[0:00]This study came out in 2007 and it blew up. The Norwegian 4x4 is scientifically proven to increase your VO2 max by 13%. This is one of the best ways to improve your VO2 max. The magical Norwegian 4x4 minute intervals were everywhere. Because of this study, every coach I had prescribed 4x4s. And I've done well over 100 of these kind of sessions, and it came at a price, which I'll get into later in this video. But since then, I've been very skeptical to the whole training approach. So I went back and actually read this original study line by line, and I found things that honestly shouldn't happen in publicly funded sport science communication. Here's the uncomfortable truth. This study never proved what most people think it proved. And what was claimed afterwards and how it is still referenced today is kind of hard to believe. I'm Joren, I'm a physiotherapist, coach and an athlete myself. And in this video, I'll show you what the study actually says and how the Norwegian 4x4 intervals became one of the biggest global training myths. Before we look at what this study actually did, it's important to understand what people were told about it, and how the findings actually were communicated. I was a young ambitious athlete when this study first came out, and my coaches told me about this magical Norwegian study that had found an optimal way to increase VO2 max, called the 4x4. You run for four minutes really hard, then three minutes easy and you repeat that four times. Looking back at how the offers drew conclusions from their data and how they later marketed the whole training idea, I can fully understand why this became so widespread. This is a book released by the sport scientist behind the 4x4 method. And just reading the blurb says a lot about how the Norwegian 4x4 was presented to the public. Whether you are an elite athlete or a patient, four times four minutes of intensive intervals or repetitions are the key to improving health and performance. In other words, this specific interval structure was framed as a universal endurance solution for everyone. So this is how the method was framed by the two professors behind the study: Revolutionary, universal, the gold standard, the key. And this book, released as recently as in 2024, is not a misrepresentation of how the two offers behind the study have promoted the 4x4 from the beginning. These claims have been repeated in articles, in interviews for almost two decades now. For example, in a TED talk given years before this book was ever released, one of the offers says this. the most effective exercise that we know of for your cardiovascular system, the 4x4 minute intervals. If you're carrying out this type of training, you improve half a percent each time you exercise. And here is an example from a Norwegian news article where the other main professor behind the 4x4 studies says, "Our research shows that long runs at 70-85% of maximum effort do not increase oxygen uptake for recreational athletes." Forget conversational pace and prioritize intervals. These are very strong claims and all of this was linked back to this study. A study from 2007 from a public university, widely referenced as the scientific proof behind this revolutionary method. The title of the study is Aerobic high-intensity intervals improve VO2 max more than moderate training. So if you are a coach, an athlete or a young ambitious runner at the time, like myself, this is what you heard. 4x4 is revolutionary, 4x4 works for everyone, 4x4 is the key to development, 4x4 is scientifically proven. And you still hear this today directly from the same researches and across many media outlets. But now let's get to the interesting part and separate what was claimed and see what this study actually showed. Because when you read this study and try to understand it, it tells a very different story.
[4:35]The participants in this study were moderately trained young men. They were not beginners, they were already training at least three times per week according to the study. They were then randomly assigned into four different training groups. And for eight weeks, all training outside of the study was removed. Everything they did training-wise was scientifically defined by the exact study protocol for the different groups. Now to understand this, let's go through the four groups one by one. The first group did what the offers labeled as long slow distance, but it wasn't actually that long. They ran for 45 minutes at around 70% of maximal heart rate three times per week. That gives a total weekly training time of 2 hours and 15 minutes. The second group trained at what the offers called lactate threshold intensity. They ran just over 24 minutes per session at about 85% of maximal heart rate. Including warm-up and cool-down, their total weekly training volume was just under two hours. The third group did short intervals. 15 seconds hard, then 15 seconds easy, repeated 47 times per session. Including warm-up and cool-down, they also trained just under two hours per week. The fourth group did the now famous 4x4 intervals, four minutes hard, three minutes easy, repeated four times. So if we look at this objectively, what what do we have here? We have four groups, training almost the same total amount of time each week, roughly two hours.
[6:08]One group doing only easy training, one doing moderate training, but still at very low total volume, and two groups doing very high intensity interval training three times per week. And remember, these people included in the study were already trained athletes. For the first group, just doing three 45 minutes short easy runs per week was most likely a significant reduction in their normal weekly training load. So when I look at this setup, I honestly don't need a study to tell me that groups doing hard intervals three times per week will improve their VO2 max, more than the two groups doing very little volume and no high-intensity work. In many ways, you could say that the outcome was pretty much built into the design of the study. And that's exactly what happened. Both the two interval groups improved their VO2 max, more than the easy and moderate group which basically stayed on the same VO2 max during the eight weeks this training protocol was done. But when you actually look at the data more closely, something very important appears. The 15-15 interval group and the 4x4 minute interval group improved almost the same amount.
