Norwegian 4×4 intervals

The session

Warm up for ten minutes at an easy pace. Then:

1. Four minutes hard.
2. Three minutes easy.
3. Repeat until you have done four hard efforts.
4. Cool down for five to ten minutes.

Thirty-five to forty minutes from door to door, and the hardest part of your week is done. That is the Norwegian 4×4, and if you only ever learn one interval session, this is the one.

The name comes from Trondheim, where researchers at the Norwegian University of Science and Technology (NTNU) have used the format in studies for nearly twenty years, and from the fact that half of Norway seems to do it on a Tuesday evening. The skiers at the lit tracks are doing it. The runners on the hills above the fjords are doing it. The pensioners walking up the steep streets in the Generation 100 study were doing it.

It fits the Nordic way because it is simple, short, needs no equipment and can be done anywhere with a hill or a stretch of path. A lot of easy, a little hard, and this is the hard.

How hard

This is where people get it wrong, in both directions.

The hard efforts should be at what the NTNU researchers describe as 85 to 95 per cent of your maximum heart rate. In plain words: by the end of the first minute you are breathing hard. By the second minute you can say a few words but not a sentence. By the fourth minute you want it to stop but could, if you had to, go another thirty seconds. Then it stops.

The test is the fourth interval. If the fourth is as fast as the first, you paced it right. If you were flying on the first and crawling on the fourth, you went out too hard. The NTNU advice is blunt about this: you should feel capable of doing a fifth interval when you finish the fourth, and if that seems impossible you were too exhausted. They also note that going to 100 per cent on the last one is not harmful but makes it harder to keep the habit week after week, for almost no extra gain.

The easy three minutes are a slow jog or a walk, not a stop. You should be ready to go again, breathing more or less normally, when the three minutes are up. Standing still makes the next effort feel worse.

It takes a minute or two to reach the right effort in each interval, which is normal; the researchers are happy as long as you get there in the first one. Do not sprint the start to get your heart rate up faster.

What the research found

Two studies are worth knowing about, because together they say who this is for: everyone.

The first is the one that made the session famous. In 2007 a group at NTNU led by Jan Helgerud compared four ways of training in forty moderately trained men over eight weeks, three sessions a week, with the total work matched between groups: long slow running, running at threshold, short 15-second intervals, and 4×4. The 4×4 group improved their maximal oxygen uptake, the standard measure of aerobic fitness, by about 7 per cent, more than any other group, and significantly more than the long slow and threshold groups. The study is published in Medicine & Science in Sports & Exercise.

The second is bigger and slower. The Generation 100 study, also from NTNU, followed more than 1,500 people aged 70 to 77 in Trondheim for five years. One group did two sessions a week of high-intensity intervals, mostly 4×4; one did two sessions of moderate continuous exercise; a control group followed the national activity guidelines. Published in The BMJ in 2020, the main finding was that the exercise groups combined did not live longer than the control group, who turned out to be very active anyway. But the interval group had the best fitness after one, three and five years, reported the best physical and mental quality of life, and showed a trend towards fewer deaths than the moderate group, a trend the researchers are careful to say was not statistically certain. The honest summary, in NTNU’s own words, is that people in their seventies can and should do hard intervals, and the research group now recommends it for older adults.

Keep both in proportion. One is eight weeks in forty young men; the other is five years in 1,500 pensioners. Neither says 4×4 is magic. Both say a hard, controlled four-minute effort, repeated, is a very efficient way to get fitter, at any age.

How often

Once a week, every week, for most people. That is what the three programmes on this site use, and it is enough to feel the difference inside a month.

Twice a week is what the NTNU studies did, with easy days between. If you are training five or six days a week and the long easy sessions are already in place, a second interval day is the next thing to add. More than two is counterproductive: you cannot recover enough to do them properly, and they crowd out the easy hours that build the base. The shape of the week is still a lot of easy and a little hard.

Put it on a fixed day. Tuesday evening is traditional, which is why the lit tracks are full then. Give yourself an easy day after it and do not do it the day before your long session.

On a hill

The best place to do 4×4 is up a hill, for three reasons the NTNU advice gives: it is easier to reach the right effort because you use more muscles, it is kinder on joints than fast flat running, and it is harder to cheat.

Find a slope that takes about four minutes to climb at a hard effort and three minutes to walk or jog down. A forest road, a ski slope in summer, a steep street. Run or walk up hard, come down easy, four times. If the hill is shorter, go up, down, and up again within the four minutes; if it is longer, turn round at four minutes and the descent is your rest.

If you are starting from nothing, walk it. Four minutes of hard uphill walking is a real interval, and a lot of the seventy-year-olds in Trondheim did theirs exactly that way. When the walk no longer gets you breathing hard, jog the first minute of each effort, then two, until you are running.

On a bike

Same session, same effort, on a bike or a turbo trainer. Four minutes hard on a long climb or into the wind, three easy spinning, four times. A gravel road climb is ideal because the surface stops you going too fast on the descent. On the flat, use a big gear and a headwind rather than trying to sprint; the aim is a sustained hard effort, not a full-out one.

The gravel and mountain biking page covers how Nordic riders train through winter, and 4×4 on the trainer in a cold garage is a large part of it.

On skis

This is where the session comes from. Classic or skate, four minutes hard up a long gradual climb at the lit track, three minutes easy back down or along the flat, four times. Skiing uses the whole body, so the effort comes easily; the difficulty is holding technique when you are breathing hard. Choose a track you know, do the first interval slightly under what you think you can hold, and let the fourth be the judge.

Without snow, skiers do the same on roller skis, or bounding up a hill with poles, which is the hardest version of all and the one that a cross-country ski race is built on.

In the water and on the trail

Swimmers and swimrunners do it in a pool as 4 × 200 to 400 metres hard with three minutes easy, or in open water as four minutes hard along the shore. Trail runners do it on a hill, above, and it is close to the best preparation there is for a race with a lot of climb. For an obstacle race, the hill version with a weighted rucksack on the last interval is a fair rehearsal for the course.

A year of 4×4

Start with 3×3: three minutes hard, three easy, three times. Do that for a month. Move to 4×3, then 4×4. Once 4×4 feels normal, make it harder by making the hill steeper or the effort slightly faster, not by adding intervals. Some people go to 5×4 before a big race; few need to.

It is a session you will do for years. It takes forty minutes, it works on a hill behind a housing estate in the dark, and the research says it keeps working at seventy. Put it on Tuesday, dress for it as the winter chapter describes, and go.