# Cora

> a persistent health and fitness operating system for all your wearable data

Cora is a persistent, AI-native health and fitness operating system that reads wearable data (Apple Watch, Whoop, Garmin, Oura, Fitbit) and reasons across recovery, training, nutrition, and long-term history. Built by PurplePill AI, Inc. (Y Combinator W24). Not a "better X" — a new category: intelligence that synthesizes all your data to decide what you should do next.

## Top guides

- [VO2 Max by Age Chart](https://www.corahealth.app/blog/vo2-max-by-age): Complete VO2 max norms for men and women by age and fitness level
- [HRV Chart by Age](https://www.corahealth.app/blog/hrv-chart-by-age): Normal HRV (RMSSD) ranges by age with interpretation guidance
- [Best Apple Watch Fitness Apps](https://www.corahealth.app/blog/best-apple-watch-fitness-apps): Tested comparison of workout, recovery, and nutrition apps for Apple Watch
- [Best Recovery Apps](https://www.corahealth.app/blog/best-recovery-apps): Recovery app comparison across Apple Watch, Garmin, and Whoop
- [Best Workout Tracker (Reddit)](https://www.corahealth.app/blog/best-workout-tracker-reddit): Community-sourced comparison of workout tracking apps
- [Zone 2 Training Benefits](https://www.corahealth.app/blog/zone-2-training-benefits): Why zone 2 cardio matters for longevity and endurance
- [What Is HRV](https://www.corahealth.app/blog/what-is-hrv): Heart rate variability explained with practical applications
- [Progressive Overload Guide](https://www.corahealth.app/blog/progressive-overload): Six types of overload with implementation and tracking

## Tools

- [VO2 Max Calculator](https://www.corahealth.app/tools/vo2-max-calculator): Estimate with age/sex percentile and fitness age
- [Body Fat Calculator](https://www.corahealth.app/tools/body-fat-calculator): Navy, Bailey skinfold, BMI, and waist-to-height methods
- [Heart Rate Zone Calculator](https://www.corahealth.app/tools/heart-rate-zones): Personalized 5-zone heart rate targets
- [Resting Heart Rate Evaluator](https://www.corahealth.app/tools/resting-heart-rate): RHR percentile by age and sex
- [Workout Quiz](https://www.corahealth.app/tools/workout-quiz): Program recommendation by goals and schedule
- [Recovery Readiness Calculator](https://www.corahealth.app/tools/recovery-calculator): Train / easy / rest from sleep and HRV
- [Macro Calculator](https://www.corahealth.app/tools/macro-calculator): Daily calorie and macro targets

## Compare

- [Whoop Review (2026)](https://www.corahealth.app/compare/whoop-alternative): Subscription wearable — strain scoring and who it's for
- [Oura Ring Review (2026)](https://www.corahealth.app/compare/oura-alternative): Sleep tracking and readiness score
- [Garmin Connect Review (2026)](https://www.corahealth.app/compare/garmin-connect-alternative): Endurance fitness tracking and training status
- [Apple Fitness+ Review (2026)](https://www.corahealth.app/compare/apple-fitness): Studio workout classes
- [Athlytic Review (2026)](https://www.corahealth.app/compare/athlytic): Apple Watch recovery scoring
- [Fitbod Review (2026)](https://www.corahealth.app/compare/fitbod): AI-generated strength workouts
- [MyFitnessPal Review (2026)](https://www.corahealth.app/compare/myfitnesspal): Calorie and macro tracking
- [Compare Hub](https://www.corahealth.app/compare): Full list of fitness app and wearable editorial reviews

## App

- [Download Cora](https://www.corahealth.app/app): iOS app overview and download
- [App Store](https://apps.apple.com/us/app/cora-ai-fitness-coach/id6741827384): Cora on the Apple App Store (rated 4.8/5, 110+ ratings)
- [Y Combinator Profile](https://www.ycombinator.com/companies/cora): PurplePill AI — YC W24

## Apple Watch Health Metrics Reference

- [Apple Watch Fitness Metrics: Complete Guide](https://www.corahealth.app/blog/apple-watch-fitness-metrics-complete-guide): Hub page covering all 10 Apple Watch health metrics — HRV, VO2 max, resting heart rate, sleep stages, active calories, exercise minutes, wrist temperature, mindful minutes, and activity rings — with population benchmarks and links to dedicated reference pages

