What is the Norwegian 4x4?
The 4x4 method comes from the Cardiac Exercise Research Group at the Norwegian University of Science and Technology (NTNU) in Trondheim. It is a simple, structured interval workout designed to improve your maximal oxygen uptake, or VO2max: the most oxygen your body can use during hard exercise.
VO2max is one of the strongest markers of health there is. People with higher fitness live longer and have fewer heart problems, and the 4x4 is one of the most time-efficient ways to raise it.
This program is our own free guide to the method, based on the published research. We are an independent website and are not affiliated with NTNU or its researchers.
Why it works
Four minutes is long enough for your heart to work near its maximum capacity for a sustained period, which is the main signal for it to become stronger and pump more blood per beat. The three minutes of easy movement let you recover enough to do it again, four times.
In a study of healthy young men training three times a week for eight weeks, the 4x4 group improved VO2max by about 7%, while groups training at a steady, moderate pace did not improve significantly. The method has since been used with heart patients, older adults and athletes.
A five-year study of more than 1,500 Norwegians aged 70–77 found that 4x4 training twice a week was safe, and the group doing it had the lowest death rate of the three groups, although that difference was not statistically certain.
How hard is 85–95%?
Hard, but not a sprint. You should be breathing heavily and able to speak only a few words at a time. On a 6–20 effort scale it is about 16–17: “hard” to “very hard”. The last interval should feel like the toughest, but you should still be able to complete it at the same pace as the first.
Finding your heart rate zones
Researchers from the same university developed a formula for maximum heart rate from a study of thousands of healthy Norwegians: 211 − 0.64 × age. It is more accurate for adults than the old “220 minus age”. Use the calculator above to get your zones, or look up your age in the table in the PDF.
Choosing your exercise
Anything that uses large muscle groups and lets you work hard for four minutes will do:
- Uphill walking or running on a treadmill (5–10% incline makes it easier to reach the zone).
- Cycling outdoors or on an indoor bike.
- Rowing or a ski machine.
- A steep hill outside: walk or run up for four minutes, walk down to recover.
Before you start
If you have heart disease, high blood pressure, diabetes or another medical condition, or have been inactive for a long time, talk to your doctor before starting high-intensity training. Stop and seek help if you feel chest pain, dizziness or unusual shortness of breath.