Most longevity tools hand you a number from a questionnaire. This one reads it off a hike.
Your trail-derived biological age estimates how old your body performs — not how old it is — built from the single strongest predictor of healthspan: VO₂max, estimated here from your grade-adjusted effort against your heart-rate reserve.
That fitness signal is then age-graded against population reference curves and pooled with two autonomic markers — resting heart rate and heart-rate variability.
The pooling is the honest part. A strong aerobic engine alone reads absurdly young, so your autonomic markers pull the estimate back toward what your whole system actually supports — and the model isn't theoretical. It's calibrated on 25 instrumented World Model sessions and tuned until it reproduced a known, published result.
Enter one representative hike below to see your own, then put the number to work with the VO₂max Playbook.