Metrics Library

Welcome to the Scientific Metrics Library. This repository contains detailed, evidence-based deep dives into the health metrics tracked by Apple Health and modern wearable devices.

Note: All content is grounded in peer-reviewed clinical research (NEJM, Lancet, JAMA) and international consensus guidelines (WHO, AHA, IAS).

🏃 Running & Fitness Metrics Analytics

Quantifying activity volume and intensity. * Step Count (The 10k myth vs. Lancet mortality data) * Active Energy (Calories & Constrained Energy Model) * Flights Climbed (Vertical effort & cardiovascular health) * Distance Walking/Running (Stride length & volume) * Apple Exercise Time (The "Green Ring" & WHO vs. MVPA)

❤️ Cardiovascular & Vital Signs Monitoring

The engine of life. Vital signs and recovery metrics. * Resting Heart Rate (Cardiovascular efficiency) * Heart Rate Variability (HRV) (Stress, recovery & nervous system balance) * Blood Pressure (Hypertension & SPRINT trial targets) * ECG & Afib (Rhythm analysis & Apple Heart Study) * Heart Rate Recovery (Post-exercise autonomic function) * Walking Heart Rate Average (Proxy for aerobic fitness)

😴 Sleep & Recovery

Restoration, brain health, and metabolic reset. * Sleep Stages (Deep/REM functions & brain health) * Sleep Duration (The U-shaped mortality curve) * Respiratory Rate (The "forgotten vital sign") * Sleep Apnea Screening (Breathing disturbances & O2)

🫁 Respiratory & Vitals

Lung function and blood oxygenation. * VO2 Max (Cardio Fitness) (The strongest predictor of longevity) * Blood Oxygen (SpO2) (Hypoxemia & altitude acclimatization)

🚶 Mobility & Gait

Functional independence and fall risk. * Walking Steadiness (Fall risk prediction & TUG validation) * Gait Metrics (Asymmetry & walking speed) * Six-Minute Walk (Functional capacity standard)

⚖️ Body Composition & Weight Metrics

Composition over weight. Metabolic health markers. * Weight & BMI (Screening utility vs. inaccuracy) * Waist Circumference (Visceral fat & metabolic risk) * Body Fat % (Age-adjusted healthy ranges)

Last Updated: 2025