The method
How the Index is measured
Every number in your score comes from a published study. Here are all of them — what each one measured, how many people it followed, and where its evidence stops.
The scale
Your score is your percentile.
If you score 68, you performed better than 68 per cent of people your age and sex. Fifty is average. It is that simple, and it is deliberate.
Fixed thresholds — the kind that say everyone should manage a certain number whatever their age — over-identify older adults as failing and let younger ones off. Scoring against your own age group is what the authors of the largest normative dataset we use recommend, and this is that recommendation implemented.
But average is not where we draw the line. Scoring 50 means declining at the same rate as everyone else your age. That is ageing on schedule rather than holding your ground, so Holding begins at 55: you have to beat typical to reach it.
The consequence follows, and it is better said here than discovered on your own result: scoring 50 puts you in Slipping, and roughly six in ten people land in Slipping or Reversing. That is not a fault in the scale. It is what the population data shows, and it is the whole point of measuring rather than guessing.
Any one domain below 40 holds the Index at 54. A domain in Reversing means you cannot be better than Slipping overall, however strong the arithmetic elsewhere — a good heart does not buy back a floor you cannot get up from.
Failing the ten-second balance stand holds it at 39, but only between the ages of 51 and 75. That is the range the study validated, and outside it a failure is reported without a cap. Where either cap applies, the report states the uncapped figure and which domain was responsible.
The range
Why there is a range next to your number.
Every measurement carries error. A tape measure has less than an estimate of body composition; a laboratory VO₂ max test has less than a calculation from your resting heart rate.
Rather than hide that, we add it up and print it. 68, give or take 6 means the honest answer is somewhere in that range. The more of your data comes from real instruments, the narrower it gets — and a change smaller than the range is not a change, which is why the protocol asks for twelve weeks between tests.
The tests
What each one predicts.
Cardiorespiratory
The strongest single predictor of mortality we measure. Scored against the FRIEND registry, which holds maximal treadmill tests verified by gas analysis. Where you have not had a laboratory test, it is estimated from age, sex, body mass index, resting heart rate and training habit.
The estimate carries a standard error of about 5 ml/kg/min — roughly a sixth of the whole range from the 5th to the 95th percentile. Scoring an estimate rather than a measurement widens the error around your whole Index, and the report says by how much rather than quietly absorbing it. A measured test narrows your Index more than any other single number you can add.
How fast your heart rate falls in the minute after exercise. Recovery below twelve beats carried a relative risk of 4 for death in the original study, and was confirmed in 19,551 people with no cardiovascular disease followed for twelve years.
It discriminates hardest in people who are unfit to begin with. If your cardiorespiratory fitness is already normal it tells you less, and it is weighted accordingly — 30 per cent of the domain against the estimate's 70.
There is no published table of recovery by age and sex anywhere, so the score beside the flag is read against a single older cohort and reads high for most people here. It counts, and it is marked provisional wherever it appears.
Strength and tissue
The best-evidenced measurement in the battery. Across 139,691 people in seventeen countries, every 5 kg of lost grip carried a 16 per cent higher risk of death — a stronger predictor than systolic blood pressure. Scored against British centiles drawn from 49,964 people aged 4 to 90.
Stand and sit as many times as you can in sixty seconds. Reference values come from a Swiss population study of 6,926 adults.
No values exist above age 79. More than a fifth of over-80s could not complete the test, so the authors declined to publish percentiles for them, and neither do we — over-79s return unscored on this test rather than being given a number.
Upper-body pushing strength, and lateral trunk endurance. The side plank is scored on the difference between your two sides rather than how long you hold: an asymmetry needs no reference population, because you are compared against yourself.
There is no published percentile table for press-ups covering both sexes across the adult range. The band table this test used to carry was extrapolated from a study of 1,104 men and has been withdrawn, so your count is recorded, shown, and contributes nothing to your Index until real percentiles exist.
Where you have them. Relative muscle power is a notably strong predictor: comparing the lowest quarter with the highest gave hazard ratios of 5.88 in men and 6.90 in women, where the same analysis for strength was not statistically significant. Power matters more than most people training for strength assume.
