How do you run the Norwegian 4x4?

What heart rate should the Norwegian 4x4 be run at?

90 to 95% of your max heart rate. That's the band prescribed in the Norwegian trial behind this session, run by 40 moderately trained men on a treadmill.

On the five-zone model, Zone 4 tops out at 90% of max and Zone 5 runs from there up, so the band straddles them. If you're asking whether the 4x4 is a Zone 4 session or a Zone 5 session, it's both, in that order. The HR Zone Calculator gives you both ranges in beats.

If you've seen 85 to 95% elsewhere, that number has a real source too. The Trondheim research group that developed the protocol publishes 85 to 95% for its own public programs. That claim shows up in an answer about a study of very obese teenagers on treadmills. The same group's advice page asks you to reach 90% during the first interval.

This percentage isn't 90% of your heart rate reserve. The Trondheim group states the target as a share of your actual max heart rate, resting heart rate left out. Putting it in changes the whole scale.

How should you warm up for the Norwegian 4x4?

10 minutes of easy running, at 60 to 70% of your max heart rate. That's what the Trondheim group prescribes for this session, and it's enough.

The warm-up has one job here beyond the usual. Your first interval takes the longest to reach the band, and the gap it has to close is why. You arrive at it with your heart rate down in warm-up territory and four minutes to drag it up. Finish the warm-up already breathing hard, and start the first interval straight off the back of it.

A harder piece in the warm-up, a few minutes near threshold, has a real effect in the lab. How hard it should be and how long before the session it should end aren't settled. A 2023 review of that research says the optimal intensity and recovery duration of exercise performed before competition "remain unclear." So the hard work goes in the intervals, and the warm-up stays easy.

Finish the session with 5 minutes at the same easy intensity.

How hard should the first interval be?

Hard enough to reach the band inside the four minutes, and no harder. The fourth interval should look like the first.

The group that developed the protocol says to be equally tired after every interval, and to save any real emptying for the last one. Go out too hard and, the group says, the lactate build-up keeps most people from reaching the target in the intervals that follow.

There's no pace to give you. The speed that puts you in the band is yours, and it isn't the same speed for all four intervals. When 39 active adults rode this session on a bike, the resistance was adjusted through each interval to hold them in the band. The work rate came down interval by interval while their heart rate went on climbing. If rep four is slower than rep one at the same heart rate, that's the normal shape of the session.

What should your heart rate do during the intervals?

Reach 90% of max inside the first interval, and take one to two minutes to get there in the ones after. That's the Trondheim group's own expectation.

So the number reads low at the start of every rep, because it's still on its way up. Running harder in the first 30 seconds to force it up is the most common way to wreck the session. You spend the effort on a number that was going to arrive anyway, and rep three pays for it.

RunBeat's Timed Intervals has the Norwegian 4x4 as a preset, so the clock runs the phases by voice while you watch the band:

Timed Intervals in RunBeat RunBeat calls every work and rest phase, and your Apple Music playlists switch with it.

When 39 active adults rode the 4x4 on a bike, 12.9 of the 16 working minutes landed inside 85 to 95% of max heart rate. The split was uneven: 2.7 minutes in the first interval, against 3.4 to 3.5 in each of the three after it. Nothing is wrong with your first interval when it does that.

Heart rate reading high on your easy runs is a different problem with a different fix.

What should you do in the three minutes between intervals?

Jog. Three minutes at 60 to 70% of your max heart rate, moving the whole time.

The spec in the trial is an active jog at 70% of max rather than standing rest. That intensity isn't arbitrary. The Norwegian group that developed the protocol says you clear lactate fastest at around 70%.

The same group's public programs say three minutes of relaxed walking. Those are written for people walking or running up a hill rather than running intervals. The instruction underneath is the same either way. Keep moving, and keep the number near 70%.

Your heart rate won't fall far in three minutes. You start each new interval from around 70% rather than from rest. That's why the later ones reach the band faster than the first one did.

How do you know you ran the session right?

You should finish feeling capable of a fifth interval. The Trondheim group puts the test in exactly those terms: "You should feel capable of doing another interval after you've completed the four." If that seems impossible, the session went too hard.

That's the whole standard. There's no pace to hit and no distance to cover.

Running the last interval at 95 to 100% of max isn't dangerous, but the same group calls the extra benefit "practically negligible compared to staying at 90%." Running the last interval to exhaustion buys nothing.

If you couldn't hold the band by the third interval, the first one was too hard. Take the next session out a little slower.

How do you run the Norwegian 4x4 on a treadmill?

Set whatever speed and incline put you in the band, and reach for incline before speed. What you're holding is a heart rate, and the belt speed is only how you get there.

That's what makes a treadmill a good machine for this session. Outdoors you're guessing at the effort that produces 90% of max and adjusting by feel. On a belt you dial it in and the machine holds it. The Norwegian group behind the protocol programs its intervals uphill or on an inclined treadmill for that reason. A high heart rate arrives more easily uphill, and your knees take less of the run.

One thing to expect indoors. At efforts this hard, a flat belt costs you less oxygen than the road does. The speed that puts you at 90% indoors will be faster than the one that does it outside. Add incline rather than chasing the number with speed alone.

Your treadmill's speed display and the 1% incline habit are their own arguments. Neither changes this session, because you're steering by heart rate either way. For the recovery, drop the speed or the incline and keep the belt turning.

How often should you run the Norwegian 4x4?

Twice a week, at least 48 hours apart, for 6 to 8 weeks.

The Trondheim group recommends two to three interval sessions a week to raise fitness. One a week, it says, is enough to hold what you have. We run two, because the third session comes out of the easy running that makes the first two repeatable.

We keep at least 48 hours between the two sessions, because the session takes more out of you than its 16 working minutes suggest. The same 48 hours sits between the second session and the long run.

We run the block for six to eight weeks, because that's the span the results were measured over: the trial ran 8 weeks and the group's own public program runs 7. After that, one session a week holds the gain while the rest of the week goes back to easy running.

If interval work is new to you, start with one session a week and add the second in week three.