Vitals
What your blood pressure, heart rate, oxygen, and other vital signs mean, and how to measure them at home.
Nutrition
The National Academies' 2,300 mg a day for sodium and the WHO's 2,000 mg, the Adequate Intakes for potassium, how salt and sodium differ, and where most sodium in a diet comes from.
November 4, 2026 · 2 min read
Why 220 minus your age is only a rough guess, the Tanaka formula, how guidelines turn a maximum into moderate and vigorous zones, and how to find your own maximum.
November 4, 2026 · 3 min read
What a spirometry test measures, why results are compared with the lower limit of normal rather than a fixed percentage, the 0.70 ratio used for COPD, and how to compare tests over time.
November 4, 2026 · 3 min read
What a peak flow meter measures, how to find your personal best, the green, yellow, and red zones of an asthma action plan, and how reliever use fits beside it.
November 4, 2026 · 3 min read
Two numbers hidden in every blood pressure reading. How each is worked out, why a cuff's own mean arterial pressure differs from the formula's, and what a wide pulse pressure can mean.
November 4, 2026 · 3 min read
What a CGM shows in people without diabetes, the diagnostic thresholds for fasting and two hours after glucose, why a spike after a meal isn't a diagnosis, and how to read your own curves.
November 4, 2026 · 3 min read
What a single-lead watch ECG records, what its classifications mean, what the Apple Heart Study found about irregular rhythm alerts, and why it can't detect a heart attack.
November 4, 2026 · 3 min read
Menstrual Cycle
How progesterone raises your waking temperature after ovulation, why the rise confirms ovulation only after it's happened, how to take a reading that's comparable, and how it compares with a wearable's wrist temperature.
November 4, 2026 · 2 min read
What a beta-hydroxybutyrate meter measures, the levels seen with fasting and low-carbohydrate diets, the 3.0 mmol/L threshold for diabetic ketoacidosis, and when a reading is an emergency.
November 4, 2026 · 3 min read
Why watches and rings report temperature as a change from your own baseline, what moves it, how it follows the menstrual cycle and illness, and why it isn't a thermometer.
November 4, 2026 · 3 min read
For people with atrial fibrillation, the share of time spent in it. What the evidence links it to, how a watch estimates it, and what it can't tell you.
November 4, 2026 · 3 min read
How far your heart rate falls in the minute after hard exercise, the 12 bpm threshold from the landmark study, what moves it, and how to measure it the same way each time.
November 4, 2026 · 3 min read
How fast each heartbeat's pressure wave travels, why stiffer arteries make it faster, the 10 m/s threshold in European guidelines, and how a bathroom scale estimates it.
November 4, 2026 · 3 min read
Fitness
What maximal oxygen uptake measures, typical values by age and sex from the FRIEND registry, the evidence linking fitness to lifespan, and how to raise yours.
November 4, 2026 · 4 min read
Why 37 °C is an average rather than a rule, how mouth, ear, forehead, armpit, and rectal readings differ, what counts as a fever, and how to take a temperature you can compare.
November 4, 2026 · 3 min read
The 12 to 20 breaths a minute range, why a rising rate is one of the earliest signs of illness, how watches measure it overnight, and how to count it yourself.
November 4, 2026 · 3 min read
The WHO's 95% to 100% range, when a low reading is an emergency, what makes oximeters read wrong, including skin pigmentation, and how to take a reading you can rely on.
November 4, 2026 · 3 min read
A continuous glucose monitor measures the fluid under your skin, a meter measures blood. Why the two differ, especially when glucose is changing, how accurate each is allowed to be, and when to trust which.
November 4, 2026 · 3 min read
What systolic and diastolic pressure are, the categories doctors use, why one reading isn't a diagnosis, and when a number needs attention right away.
November 2, 2026 · 3 min read
The cuff, the arm, how you sit, and when you measure all change the number. Here's the method the American Heart Association recommends, step by step.
October 22, 2026 · 5 min read
The 60 to 100 bpm range, why your own normal matters more than anyone's average, what moves resting heart rate up and down, and how to follow it over months.
October 21, 2026 · 5 min read
What HRV measures, why SDNN and RMSSD give different numbers, and how to follow your own trend instead of comparing yourself with anyone else.
October 20, 2026 · 5 min read