Learn
Evidence-based guides on VO2 Max, Resting Heart Rate, cardio fitness, and what your Apple Watch health data actually means.
VO2 Max by Age and Gender
Percentile charts for men and women, what Apple Watch measures, and how to improve your score.
VO2 Max Percentile Calculator
Enter your age, sex, and VO2 Max to see how your cardio fitness compares to others your age.
Cardio Fitness Level Checker
Enter your VO2 Max, age, and sex to see your Apple Watch cardio fitness classification and what it means for your health.
Resting Heart Rate by Age
Normal ranges by age and fitness level, what affects your RHR, and why athletes trend lower.
Apple Watch Resting Heart Rate: What Your Trends Mean
Your resting heart rate went up. Here's what rising, falling, and spiking trends mean — and when your Apple Watch is telling you something important.
Resting Heart Rate Percentile Calculator
Enter your age, sex, and resting heart rate to see how your cardiovascular fitness compares to others.
How to Improve Your VO2 Max
The training methods, timelines, and daily habits that drive real cardio fitness gains.
Apple Watch VO2 Max Accuracy
What the research says, how it compares to lab tests and Garmin, and why your reading might be off.
How Often Does Apple Watch Update VO2 Max?
Apple Watch doesn't update VO2 Max on a schedule. Here's what triggers a new reading, why yours stopped updating, and how to get more frequent estimates.
Why Did My Apple Watch VO2 Max Drop?
Your VO2 Max dropped and you didn't change anything. Here are 7 real reasons — from cooldown walks to software updates — and what to do about each one.
What Is Cardio Fitness?
What it measures, why it matters for longevity, and how to check your level on Apple Watch.
What Is a Normal Resting Heart Rate?
The healthy range, what affects your number, how to measure it, and when to be concerned.
How to Lower Your Resting Heart Rate
The most effective methods, realistic timelines, and the daily habits that make the biggest difference.
Resting Heart Rate While Sleeping
How sleeping heart rate differs from daytime resting rate, what is normal by age, and what disrupts it.
VO2 Max and Longevity
The research behind cardio fitness and mortality, and why it predicts how long you live.
Apple Watch Cardio Fitness Below Average
Why your reading might be wrong, what it means if accurate, and exactly how to improve it.
How Sleep Affects Your Heart Rate
The direct connection between sleep quality, resting heart rate, and cardiovascular fitness.
Does Sleep Really Affect Your VO2 Max?
Research shows sleep quality accounts for up to 20% of VO2 Max variance. Here's the science, the mechanisms, and what to do about it.
Improve VO2 Max Without Running
The best non-running activities for cardio fitness, ranked by effectiveness.