The Norwegian 4×4: the real protocol, the studies, and what they do not prove

On this page

1. The protocol
2. What the studies measured
3. How many times a week
4. It is not the double threshold
5. Limits
6. Sources

The protocol

The 4×4 comes from the cardiac exercise research group at the Norwegian University of Science and Technology (NTNU, Trondheim), which uses it in its studies and recommends it on the CERG group's public site. The structure, as the researchers describe it:⁴

Two clarifications from the researchers that get lost on social media. First: if you cannot complete the four minutes, you are going too hard; the right intensity leaves you short of breath but able to finish all four intervals. Second: there is nothing magic about the number four. The group recommends intervals of at least two minutes and at least fifteen total minutes of high intensity per session: 8×2 minutes or 3×6 minutes work too.⁴

On maximum heart rate: formulas like "220 minus age" carry wide individual error. The CERG group suggests measuring it with a field test (after a warm-up, two four-minute intervals, then a third one finished as fast as you can sustain) and uses uphill walking or running for the intervals, to reach the right intensity with less joint load.⁴

What the studies measured

The reference study is Helgerud and colleagues, 2007, in Medicine & Science in Sports & Exercise: forty healthy, moderately trained men, randomly assigned to four protocols with the same total work, three times a week for eight weeks, on an uphill treadmill.¹

• 4×4 at 90-95% of maximum HR: VO2max +7.2%, the change reported by the authors (the absolute mean values cited in the abstract are not arithmetically consistent with this percentage, so we do not report them).
• 47 repetitions of 15 seconds at the same intensity: +5.5%, not significantly different from the 4×4.
• Continuous threshold running (85%) and slow running (70%): no change in VO2max.
• Cardiac stroke volume rose by about 10% only in the two interval groups; the authors link the VO2max improvement to this.
• Running economy improved in all groups, with no differences between them.

The same protocol has been tested on very different populations. In stable post-infarction heart-failure patients (Wisløff 2007, Circulation, twenty-seven patients followed for twelve weeks), 4×4 uphill walking raised VO2peak by 46% versus 14% for moderate continuous training, with signs of favourable left-ventricular remodelling: a study on selected, supervised patients, not a do-it-yourself prescription.² In the Generation 100 study (Stensvold 2020, BMJ), 1,567 adults aged 70-77 followed two weekly sessions of 4×4 or moderate activity, or the national guidelines, for five years: no significant mortality difference between groups, with a trend favouring the interval group and better fitness and perceived quality of life.³

How many times a week

The CERG group's answer: one interval session a week is enough to maintain fitness; improving it takes two or three sessions. In one of their studies with five to eight interval sessions a week, motivation collapsed and those approaching eight sessions became overreached without the expected adaptations. More intensity does not mean more sessions.⁴

It is not the double threshold

The 4×4 is often presented as "the Norwegian method of champions". That is a mix-up. Norwegian middle-distance results are built on lactate-guided threshold work: repeated sessions at threshold intensity, two on the same day, with capillary lactate held typically between 2 and 4.5 mmol/L and measured every one to three repetitions. The model described in the literature (Casado 2023) includes three to four such sessions plus one VO2max-intensity session per week, inside a high weekly volume that is almost all easy.⁵ The 4×4 works at much higher intensity: four minutes close to the aerobic maximum, against repetitions held just below the threshold measured in the field with lactate. They are different tools, born in different contexts (health research in Trondheim versus elite training), and they should not be stacked: for anyone already running a lot, adding 4×4 on top of high volume is the fastest way past the limit the researchers themselves describe.⁴

For the double threshold see our analysis of the lactate-guided Norwegian method; for placing hard sessions in the week, polarized or pyramidal. The "session that builds champions" claim is not supported by the cited studies: the studied populations are moderately trained amateurs, cardiac patients and adults over 70, not elite athletes.

Limits

• The 2007 study has forty participants, all male, moderately trained: the numbers do not transfer automatically to women, elites or sedentary people.
• The comparison is at matched total work: it does not say that swapping easy kilometres for intervals is the best strategy in a real training week.
• Mortality in Generation 100 did not differ significantly: a trend is not proof.
• Heart-rate percentages assume a measured maximum HR, not a formula estimate.

Sources

1. Helgerud J. et al., Aerobic high-intensity intervals improve VO2max more than moderate training, Medicine & Science in Sports & Exercise, April 2007. PubMed abstract. Protocol, per-group results and authors' conclusions read.
2. Wisløff U. et al., Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients, Circulation, 2007;115:3086-3094. PubMed abstract. Design, uphill-walking 4×4 protocol and results read.
3. Stensvold D. et al., Effect of exercise training for five years on all cause mortality in older adults: the Generation 100 study, BMJ 2020;371:m3485. Full text. Results and author-stated limitations read.
4. Cardiac Exercise Research Group (CERG), NTNU, Exercise advice and 4×4 recommendation pages. ntnu.edu/cerg/advice. Recommended frequency, common mistakes, max-HR field test and equivalent variants read.
5. Casado A., Foster C., Bakken M., Tjelta L.I., Does Lactate-Guided Threshold Interval Training within a High-Volume Low-Intensity Approach Represent the "Next Step" in the Evolution of Distance Running Training?, International Journal of Environmental Research and Public Health, 2023;20(5):3782. Full text. LGTIT model, 2-4.5 mmol/L lactate target, weekly structure and elite context read.

Sources read on 7 November 2026. Heart-rate percentages assume a measured maximum HR.

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