Movement
Sitting down to the floor and standing back up, scored on how much support you needed. Followed in 4,282 adults for a median of twelve years: the lowest scoring group had a natural-cause mortality hazard ratio of 3.84 against the highest. Death rates ran from 3.7 per cent among those scoring a perfect 10 to 42.1 per cent among those scoring four or below.
Standing on one leg. In 1,702 adults followed for a median of seven years, those who could not hold ten seconds had an adjusted mortality hazard ratio of 1.84. One in five could not.
That study covered ages 51 to 75 and nobody younger, so below 51 the ten-second test says very little either way. It is also observational: poor balance and earlier death travel together, which is not the same as one causing the other.
Eyes open, the test ceilings badly in midlife — around seven in ten 53-year-olds hold it for the full thirty seconds, so it separates almost nobody. The eyes-closed version is the one that discriminates under sixty, and it is scored against 7,658 English adults aged 50 to 69 and nobody outside that range.
The sources
Every study, and how many people.
Fourteen studies. If a figure appears anywhere in your report, it came from one of these.
| Study | What it gave us | People |
|---|---|---|
| PURELeong et al, The Lancet, 2015 | Grip and mortality | 139,691 |
| Twelve British studiesDodds et al, PLOS ONE, 2014 | Grip centiles, ages 4–90 | 49,964 |
| Non-exercise fitness modelJurca et al, Am J Prev Med, 2005 | VO₂ max estimate | 38,137 |
| Canadian Longitudinal Study on AgeingMayhew et al, Age & Ageing, 2023 | Chair rise, grip, balance | 25,470 |
| Mayo primary prevention cohortSydó et al, JAHA, 2018 | Heart rate recovery | 19,551 |
| Muscle power reference valuesAlcazar et al, 2021 | Lower-body power | 9,906 |
| FRIEND registryKaminsky et al, Mayo Clin Proc, 2015 | Measured VO₂ max percentiles | 7,783 |
| English Longitudinal Study of AgeingGrgic et al, GeroScience, 2026 | Balance and chair rise, English | 7,658 |
| Swiss population studyStrassmann et al, Int J Public Health, 2013 | One-minute sit-to-stand | 6,926 |
| Sit-rise reference scoresAraújo et al, Eur J Prev Cardiol, 2020 | Sit-rise norms, ages 16–98 | 6,141 |
| Sit-rise mortality follow-upAraújo et al, 2025 | Twelve-year outcomes | 4,282 |
| Cleveland Clinic cohortCole et al, NEJM, 1999 | Heart rate recovery threshold | 2,428 |
| Balance and survivalAraújo et al, BJSM, 2022 | Ten-second stand | 1,702 |
| Firefighter cohortYang et al, JAMA Netw Open, 2019 | Press-ups and cardiovascular events | 1,104 |
| Total | 320,743 | |
Some reference values are drawn from our own cohort, tested under the same protocols in London. Those are marked on your report wherever they apply, and they are marked provisional until the cohort is large enough to publish.
The limits
What we cannot tell you.
The Index measures physical capability against people your age. It is not a medical test, it does not diagnose anything, and it cannot tell you how long you will live.
What the studies above show is that people who perform poorly on these measurements die earlier, on average, across large populations. That is a statement about populations and not about you. A high score is not a guarantee and a low one is not a sentence — and every one of these measurements is trainable, which is rather the point of measuring them.
If a measurement has no reference data for someone your age, we do not score it and we do not guess. You will see that stated on your own report rather than buried here.
Where to start
Your number, and what it costs.
The Provisional Index is free. You enter your own measurements and get the score, the Capacity Age and the report with nothing to buy — create your account on that page and it is kept, along with everything you add later.
A certified Index is measured by the Evolution team at Grosvenor Square on calibrated equipment. The two are not the same thing, and a self-measured result says so on its own face: it carries the wider error of self-measurement, and the report prints that error rather than hiding it.