What Is a Longevity Score? How Clinics Measure Fitness Age and Biological Age

This article is for educational purposes only. Nothing here constitutes a medical diagnosis. All bio-age and longevity-score values are estimated and non-diagnostic.

"Biological age" (Estimated · Non-diagnostic) and "longevity score" are now appearing on clinic menus across the UK, Europe and the US — but what do they actually measure, what inputs go into them, and how can software calculate them responsibly? This article explains the science, the standard inputs, and how Aerivity automates the calculation while staying honest about its limits.

Chronological age vs biological age vs fitness age

Three terms get used interchangeably. They shouldn't be.

• Chronological age — time since birth. Fixed.
• Fitness age — cardiorespiratory fitness expressed relative to a peer reference. A 50-year-old with the VO₂ max of an average 35-year-old has a fitness age of ~35.
• Biological age (Estimated · Non-diagnostic) — a multi-biomarker composite estimate of physiological age. Inputs may include blood panels, HRV, epigenetic methylation, telomere length and cardiorespiratory fitness.

Most clinics actually report a fitness age and label it as biological age. That's a meaningful number — but the language should match the data.

What inputs go into a longevity score?

A defensible longevity score is built from physiological inputs with the strongest published links to all-cause mortality:

• VO₂ max — the single strongest predictor of all-cause mortality in adults.
• Heart rate recovery at 1 and 2 minutes — a vagal-tone marker linked to cardiovascular mortality (Cole et al., NEJM 1999).
• Resting metabolic rate — context for body composition and metabolic health.
• Fat oxidation rate — metabolic flexibility, a marker of substrate handling.
• Lactate threshold (VT1 / VT2) — submaximal capacity and training status.
• Optional: blood biomarkers, HRV, sleep data — if the clinic offers them.

How VO₂ max predicts lifespan

Multiple large cohort studies — including Mandsager & Kokkinos et al. (JAMA Network Open, 2018) and Myers et al. (NEJM, 2002) — have shown VO₂ max to be the strongest single predictor of all-cause mortality in adult populations, often outperforming established risk factors such as hypertension, smoking and diabetes. The relationship is dose-dependent: each additional MET of cardiorespiratory fitness is associated with a meaningful reduction in mortality risk over follow-up periods of 8–15 years.

That's why VO₂ max sits at the heart of any credible longevity score. It is the single data point most likely to change a client's behaviour — and the one most worth measuring accurately.

Mortality risk by cardiorespiratory fitness category

Adapted from Mandsager et al. (2018), the chart below shows adjusted hazard ratios for all-cause mortality across cardiorespiratory fitness percentile bands, relative to the elite (>97.7th percentile) reference group.

How Aerivity calculates longevity score

Aerivity's scoring engine is intentionally transparent. The score is a weighted composite of VO₂ peak, HR recovery (1 and 2 min) and RMR, normalised against age- and sex-matched reference data drawn from the ACSM Guidelines. Every report includes an "Explain Score" panel that breaks down each component and the weight applied — so a clinician can answer client questions, and a skeptical client can see the maths.

The output is always labelled "Estimated · Proprietary · Non-diagnostic". Biological age (Estimated · Non-diagnostic) is presented as a derived estimate, not a clinical diagnosis. This matters: clinics that over-claim on bio-age create regulatory exposure and erode trust the first time a sophisticated client asks where the number came from.

Limitations and ethical considerations

Longevity scoring is genuinely useful and genuinely overhyped. Clinicians who deploy it should be honest about its limits:

• It's epidemiological, not deterministic. A 5× hazard ratio at the population level does not translate to a personal prophecy. Individual outcomes vary enormously.
• Composite scores hide their assumptions. Two clinics with different weightings will return different "ages" from identical inputs. Always publish the formula.
• Bio-age ≠ fitness age. Calling a cardiorespiratory composite a "biological age" overstates the model. Use accurate language in reports.
• Single-test bias. A bad night's sleep, dehydration or sub-maximal effort can shift VO₂ peak by 5–10%. Communicate the confidence interval.
• Equity of reference data. ACSM normative tables under-represent some demographics. Be transparent when interpreting outside well-sampled populations.

Fitness age vs biological age — what clinics should say

Responsible language matters. We recommend:

• Use "Fitness Age (Estimated)" when the score is calculated from cardiorespiratory data alone.
• Use "Biological Age (Estimated · Non-diagnostic)" only when additional biomarker inputs are present.
• Always include a one-line disclaimer in the report: "Estimated value for informational purposes; not a medical diagnosis."
• Never present the number as a hard clinical figure or a prognosis.

Aerivity defaults to this language across every template. Clinics can override the wording per template, but the disclaimer cannot be removed from the report footer.

Communicating scores to clients

How you frame the score is at least as important as the score itself. A few patterns we recommend after working with hundreds of clinic deliveries:

• Lead with the percentile band, not the number. "You're in the 78th percentile for men aged 40–49" is more actionable than "Your VO₂ is 47.2".
• Anchor the conversation in change, not absolutes. Bring up the previous test side-by-side; show the delta and the percentile movement.
• Tie every number to an intervention. A weekly Zone 2 prescription, a VT2 interval block, a strength minimum. Numbers without next steps demotivate.
• Schedule the retest in the same conversation. Twelve weeks is the minimum window in which cardiorespiratory change is measurable; bake it into the renewal plan.

More on bio-age scoring

Aerivity is a brand of Xharvoc Ltd, the UK-registered parent company behind the platform. The product page covers how the transparent longevity score, ACSM percentile breakdown and clinician override controls are presented to clients. Longer-form articles on bio-age methodology, VO₂ max interpretation and longevity testing are published on the Aerivity blog on xharvoc.co.uk.