- Apr. 15th 2022 2:35 pm PT

Beyond Apple Watch’s ability to track basic activities like steps and exercise, more sophisticated features like ECG, high/low heart rate warnings, and fall detection offer a lot of value and have gained mainstream attention. But flying under the radar, Apple Watch has several lesser-known important capabilities that measure everything from current to future overall health, likelihood of mortality, and your base metabolic rate. Let’s look at four hidden Apple Watch health features you’re probably not using.

Tracking VO2 max on Apple Watch is hidden for two reasons. First, even if you’re looking for the metric, it’s turned off by default and goes by a different name on watchOS/iOS: Cardio Fitness.

Secondly, once enabled, VO2 max/Cardio Fitness measurements are only recorded with Apple Watch during a brisk hike, walk, or outdoor run (specifically choosing those in the Apple Watch workout app).

Even though you’ll get VO2 max readings less often since it’s only measured for three workout types, it’s a very worthwhile feature to set up.

Along with helping to understand your cardiorespiratory fitness, research shows that VO2 max is a good indicator of overall health as well as predicting long-term health. Check out our full guide on setting up and using VO2 max:

What is VO2 max and why should you set it up with Apple Watch?

Heart rate variability (HRV) is automatically captured by Apple Watch but it’s not viewable in the wearable’s native Heart Rate app. To see it you’ll need to head to the iPhone’s Health app > Browse > Heart.

What is HRV? It’s the measurement of how the interval of time between heartbeats changes, measured in milliseconds – notably this is a metric that changes a lot, so looking at broad trends, not daily numbers is important.

HRV is considered by many in the medical field as a powerful indicator of not only current overall health and resilience of the heart and body but also a strong predictor of future mortality.

HRV is also often used as a signal to understand when the body is ready for exercise or rest. All of this is thanks to HRV showing how responsive the heart is to our autonomic nervous system.

What is HRV and how can you track/use it with Apple Watch and iPhone?

Heart rate recovery is a bit less hidden than HRV as it shows up on Apple Watch and iPhone automatically after tracking a workout.

But what does it mean? Like HRV, heart rate recovery can indicate heart health by how well it listens to the autonomic nervous system.

Studies have shown abnormally low heart rate recovery is a strong predictor of being 2x more likely to die within six years.

What is Apple Watch heart rate recovery? Here’s why it’s important and how to use it

Apple Watch prominently shows active calories burned but what about passive calories, also known as your base metabolic rate?

While Apple Watch tracks this, it’s not viewable on the wearable, you’ll need to head to the Health app on iPhone and do a little math.

Understanding your passive calorie burn/base metabolic rate is valuable as it can show you the impact of increasing muscle mass (more muscle = more passive calories burned). And of course, it’s also key to understanding how much to eat if you’re looking to be in a calorie deficit or calorie surplus.

And if you want to go further with understanding your metabolism in real-time, I recommend checking out Lumen’s pocket-sized metabolic analyzer (reviewed) that works with Apple Health.

Apple Watch: How to see calories burned – active, passive, and total

Have you been using some or all of these advanced Apple Watch features? Or excited to try them out? Share your ideas and experiences in the comments below!

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Apple Watch is Apple's wearable is designed to help you stay active, motivated, and connected. It runs watchOS, and it comes in 40mm and 44mm size options.

A collection of tutorials, tips, and tricks from the 9to5Mac team helping you fix and get the most out of your favorite gear.

Michael is an editor for 9to5Mac. Since joining in 2016 he has written more than 3,000 articles including breaking news, reviews, and detailed comparisons and tutorials.

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