Dr. Tommy Wood says six months of Norwegian 4x4 intervals protected older adults' hippocampus for five years

The wellness internet has spent years treating cortisol like a haunted doll in the attic. On Huberman Lab, Dr. Tommy Wood offered a less cuddly, more useful claim: older adults who did Norwegian 4x4 intervals three times a week for six months had hippocampal benefits that were still measurable five years later.

That is not a vibes-based endorsement of suffering in moisture-wicking shorts. Wood was comparing exercise studies in older adults, and the point was specific enough to survive the podcast-to-Reddit pipeline: zone 2 helped, but high intensity interval training looked better for hippocampal structure and function, the brain territory everyone invokes when the topic is memory, aging, and please God where did I put my keys.

The brain liked the hard version

Wood first gave the standard aerobic exercise story, the one many exercise people already know by heart. In older adults, brisk walking three times a week can move the needle on the hippocampus. Nothing wrong with that. It is the sensible sedan of brain health advice.

40 minutes brisk walking three times a week for a year. And they saw significant increases in the volume of the hippocampus uh increases in V2 max fitness, increases in circulating BDNF levels

Then came the less comfortable comparison. Another study put older adults into low intensity, zone 2 style treadmill work, or a high intensity interval group. The interval protocol was the Norwegian 4x4, which is not a hygge-adjacent wellness ritual. It is four minutes hard, three minutes not hard enough to forget what just happened, repeated four times.

4 minutes 85 to 95% of maximum heart rate. They had a threeminute rest in their protocol. They did that four times over.

Huberman, correctly, reacted like a man who has seen the inside of an interval workout and still has emotional paperwork pending: that is really hard. Wood agreed. Three times a week for six months is not a casual prescription. It is a relationship with a treadmill.

But the reported payoff is the whole reason this episode has a claim worth publishing. The high intensity group improved fitness about as well as the zone 2 group, Wood said, but showed better hippocampal results on function and MRI, and those gains were maintained five years after the intervention. Five years is the detail that matters. Six months of unpleasantness buying half a decade of measurable brain benefit is exactly the kind of claim people Google before doing something rash with a heart-rate monitor.

they basically show that the harder people worked um and the more cortisol they released, the better the benefit.

Cortisol is not Voldemort

The most useful part of Wood’s argument is not that everyone over 60 should immediately become a Norwegian interval hobbyist. Please do not make your first workout a midlife hostage negotiation. The useful part is the correction to a very dumb cultural reflex: cortisol bad, stress bad, intensity bad, therefore anything that makes you breathe like a tax audit is aging you in real time.

People have conflated acute stresses versus chronic stresses.

Wood’s distinction is the whole ballgame. Chronic stress, bad sleep, metabolic disease, and never getting to recover are not your friends. Acute stress that you can adapt to is basically the operating system of training. This is why the anti-cortisol content mill is so silly. It sees a smoke alarm and blames the battery for the fire.

The verdict here is strong but narrow. Wood is leaning on actual intervention data, not gym folklore, and the five-year follow-up makes the claim unusually sticky. Still, this is not a universal mandate. It was older adults, a specific protocol, and a hard dose. Wood himself later says that for sustainability, one high intensity day a week may be plenty for many people, especially if they are also lifting.

The less sexy prescription is both

What keeps this from becoming another bro-science sermon is that Wood does not crown one training style king of the cortex. He argues that aerobic work and resistance training seem to hit different brain systems. Cardio, especially across the intensity spectrum, is tied in his telling to gray matter and memory. Resistance training appears to benefit white matter and executive function. The adult brain, annoying as ever, wants variety.

That fits the bigger theme of the episode, which is that neuroplasticity is not a magic spell. The brain changes when it gets inputs that are demanding enough to matter. Dancing, ball sports, martial arts, language learning, lifting, intervals, all of it beats the elegant death spiral of doing only the things you’re already good at.

I think if you want it to be sustainable for long periods of time, like I would typically say one day of highintensity work is fine, right?