- [HRV by Age on Apple Watch](https://www.corahealth.app/blog/hrv-by-age-apple-watch): The average HRV (SDNN) on Apple Watch is 50–70 ms in your 20s–30s, declining to 28–45 ms in your 50s–60s; explains why SDNN runs higher than RMSSD and how to use your number as a recovery signal
- [VO2 Max on Apple Watch by Age](https://www.corahealth.app/blog/vo2-max-apple-watch-by-age): The average Cardio Fitness reading on Apple Watch is 40–44 mL/kg/min for men and 35–38 mL/kg/min for women in their 30s, mapped against Apple's four tiers (Low / Below Average / Above Average / High) and ACSM clinical categories
- [Resting Heart Rate on Apple Watch by Age](https://www.corahealth.app/blog/resting-heart-rate-apple-watch-by-age): The average RHR on Apple Watch is 65–72 bpm in your 20s–30s, declining to 62–68 bpm in your 40s–50s; covers how Apple Watch measures RHR vs. sleeping heart rate and how to use trends for recovery tracking
- [Apple Watch Cardio Fitness Explained](https://www.corahealth.app/blog/cardio-fitness-apple-watch-explained): What Apple's four Cardio Fitness tiers mean physiologically, how they relate to ACSM clinical VO2 max categories, and what training moves you between tiers
- [Sleep Stages on Apple Watch Norms](https://www.corahealth.app/blog/sleep-stages-apple-watch-norms): Normal adult sleep stage distribution on Apple Watch is roughly 20–25% REM, 45–55% Core, and 13–23% Deep; explains how distributions shift with age and how staging accuracy compares to polysomnography
- [Active Calories on Apple Watch by Age](https://www.corahealth.app/blog/active-calories-apple-watch-by-age): Active Apple Watch users average 400–650 kcal/day in their 20s–30s and 300–520 kcal/day in their 50s–60s; explains what the Move ring actually measures and how accuracy compares to metabolic testing
- [Exercise Minutes on Apple Watch Benchmarks](https://www.corahealth.app/blog/exercise-minutes-apple-watch-benchmarks): Apple Watch users who meet weekly guidelines average 35–50 Exercise minutes on active days; covers what counts toward the Exercise ring, WHO recommendation alignment, and benchmarks by age
- [Wrist Temperature on Apple Watch Norms](https://www.corahealth.app/blog/wrist-temperature-apple-watch-norms): Apple Watch Series 8 and later measures nightly wrist temperature deviation from your personal baseline; normal overnight variation is ±0.5°C and deviations beyond ±1°C signal illness, hormonal changes, or elevated training stress
- [Mindful Minutes on Apple Watch Benchmarks](https://www.corahealth.app/blog/mindful-minutes-apple-watch-benchmarks): Typical Apple Watch Mindfulness users log 5–12 mindful minutes per day; research suggests 10–20 minutes daily for measurable HRV and stress benefits via the Breathe app's resonance frequency breathing
- [Apple Watch Activity Rings Population Data](https://www.corahealth.app/blog/move-stand-rings-population-data): Fewer than 20% of Apple Watch users close all three rings on any given day; covers Move, Exercise, and Stand ring population completion rates from the Apple Heart and Movement Study and the health research on what consistent closure predicts
- [Calories Burned by Age](https://www.corahealth.app/blog/calories-burned-by-age): How many calories people burn per day by age and sex, with reference ranges for both total daily energy expenditure and active calories tracked by Apple Watch

## Apple Watch Coaching Guides

- [How to Improve HRV on Apple Watch](https://www.corahealth.app/blog/how-to-improve-hrv-apple-watch): Five evidence-based interventions — Zone 2 cardio, sleep consistency, biofeedback breathing, alcohol reduction, and stress management — that raise Apple Watch SDNN, with realistic improvement timelines
- [How to Improve Cardio Fitness on Apple Watch](https://www.corahealth.app/blog/how-to-improve-cardio-fitness-apple-watch): Zone 2 training, HIIT, and recovery management protocols that raise Apple Watch Cardio Fitness tier, with evidence-based timelines showing most people shift tiers within 3–6 months
- [How to Lower Resting Heart Rate on Apple Watch](https://www.corahealth.app/blog/how-to-improve-resting-heart-rate-apple-watch): Aerobic training, sleep improvement, and alcohol reduction lower Apple Watch resting heart rate by 5–10 bpm within 4–12 weeks, with intervention-specific evidence and timelines
- [How to Improve Sleep on Apple Watch](https://www.corahealth.app/blog/how-to-improve-sleep-on-apple-watch): Five evidence-based interventions — sleep timing consistency, alcohol elimination, room temperature, light management, and caffeine cutoff — that visibly improve Apple Watch sleep stage data
- [How to Close Apple Watch Rings Consistently](https://www.corahealth.app/blog/how-to-close-apple-watch-rings-consistently): Behavioral science framework for consistent ring closure: calibrated Move goals, fixed daily exercise anchors, and the never-miss-twice rule, with ring-by-ring strategies

## Optional

- [Blog](https://www.corahealth.app/blog): Full article archive — training, recovery, nutrition, wearables
- [Exercise Library](https://www.corahealth.app/exercises): 900+ exercises with form instructions and muscle filters
- [Privacy Policy](https://www.corahealth.app/privacy)
- [Terms of Service](https://www.corahealth.app/terms)