This health metric is probably one of the best predictors of lifespan, more so than cholesterol, blood pressure, and even more than whether or not you smoke.

VO2 max is the maximum amount of oxygen your body can take in and actually use during all-out effort.

I often describe it as the size of your “engine.” A bigger engine means your heart, lungs, blood, and muscles are better at the job that keeps you walking up stairs at 90 without sitting down halfway: moving oxygen from the air into working cells.

Here’s a couple things that from the full letter that reframed how I look at my training (and gave me a bit of optimism):

• In an observational study of 122,007 people, the least-fit group was more likely to die over the following years than the smokers were. In fact, the least fit group, when compared to people of just average fitness, carried close to triple the risk of death; compared against the fittest, it ran to about five-fold.

• After about age 25 to 30, a sedentary adult loses roughly 10% of their VO2 max per decade, and the decline tends to accelerate later in life.

• BUT…training consistently can roughly halve the rate of decline per decade. In a meta-analysis of 41 controlled trials in previously sedentary adults over 60, an aerobic training program raised VO2 max by about 16% on average. That is massive, and that means that it is definitely not too late to start making big improvements on your health.

• Plus, you don’t need to be an elite athlete to reap the benefits of increasing your VO2 max. In the observational study I mentioned before, people of just above-average fitness had roughly a 64% lower risk of death than the least-fit group. Not Olympians, just a bit over average. There’s no pill on earth with an association that size, and this one is free.

I'm a PhD scientist, and my job here is to help you separate what's real from what's being sold to you. I went through the actual, published research: what’s just observational data, what we know about VO2 max and brain health, the science backed ways to increase your VO2 max, and the mistakes people make that can slow down months of progress.

The full breakdown, with every study linked, is in my letter, and the full first section (covering the critical science) is free to read.

Go take a look, then go get your engine running today🫀