What your wearable's numbers really mean, and what to do with them
Data2Fit
Data2Fit explains the numbers from fitness trackers, smartwatches and smart rings: what each metric measures, how accurate it is, and how to use it to train, recover and sleep better.
5min
Your watch estimates VO2 max from your heart rate at a known speed. Here is how Garmin, Apple and Fitbit do it, how close they get to a lab test, and what makes the number jump around.
5min
Your watch compares this week's training with your last four weeks. Here is how that load ratio is calculated, where its famous thresholds came from, why researchers now dispute it, and how to use it sensibly.
5min
Your watch or ring guesses sleep stages from movement and pulse, not brain waves. It is good at asleep versus awake and weak at one night’s deep and REM split. Here is what the research shows and which numbers to trust.
5min
Most watches build zones from an age-based maximum that can be off by ten beats or more. How the three zone methods differ, how Garmin and Apple Watch set them, and how to give your watch better numbers.
4min
The wrist sensor reads blood flow, a chest strap reads the heart's electrical signal. That is why the wrist is fine for rest and steady runs but lags in intervals, lifting and the cold.
5min
Wear it snug, on top of the wrist and a finger above the wrist bone, then move it higher and tighter for workouts. Here is why each step matters, and what fit cannot fix.
5min
HRV is the change in time between heartbeats. Here is how Oura, Whoop, Garmin, Fitbit and Apple Watch measure it, why their numbers can't be compared, how accurate they are, and how to read your own trend.
4min
Resting heart rate is one of the most reliable wearable numbers, but Oura, Apple Watch and Fitbit each define 'resting' differently. What it measures, how accurate it is, what raises it and when to see a doctor.
