I don’t think the 3% was an annual metric; instead they simply looked retrospectively at cohorts of subjects whose VO2 max was down by 3% or worse, stable, or increased by 3% or better. The outcome measure over a mean of 6.7 years was incident prostate Ca.

Importantly, the study says nothing about how the subjects achieved this result or whether it was an active process at all. The author’s comments and the first sentence in The Guardian overstate the actual findings. It’s reasonable to assume that purposefully pursuing a cardiovascular fitness regimen aimed at improving VO2max will reduce your prostate Ca risk but the study doesn’t address that.

Yeah, I thought of the same, a 3% year-on-year improvement must necessarily hit some ceiling at some point. The study didn't get into _how_ to achieve a 3% improvement, but from how I understand it, looked at the average year-on-year decline, stability, or improvement, over a period of 7 years.

My own take-away is that there's even more data that confirms "being fit" is about a continuous effort, and that putting in an effort (even quite minimal) to stay fit comes with a whole range of positive health benefits.

I wouldn't extrapolate too far like that.

If you start from next to nothing, you can sustain 3% growth per year for 33 years until you reach 100% growth. That is 33 years to go from lifting 50lbs to lifting 100lbs. You'd actually probably have to work hard to improve that slowly. For cardio that's going from a 20 to a 10 minute mile over 33 years. After a plateau, you generally need to train smarter rather than harder, and then you can keep gaining.

Even if you can't sustain it forever, you're getting fitter than if you weren't doing anything, so your life expectancy is still getting longer.