Digital health is the intersection of digital technology (sensors, AI, mobile internet) and healthcare, centered on using continuously generated personal health data to achieve early disease detection, personalized prevention, and chronic disease management. From FDA approval of Apple Watch for atrial fibrillation detection to CGM enabling real-time blood glucose monitoring for diabetics, digital health is reshaping the patient-physician relationship and disease management paradigm. The global digital health market is approximately $350 billion in 2024, projected to exceed $800 billion by 2030.
## Major Wearable Device Categories and Core Metrics
**Smartwatches**: Apple Watch, Samsung Galaxy Watch, Garmin, and others. Core health functions: optical heart rate monitoring (PPG, photoplethysmography), ECG (single-lead), blood oxygen saturation (SpO₂), skin temperature, activity detection, and fall detection. Apple Watch studies show approximately 84% sensitivity and ~99% specificity for atrial fibrillation (AFib) detection — though AFib’s intermittent nature means miss rates remain significant.
**Advanced health trackers**: Oura Ring (ring form factor, sleep analysis core), WHOOP (recovery state monitoring focus), Garmin Fenix series (athlete-oriented). Oura Ring’s sleep staging algorithm shows approximately 70-80% accuracy vs. polysomnography (PSG gold standard); its HRV and RHR measurements are considered among the most accurate consumer products.
**Continuous Glucose Monitoring (CGM)**: Abbott FreeStyle Libre, Dexterity, domestic Chinese brands. CGM use in non-diabetic populations (“preventive CGM”) has grown in Silicon Valley biohacker circles, helping understand individual blood glucose response variation (e.g., white rice vs. brown rice; pre-meal vs. post-meal exercise effects on glucose curves).
## Correct Interpretation of Health Data
**HRV (Heart Rate Variability)**: the variation in time between consecutive heartbeats, reflecting autonomic nervous system balance (parasympathetic/sympathetic ratio). High HRV → good recovery, parasympathetic dominance; low HRV → stress, fatigue, or pre-illness signal. But HRV individual variation is enormous (absolute values cannot be compared across people); focus on personal baseline fluctuations rather than comparing with others. HRV is most accurately measured in the morning (lying supine, 5 minutes of rest).
**Resting Heart Rate (RHR)**: long-term regular aerobic exercisers’ RHR can fall to 40-50 bpm (athlete’s heart); normal adults approximately 60-80 bpm. improve RHR (more than 5 bpm above personal baseline) typically indicates inadequate recovery, sleep deprivation, or impending illness.
See [Sleep Health Science](https://sunqi.org/sleep-health-science-en/) and [Apple Watch health features official page](https://www.apple.com/apple-watch/health/).
