What the Experts Say About VO2 Max and the 4x4

None of the experts named on this page has any affiliation with Viking 4x4. This page documents their public statements about the protocol and VO2 max, with links to the original sources.

Across longevity medicine, exercise science, and cardiology research, the experts who read the mortality data land in the same place: VO2 max is one of the strongest predictors of lifespan we can measure, and hard intervals in the 4-minute range — the Norwegian 4x4 pattern — are among the best-evidenced ways to raise it.

That convergence is unusual. These five people disagree about plenty — protein, fasting, training volume. On VO2 max they do not. Here is what each has actually said, paraphrased and linked so you can check the sources yourself.

Where do the experts agree?

What does Peter Attia say?

Attia's argument, laid out in The Drive #176 / AMA #27, is a walkthrough of the Mandsager 2018 dataset: 122,007 patients, treadmill-tested, followed for about a decade. Moving from the bottom fitness quartile to merely below-average was associated with "a 50% reduction in mortality over a decade," and bottom-to-elite was "a five fold difference in mortality" (AMA #27 clip). In the same analysis, low fitness carried more mortality risk than smoking (~41%), type 2 diabetes (~40%), or coronary artery disease (~29%).

His prescription is a dedicated weekly interval session of 4 minutes hard, 4 minutes easy, for 4–6 rounds — a variant of the NTNU 4x4 with a minute more recovery (his Zone 5 clip). Full breakdown, including how his variant differs from the studied protocol, on the Peter Attia page.

What does Rhonda Patrick say?

Patrick made her position unambiguous in a December 2023 post on X: VO2 max is "one of the best indicators of improved healthspan and lifespan," and the Norwegian 4x4 is "One of the best protocols for improving VO2 max." In a FoundMyFitness episode with Brady Holmer, she compared the 4x4 against 1-on/1-off intervals and Tabata; their shared conclusion is that longer intervals in the 2–4 minute range are particularly effective for VO2 max because they maximize time near maximal oxygen uptake.

She is equally clear that untrained people should not attempt the full protocol on day one — participants in the 2-year Dallas trial took months to build up to it. Her statements, cautions, and sources are collected on the Rhonda Patrick page.

What does Layne Norton say?

Norton is the lifting-side voice here, which makes his agreement more interesting, not less. A powerlifter and nutrition scientist, he appeared on The Drive #163 — an episode centered on resistance training and body composition — and again on episode #205, where the conversation turned to what the mortality data reward: in his words, "Lean body mass is inversely proportional to your risk of mortality after age 50."

But his consistent public message is that muscle does not excuse you from cardio. His platform's guide to high-intensity interval training recommends adding 2–3 HIIT sessions per week alongside a lifting program, citing VO2 max and cardiovascular-health improvements that steady lifting alone does not deliver. The strength data and the fitness data are not competing claims; strength and VO2 max are independent predictors, and the experts who read both literatures train both.

What does Dr. Mike Joyner say?

Joyner, an anesthesiologist and human-performance researcher at the Mayo Clinic, is arguably the most credentialed VO2 max scientist alive — he wrote the famous 1991 analysis of what a 2-hour marathon would physiologically require. On The Drive #217 he laid out the case that cardiorespiratory fitness drives longevity through concrete mechanisms — blood pressure, autonomic function, endothelial function — and framed the actual goal memorably: "live a long time and then die quickly with minimal disability."

Joyner is less attached to any single protocol than the others; his consistent message is that regular vigorous aerobic work, sustained over years, is what moves the needle. The 4x4 is one well-evidenced way to package it, not the only one. He also emphasizes trackable proxies like heart-rate recovery — the same signal covered in the heart-rate recovery article.

What does Dr. Benjamin Levine say?

Levine is the researcher behind the study everyone else on this page cites. His team's 2-year randomized trial (Howden et al., Circulation 2018) took 61 sedentary adults aged 45–64 and trained them progressively — building to 4–5 sessions per week, anchored by one weekly Norwegian 4x4 session at over 95% of peak heart rate. Results: VO2 max up roughly 18%, and left-ventricular compliance — the youthful elasticity of the heart muscle — improved by more than 25%. Stiff, aging hearts became measurably more like young ones.

His own framing, from the UT Southwestern press release: exercise should be "part of their personal hygiene," like brushing your teeth, and this training dose "has become my prescription for life." His timing caveat matters too — an earlier trial in 70-year-olds found the window for reversing cardiac stiffening had largely closed, which is why he stresses starting in middle age. The 4x4 itself, and the Helgerud trial that made it famous (+7.2% VO2 max in 8 weeks), are detailed on the protocol page, and the longevity evidence is compiled in the VO2 max and longevity article.

Where do they disagree?

Mostly on packaging, not substance. Attia prescribes 4 minutes of recovery where the NTNU protocol uses 3, and runs up to 6 rounds instead of 4. Patrick sticks closer to the studied 4x4/3 format. Joyner declines to crown any single protocol, arguing the consistency of vigorous work over years dwarfs the details of interval structure. Norton weights resistance training more heavily than the others and treats HIIT as the efficient way for lifters to cover the cardio base. Levine's version is the most demanding in context — his trial embedded the weekly 4x4 in 4–5 total sessions per week, and he is blunt that a couple of token workouts will not remodel a stiff heart.

None of those differences touch the core claims: VO2 max predicts lifespan, it is trainable at any starting point, and repeated ~4-minute intervals near maximal effort are a proven way to train it.

What should you actually do with this?

Strip away the podcast hours and the consensus is short: get your VO2 max up, use hard intervals around 4 minutes to do it, once to three times a week, on top of an easy aerobic base — and build up to the full dose instead of starting there.

Where Viking 4x4 fits

Viking 4x4 exists to run exactly that consensus protocol: guided 4-minute intervals against your heart-rate zones, 3-minute recoveries, four rounds, with a per-interval heart-rate report and a 60-second heart-rate-recovery trend so you can watch the adaptation these experts describe actually happen. Other apps time your workout. Viking 4x4 shows your heart adapting.

None of the experts named on this page has any affiliation with Viking 4x4. This page documents their public statements about the protocol and VO2 max, with links to the original sources.