There is a structural irony inside how most people relate to their own fitness data, and the healthcare and wellness industries are not built to fix it.
The people who care most about longevity, who buy the wearable, book the metabolic panel, do the occasional treadmill test, are often the ones with the least ability to see what any of it means over time. Because the number lives in one place, once.
And once is the same as nowhere.
VO2 max is the maximum rate at which your body can take in, transport, and use oxygen during intense exercise.
It is expressed in milliliters of oxygen per kilogram of body weight per minute, or in METs, where one MET is roughly 3.5 mL/kg/min. Gold standard testing uses a cardiopulmonary exercise test on a treadmill or bike, with a mask measuring gas exchange directly. Most people now encounter an estimate instead, generated by a wearable from heart rate and pace data, which is less precise but still directionally useful.
Typical untrained adults sit somewhere around 30 to 40 mL/kg/min. Well trained recreational athletes tend to land in the mid 40s to mid 50s. Elite endurance athletes can exceed 70, occasionally 80 or more. The number is shaped by genetics, sex, age, and training history, and genetics alone is estimated to account for close to half the variance between individuals. The other half is trainable.
That trainability has a shelf life problem built into it. VO2 max declines with age at roughly 5 to 15 percent per decade after the early thirties in people who do not train specifically to counter it, and the decline accelerates past 50. Structured training slows or reverses that curve. Zone 2 work, sustained effort at a pace where conversation is still possible, builds the aerobic base and mitochondrial density that underlie the number. Higher intensity interval work adds gains on top of that base, often producing measurable improvement within 8 to 12 weeks of consistent training, which is also the minimum window in which a real adaptation becomes distinguishable from ordinary test to test variation.
This is why VO2 max functions as a longevity marker and not just a fitness one. A large Cleveland Clinic cohort of more than 122,000 people, followed for over a decade, found that those with low cardiorespiratory fitness carried roughly five times the mortality risk of elite performers, a larger gap than smoking, diabetes, or hypertension produced in the same population. Few numbers in medicine carry that kind of signal.
What the data actually shows:
Each 1 MET increase was associated with a 13 percent lower risk of all-cause mortality and a 15 percent lower risk of coronary heart disease and cardiovascular events (Kodama et al., JAMA 2009).
The lowest fitness quartile carried close to a 500 percent higher mortality risk than the highest, a wider gap than any single traditional risk factor produced in the same cohort.
No upper limit was observed. Risk kept declining as fitness improved, even past ranges typically considered elite.
A meaningful training response is generally visible within 8 to 12 weeks, and untrained decline runs at roughly 5 to 15 percent per decade after the early thirties without targeted work.
None of this is useful from a single number, though. A VO2 max of 42 means very different things depending on whether it followed two years of consistent zone 2 training or a quiet decline since an injury changed how much someone moves. The reading is information. The direction it has been moving is the actual story, and that direction only becomes visible when the same metric is measured the same way, repeatedly, on one timeline.
This is what Octo is trying to fix. Not the treadmill test, not the wearable estimate, but the infrastructure that lets last year’s number sit next to this morning’s, with the direction between them visible at a glance, alongside resting heart rate, HRV, and grip strength on the same timeline.
Lifespan is how long you live. Healthspan is how long you live well, and cardiorespiratory fitness is one of the clearest levers anyone has over it. Protecting that lever is largely the practice of watching the number closely enough, and continuously enough, to catch the drift before it becomes a decade of it.
One reading is a rumor. The trend is the truth.
One Timeline. Every Result.
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