Norwegian 4x4 intervals: the workout that raises VO2 max

The Norwegian 4x4 is four hard four-minute efforts with three minutes of easy movement between them. It comes out of a research group in Trondheim, it is one of the most tested interval sessions there is, and it raised VO₂ max more than steady training of the same total work. Here is the protocol, the evidence, and how to fit it into a week.

What is the Norwegian 4x4 workout?

The session has four parts:

1. Warm up for about ten minutes at an easy to moderate pace.
2. Run four intervals of four minutes at 90 to 95% of your maximum heart rate.
3. Recover for three minutes between intervals, still moving, at about 70% of maximum heart rate.
4. Cool down for a few minutes easy.

The whole thing takes a little under forty minutes. It works on a treadmill, a track, a hill, a bike or a rower; what matters is the heart rate, not the mode.

Free tool: Two numbers from your watch give five zones that fit your heart, not an average one. Open the heart rate zone calculator →

What did the trials find?

Helgerud and colleagues assigned 40 moderately trained young men to four programmes, three sessions a week for eight weeks, with the total work matched across groups. Two groups trained continuously, at 70% and at 85% of maximum heart rate. Two did intervals: 15 seconds on and 15 off, or the 4x4. Only the interval groups improved VO₂ max significantly more than the steady groups. The 4x4 group went from 55.5 to 60.4 ml/kg/min, a 7.2% rise, and stroke volume, the amount of blood the heart pushes per beat, increased by about 10% after interval training.

The longest test is Generation 100, which randomised about 1,500 Norwegians aged 70 and over to twice-weekly 4x4 sessions, moderate continuous training or the national guidelines for five years. The 4x4 group gained the most fitness and reported the best quality of life. Deaths were 3% in the 4x4 group, 6% in the moderate group and 4.5% in controls, but the difference was not statistically significant, and the authors say the study does not prove the intervals extend life.

PeakVital does this from your own data. Three tests. One number. Your real age. Join the free beta →

How hard is 90 to 95% of maximum heart rate?

Hard enough that you can only say a few words at a time by the end of each interval, and not an all-out sprint. The first interval often feels too easy for the first minute because heart rate lags behind effort; by the third minute you should be in the target range.

The percentage only works if your maximum heart rate is right. The formula 220 minus age is off by ten beats or more for many people. The heart rate zones guide shows how to find a usable maximum from a hard effort you have already recorded. If you have no heart rate data, run each interval at a pace you could just hold for about eight to ten minutes in a race.

How often should you do it?

The young men in the 2007 trial did three sessions a week for eight weeks; the older adults in Generation 100 did two. For most people training for health, one 4x4 a week alongside two or three easy sessions is enough to see VO₂ max move, and it leaves room to recover. Two a week is reasonable once one feels routine. Doing it every day defeats the point, because the adaptation happens between sessions.

• Weeks 1 to 2. One session, three intervals instead of four, aiming for the low end of the range.
• Weeks 3 to 6. One session, four intervals, the full range.
• Week 7 onward. A second session if your easy days still feel easy and your recovery signals are steady.

Retest your VO₂ max after six to eight weeks with the same method you used at the start.

Who should be careful with it?

Hard intervals are safe for most healthy adults, and they are used in cardiac rehabilitation under supervision. In Norwegian rehab centres, Rognmo and colleagues counted one cardiac event per 23,182 hours of high-intensity training among 4,846 patients with coronary disease, against one per 129,456 hours of moderate training. Both rates are low, but the higher one is a reason to talk to a doctor first if you have heart disease, symptoms on exertion, or have been sedentary for years.

Beta blockers and some other drugs blunt heart rate, which makes percentage targets meaningless. In that case, use effort instead of heart rate. And if you have no aerobic base at all, a few weeks of easy zone 2 work first makes the intervals more productive and less miserable.

How PeakVital fits

PeakVital measures VO₂ max every six weeks the same way, so a block of 4x4 sessions shows up as a number that moved or did not. It is coming soon for Android and Wear OS, in private beta.

Hen Eytan · Founder, UPeak

Builds the UPeak apps and writes up the research behind them.