Biometrics
The measurements that come off your body rather than out of a tube. What each one is, why it is worth following, and how to take it yourself.
Why these and not fifty others
Every measurement here answers to the same two questions. Does it predict something that matters, and can you do anything about it. A number that fails the first is a hobby; a number that fails the second is a diagnosis you cannot act on.
None of this is a diagnosis. A measurement you take at home is worth having and it is not a verdict, and the ones that need a doctor say so.
Strength and shape
Grip strength
Every 3 monthsHow hard you can squeeze, in kilograms. It reads as a proxy for your whole muscular system, which is why it predicts so broadly and explains so little on its own.
How to measure it A hand dynamometer, about twenty euros. Three squeezes per hand, take the best one, standing with your elbow at your side.
Waist
MonthlyThe circumference of your middle. It tracks the fat around your organs, which is the fat that moves your blood sugar and your triglycerides, and it does that better than your weight does.
How to measure it A tape measure, halfway between your lowest rib and your hip bone, at the end of a normal breath out. Same time of day each time.
Weight
WeeklyYour body weight. On its own it is the least informative number on this page, because it cannot tell muscle from fat from water.
How to measure it Scales, in the morning, after the toilet and before eating. Weekly, because daily weight is mostly water and reading it daily mostly produces frustration.
Height
OnceMeasured once, and then hardly ever again. It earns a place because several other figures are read against it.
How to measure it Against a wall, without shoes, heels together, looking straight ahead.
Heart and fitness
VO2max
Every 3 monthsHow much oxygen your body can use at full effort. Of everything on this page it is the strongest single predictor of how long you live, and it responds to training.
How to measure it A watch estimates it from your heart rate during a run. That estimate drifts, so follow your own line rather than comparing it to somebody else's. A laboratory test is the real thing.
Resting heart rate
WeeklyYour heart rate at complete rest. It falls as your fitness rises and climbs when you are ill, hungover, short of sleep or under strain.
How to measure it A ring or a watch measures it overnight, which is the cleanest moment. By hand: sixty seconds, lying still, before you get up.
Blood pressure
Every 3 monthsThe pressure in your arteries, upper over lower. It causes damage silently for years, which is exactly why it is worth a monitor at home.
How to measure it An upper-arm monitor, sitting, five minutes of quiet first, arm at heart height. Two readings a minute apart, note the second. Persistently high belongs with a doctor.
Sleep and recovery
Heart rate variability
WeeklyThe variation between one heartbeat and the next. More variation generally means a nervous system that is not braced. It differs enormously between people, so only your own baseline means anything.
How to measure it A ring or a chest strap, overnight. Compare it to your own average over the last fortnight and never to anybody else's number.
Sleep
DailyHow long you actually slept, which is not how long you were in bed.
How to measure it A ring or a watch estimates it. Without one, note the time you went to sleep and woke, and subtract a rough half hour.
Daily
Steps
DailyHow much you move without calling it training. It fills the twenty-three hours that a workout does not.
How to measure it Any phone or watch counts them. The number matters less than the direction it moves in.
Water
DailyHow much you drink. It is here because it is easy to track and easy to get wrong in both directions.
How to measure it Count glasses or fill a bottle you know the size of. Thirst and pale urine tell you more than any target does.
Breathing
DailyMinutes spent breathing deliberately. It is the one measurement here that is a practice rather than a property.
How to measure it A timer. Slow breathing, roughly ten breaths a minute or fewer, is what the trials tested.
And if the number comes off a wrist
Half of these are measurements people try to get from a tracker instead. Some of those numbers hold up against laboratory equipment and some are invented, which has been studied, and so has the other question: what a sensor strapped to one patch of skin around the clock is doing to it. That page says what we would pick per measurement and what we earn from saying it, which is nothing.
Where these get kept
Entering a value once tells you very little. The line it makes over a year is the whole point, which is what the hub is for.