[7:28]In fact, the 15-15 group started with a higher baseline VO2 max, averaging 60.5, compared with the 4x4 group that started at 55.5 as an average. And normally, starting at a higher level of VO2 max makes it further improvement harder or requires more training. Despite that, their improvements were very similar. And the study actually states it itself. There was no significant difference in training response was observed between the 15-15 group and the 4x4 group. And this matters because this study did not show that 4x4 was superior to other high-intensity interval performance when it comes to improving VO2 max.
[8:06]What it actually showed was something much narrower.
[8:14]So let's be very clear about what this study actually say. It can say that when weekly training volume is low, and training is limited to three short sessions per week, high-intensity interval training, regardless of the exact interval structure, improves your VO2 max for moderately trained runners. It can also say that even three short and easy 45-minute jogs per week are enough to largely maintain the VO2 max over the short term in moderately trained people. And that is a reasonable conclusion and in itself this can be interesting. But here's what this study cannot say. It cannot say that 4x4 is the best endurance training method.
[8:58]It cannot say that 4x4 works for everyone. It cannot say that this kind of high-intensity interval work is the training solution for all recreational athletes. And it absolutely cannot say that this is how endurance athletes should train all year round. Yet, that is very close to what was actually communicated by the team behind this study. And to say that 4x4 is optimal for improving VO2 max based on that study is simply not correct. The 15-15 second intervals showed the same result with no significant difference shown. And if you look beyond this paper at a study like this one that was done by another research team that compared different interval models and check the VO2 max outcomes. It shows exactly what you would expect. In this one, they compared eight minutes times 4 by 4 by 4. And they showed that the eight minutes by four had greater VO2 max improvements than the 4x4. And that's not surprising. That's simply training volume doing what training volume does. So if you say that 4x4 is optimal, why not say that 8x4 is optimal? But yes, they are right about one thing in this first study that 4x4 can improve VO2 max in the short term and be a great workout for working on that. But the way this study is built tells us almost nothing about real world endurance training. Because the entire reason endurance athletes have always done and still do a lot of low-intensity training and a lot of threshold training is that it allows for a higher total training volume over time. And hard near all out intervals are effective, but they're also costly. You cannot do them endlessly without consequences. So to design a whole study where all groups are forced into lower weekly volume than they normally train and then generalize those results and findings in there to long-term endurance training is highly problematic. But the real problem begins when this short-term, high-reward approach is presented as the main pillar of endurance training, because this kind of training carries a higher injury risk and a higher burnout risk. Anyone who has actually done one of these 4x4 sessions at 90% of maximal heart rate knows that they are really demanding both physically and mentally. So to present this as the simplest and easiest solution for everyone is a massive oversimplification. Training shouldn't just work in a lab for eight weeks. It should work for years. And so far, I have never met someone who can sustain two or three of these super hard interval training sessions week to week, year after year without any problems. And at least in my opinion, that is not a sustainable lifelong training model. And to then say that lowering the intensity gives you almost no benefit is honestly just sad to hear and simply not true. But I want to be very clear here. I'm not saying that VO2 max, this super high-intensity intervals like 4x4 are bad. I still do this type of work myself and I prescribe it to my athletes as well. But I do it at specific times in specific phases of the training cycle, often as a sharpening tool toward shorter races. Not as the whole foundation of endurance training. And yes, if you can hear that I'm getting a bit riled up and frustrated, that's because this is a bit personal for me, because the way this study was designed and especially how it was communicated, shaped a large part of my own training growing up. I just heard this was scientifically proven to be the best way to train by researchers in Norway and this magic 4x4 will make you so much faster. And threshold training was even described as something with little or no real benefit, something you should stay away from. And looking back, I genuinely believe that building my training around very high-intensity 4x4 intervals played a major role in the years of serious running injury problems I struggled with. And when I go back, read the original study carefully, read the articles, listen to that TED Talk, and see that the same people are now selling books and training apps built entirely around this 4x4 concept, it becomes very clear to me that this story isn't primarily about good evidence-based training and science. It's about how powerful marketing can be when it's wrapped in a scientific authority. The interesting thing is that while these so-called Norwegian 4x4 intervals are still marketed in many places as the gold standard and still hyped in many training spaces, big parts of the endurance world has actually moved on. And it has moved on in a direction that is still heavily influenced by Norway, but almost completely in the opposite direction of what the 4x4 came to represent. This is where a lot of confusion also comes in. I constantly see people talking about the Norwegian method and 4x4 as if they were the same thing, even though they are absolutely different ways of training. I even see videos like this on YouTube claiming that 4x4 is the secret behind Jakob Ingebritsen's success. But the Norwegian method that Jakob and others have made famous is not built around frequent high-intensity VO2 max sessions. It's built around high total training volume, a large amount of carefully controlled threshold work and relatively few true high-intensity sessions that push you to the absolute top end of the VO2 max like the 4x4 does.
[15:21]And this approach, the real Norwegian method, aligns much better with what we know about long-term training adaptation, durability, injury risk and sustainable progression over years. If you want to learn more about the modern Norwegian method, the principles behind it and how it can be applied in practice, you can check out this video here. Train smart, have fun, and I'll see you in the next video.
