• 85-95% of your tested max during the final 2-3 minutes of the 4 minute intervals

• 60-70% during the warmup, recovery, and cooldown periods.

That 85-95% range includes parts of zone 4 and 5, in most of the five-zone systems. The recovery heart rate may put you in zones 1 and/or 2, again, depending on how your watch sets it up. (As I keep saying, the zone boundaries vary by device.) 

If you’re using heart rate as a target, make sure you know your actual max heart rate. Don’t trust your device to calculate it; people are different and the default formula can easily be off by 10 beats or more. NTNU recommends using a modified version of the 4x4 to test your max. Begin the workout as above, but when you get to the third interval, run it all-out. The highest number you see on your watch during this test is the number you should use as your max. 

Is this a zone 5 workout? 

You’ll probably reach zone 5 at some point during the intervals, so in that sense, yes. But the point is not to hit zone 5, the point is to follow the protocol.

Is this a VO2max workout? 

Yes, this is a pretty classic set of VO2max intervals. That said, it’s not the only way to improve your VO2max! Good cardio fitness comes from training in a variety of ranges, including longer, slower workouts, and intervals of various lengths and intensities. All of this will ultimately improve your VO2max, and better yet, your cardio fitness in general. 

The idea of a VO2max workout comes from athletic training, where coaches will consider the different aspects of running performance and will program different types of workouts throughout the season to help their athletes improve their strong points and shore up weak points. “VO2max” intervals are part of that process. 

In a separate thread of logic, researchers who study heart health and longevity have found that VO2max is an aspect of fitness they can test in a consistent, repeatable way. People with better cardio fitness tend to be healthier and live longer, so you can correctly say that a VO2max is associated with health. But that’s not because you need to improve your VO2max relative to other aspects of fitness; it’s because improving your fitness will improve your health, and your VO2max will go up as a side effect.

Am I doing it right? 

I keep seeing Reddit posts from fans of various biohacking podcasts, asking whether they did their 4x4 workout right. Here’s a checklist: 

• Did you look up the protocol from its actual source on NTNU? Because some influencers don’t explain it correctly, or they mention it alongside other exercise protocols and it’s easy to get confused about what the protocol actually is.

• Did you do the warmup and cooldown? The warmup sets you up for a good first interval. If you start from complete rest, you’re wasting a lot of that first interval just on getting your heart up to speed.

• Did you do three-minute rests? Not four minutes. Three minutes. (Not that four-minute rests would be bad, but it’s not the 4x4 protocol.)

• Were you at 85-95% of your max heart rate during the last two minutes of each interval? It takes time for your heart rate to ramp up, but you should be hitting the target for at least the last half of each interval.

• Were you at 70% or less during most of the recovery intervals? It takes time for your heart rate to come back down, but you’re aiming for 70% since that’s the intensity of exercise where your body can clear lactate most efficiently (to be ready to go again). 

• Did you finish the workout feeling like you could have done at least one more round? You’re not trying to completely exhaust yourself, just give yourself a challenging workout. 

If you didn't do the workout properly, don't beat yourself up—just take note of where you can improve next time. Any kind of cardio is good for you, and gives you a foundation to build on.

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