How to Understand Your Fitness Tracker Data With AI

Most wrist wearables measure heart activity with photoplethysmography (PPG). Green LEDs shine into the skin, and a sensor detects changes in reflected light as blood volume pulses. From that signal the device derives heart rate and heart rate variability. Combined with motion and GPS data, it also produces estimates such as VO2 max. Heart rate variability (HRV) is the variation in time between consecutive heartbeats. Higher values generally reflect more parasympathetic, or rest-and-digest, activity. But HRV is highly individual: 35 milliseconds can be normal for one person and low for another. Brands also use different measures. Oura, WHOOP and Garmin generally report RMSSD, often measured during sleep, while Apple Health reports SDNN, so the numbers are not comparable across brands. Alcohol, illness, poor sleep, hard training and stress can all lower HRV for one night or several. Resting heart rate is steadier and easier to interpret. The American Heart Association describes 60 to 100 beats per minute as the typical adult range, and fit people often sit lower. A sustained rise of several beats above your baseline can accompany illness, overtraining or poor sleep. A watch's VO2 max is an estimate based on the relationship between heart rate and pace. It is not a lab measurement taken with a mask. It is useful for long-term direction and less useful as an exact value. Steps are the simplest metric. The 10,000-step goal traces back to 1960s Japanese pedometer marketing, not a clinical trial. Research suggests health benefits rise with step count and level off below 10,000 for many older adults. The key misconception is that one reading means something. The signal is in trends against your own baseline. Wearables also do not diagnose anything. Symptoms such as chest pain or fainting need a clinician, not a data review.