The strongest single predictor of all-cause mortality — aerobic fitness quantified.
VO2 max is the maximum volume of oxygen your body can use per minute per kilogram of body weight — the gold-standard measure of aerobic capacity. It's also the strongest single predictor of all-cause mortality in the epidemiological literature, stronger than smoking status, diabetes, or cholesterol profile.
Apple Watch estimates VO2 max from outdoor run/walk HR response via a proprietary algorithm. It's not as accurate as a lab-based graded exercise test but is very useful for trend tracking over months. Garmin uses a similar approach. Lab testing remains the definitive method.
VO2 max declines ~1% per year after age 30 without training. Training can maintain or even increase it substantially through the 40s and 50s. Hitting the top quartile for age is a meaningful longevity target.
VO2 max is influenced by: aerobic training volume and intensity (primary lever — zone 2 + interval work), genetics (meaningful individual ceiling variance), body composition (lower fat mass = higher normalized VO2 max), anemia (lowers it via oxygen carrying), hemoglobin, and age. Pharmacologic: GLP-1s typically improve it indirectly via weight loss; beta-blockers lower it during exercise by capping heart rate.
Track via Apple Watch / Garmin during regular outdoor cardio. Expect seasonal variation if training volume fluctuates. On GLP-1 therapy, VO2 max usually improves 10–15% at maintenance dose due to weight reduction. On GH protocols, subjective recovery often improves but VO2 max itself doesn't shift much. StackAI uses VO2 max trends as long-term aerobic-capacity signal.
Upload any lab PDF and MyProtocolStack maps your values to VO2 Max and 40+ other biomarkers. StackAI interprets the trend in context of your protocol.
Start tracking →Informational only — not medical advice. Reference ranges vary by lab and individual context. Work with a licensed provider to interpret your specific results.