Quick, tell me the greatest predictor of how active you will be in old age. While you’re thinking about that, consider this: What’s the one measurement of your health that can tell you the chances of dying from any form of mortality? Give up? Okay. Here’s the answer. It’s this measurement referred to as Vo2 Max, and scores of people have no idea what it is, why it’s important, or how to manage it. Fortunately, you are a subscriber to the Vitruvian Letter, so you are about to answer all these questions. Get this—when looking at VO2 max in relation to all-cause mortality, we observe a clear trend. Simply elevating your VO2 max from ‘low’ (bottom 25th percentile) to ‘below average’ (25th to 50th percentile) is associated with a 50% reduction in all-cause mortality. When transitioning from ‘low’ to ‘above average’ (50th to 75th percentile), the risk reduction is closer to 70%! First, I’m gonna  give a down-and-dirty yet highly accurate definition of what Vo2 Max is. Here goes: VO2 max, or maximal oxygen uptake, is a measure of the maximum amount of oxygen a person can use during intense exercise. It reflects how efficiently your body can deliver and use oxygen when you’re working out at your highest capacity. Essentially, it gauges your cardiovascular fitness and endurance. Quick sidebar-people with low Vo2 Max did NOT do well with COVID. I don’t want to state the obvious, but of all the things you can do to protect yourself against COVID having a strong Vo2 Max ranks right at the top. If, like me, you are keenly interested in making your golden years truly golden and not just fools gold, you want to be able to be active, vibrant, and less likely to die in your senior years. Of all the things I write about, discuss on the podcast, and advise on, nothing is of greater importance for future human performance than one’s Vo2 Max. You’ve most likely seen people getting their Vo2 Max measured. This is when you see someone on a stationary bike or treadmill running or cycling with a face mask attached to a huge tube. It’s about an 8-minute session, highly uncomfortable, designed to measure your body’s ability to absorb oxygen when pushed. Why am I writing about this now? Well, it’s simple. I’m following the herd. That’s right, I’m following the big-time experts like Andrew Humberman, Peter Attia, and Rhonda Patrick. Every one of these big brains has recently had podcasts discussing the importance of Vo2 Max. Ben Greenfield is another who has spoken at length about its importance. Therefore, I thought it was time for me to jump on the train. That said, I’ve actually been measuring and managing my Vo2 Max for some time. This all started when I got my Peloton. Matt Wilpers told me during a Power Zone Max class we were going to be working on our Vo2 Max. “What’s this Vo2 Max of which you speak, Matt Wilpers?” Then I noticed on my Apple Watch there was a measurement for my Vo2 Max. Check yours. It’s there if you wear an Apple Watch. Word of warning, it’s not all that accurate. As with most wearables, it’s just an estimate based on your age, gender, weight, and activities along with your HRV and heart rate. I started paying attention, and this became my #1 measurement for determining whether or not I was in “good” or “great” shape. Look, we’re all adults here. We don’t fool with silly metrics like how much we bench or squat. That’s silly. We need to be measuring the things that truly indicate our body’s performance ability. There’s no greater one than Vo2 Max. So how do we improve our Vo2 Max? First, a funny story.