Making sense of your wearable data

So you got yourself a cool wearable device for Christmas. Now you’re all set up, and eagerly tracking your steps trying to hit that 10K a day.

Is that it, then? Is the whole premise of these expensive, complex devices based on just counting steps? No, it isn’t. There’s a whole treasure trove of data these devices produce but don’t necessarily communicate that effectively.

So let’s delve in, and see what you can learn from your wearable data. For the purposes of this exercise, I’ll be focusing on some of the most popular devices on the market: Apple Watch, Fitbit, Garmin, and Oura Ring.

Disclaimer: I’m not a doctor, so don’t be a douche and assume this is some form of medical advice. If you’re confused or worried, ask your doctor. If you don’t have one, get one.

Where do I find the data?

Your first question might be, where is all this data going? Let me show you.

Apple Watch

The beauty of the Apple Watch is that it’s deeply integrated into the iOS system, and automatically stores all your data into the Activity and Health apps on your phone. The Health app is pretty cool because it’s a private database only you can access. Other apps that want to examine that data need to ask your permission. However, it’s pretty clear this app is a storage app, it’s not meant to provide analysis, explanations, and recommendations as such. Apple relies on 3rd party apps to do that for you.

The Health app on your iPhone is a real treasure trove of data. Not only does your iPhone and Apple Watch store data there, but so do most 3rd party health and fitness apps.

The Health app on your iPhone is a real treasure trove of data. Not only does your iPhone and Apple Watch store data there, but so do most 3rd party health and fitness apps.


Fitbit doesn’t have the luxury of embedding itself into the operating system, since it’s a 3rd party device and app. This means it has to sync it’s data to the Fitbit app on your device, which then sends the data to Fitbit servers to analyze. It works pretty well, just that sometimes you need to manually intervene to make sure it’s syncing all that data. Fitbit does a great job with the app though, with a nice customizable dashboard and lots of explanations for the data. No recommendations, though. There are extensive API and SDK available to create apps that connect with Fitbit. 

The Fitbit app stores all the data from your device, and provides useful tools to interact with it like simple challenges and notifications.

The Fitbit app stores all the data from your device, and provides useful tools to interact with it like simple challenges and notifications.


With a long and illustrious history in the early days of portable GPS devices and adventure gear, Garmin has started to directly target the likes of Fitbit with its recent consumer offerings in the Vivosmart family. The concept, price points, battery life, and overall experience are comparable to Fitbit. Garmin may have an edge in depth of features and content, but Fitbit definitely takes the cake on UX. The one bonus is that Garmin does sync most of its data to Apple’s Healthkit data store, making it easier to share and access from other apps.

Garmin certainly packs a lot of data and functionality incl. VO2Max and even SpO2 measurements. The app mimics Fitbit’s category-leading offering but falls short on UX.

Garmin certainly packs a lot of data and functionality incl. VO2Max and even SpO2 measurements. The app mimics Fitbit’s category-leading offering but falls short on UX.

Oura Ring

This is the minimalist’s choice for a wearable device. If the basic Fitbit models are read-only devices, then Oura takes that to another level — there is no screen or buttons or any UX at all. It’s just a ring with sensors on it. Lots of sensors. On top of the usual suspects, you get things like a skin thermometer. Apparently, the finger is a great place for a lot of those sensors due to the thin skin and stable position. Of course, they do have an app that reads, analyzes, and presents that data to you. Some of it can be synced to Apple’s Healthkit for sharing, and they have a new Cloud API available for direct integrations.

Screenshot 2019-05-10 at 2.10.25 PM.png

You sync data from the ring to the app and you get a whole lot of it to explore. Overall feel is quite scientific compared to the other apps.

So, now that we know where to find all this data, let’s examine what we can learn from it.

Physiological data

These are things happening inside your body. They can be indicators for your health and fitness, as well as daily changes in response to your activities. Usually, the cheaper end of trackers DO NOT include any of these capabilities, since it requires more expensive sensors. It’s well worth your while to consider this when looking for a new device!

Heart Rate

Most people are quite comfortable with heart rate data, and can at least roughly gauge what’s normal and what’s high.

Target ranges from low to high-intensity exercise, courtesy of

Target ranges from low to high-intensity exercise, courtesy of

What do I do with this information? Perhaps are more interesting usage of this is for analysis of your workouts. How intense your run was, and how much time you spent in your peak heart-rate range. Obviously, you wouldn’t want to redline your engine all day. Over time, you may start to see that you can run faster and longer while keeping the same heart-rate zone. That’s improvement!

NOTE: The latest Apple Watch also has a new sensor called an Electrocardiogram (“ECG”), currently only available for U.S. users. Basically, it’s a more accurate way of measuring heart rate, and can pick up irregularities. Apple, together with Stanford, has published research on what it can do here.

Resting Heart Rate (“RHR”)

This data is much more important than your real-time heart-rate. What’s the difference? RHR represents how much work your heart has to do when you’re relaxed. It’s not exactly the same as the lowest heart-rate you have when you sleep.

The reason RHR is important is that it’s a rough measure of your nervous system activity, hormone levels, and cardiovascular fitness. There is research to show that lower RHR means longer life.

So what’s normal for RHR? Well, the norms are actually a statistical definition, i.e. how much of the population falls under each range. It doesn’t really say what’s good. But for healthy athletic individuals, you would certainly want to see RHR below 70. Can it be too low? Yes, below 40 you may start to have problems.

Also worth noting, that this changes all the time. Slammed down those mojitos last night? High RHR. Stressing out at work? High RHR. Nearly died at the gym? High RHR. Lying in bed sick as a dog? Really high RHR. It represents the physical load on your cardiovascular system. If you make life harder for your heart, your RHR shows it real quick.

What do I do with this information? Making a habit of checking this every morning can tell you a lot about how your day is going to be like. Should you hit the gym, or hit the sack? Should you go out again, or go to bed early? A spike might also indicate you’re about to get sick, and trying to take it easy could prevent a full-on cold.

Fitbit ran their own study across millions of users to come up with averages per age and gender.

Fitbit ran their own study across millions of users to come up with averages per age and gender.

How does one lower RHR, then? High-level answer: exercise. Optimal answer: focus on stroke volume and cardiac output. Potential workouts:
1. Low-intensity Circuits

Heart Rate Variability (“HRV”)

Okay, so we know heart rate is your pulse. How many times the heart beats per minute. So what is this voodoo, then? Well, it turns out that the beats per minute aren’t steady. There’s a minute variation between each one. Some shorter, some longer.

This is some of the most interesting new data out there, because HRV is actually a representation of your central nervous system. If you’re not exactly sure what that is, it’s basically your wiring. How signals pass between your brain and the rest of your body. Analyzing this signal indicates if your body is in fight or flight mode, or rest and digest mode. Naturally, you wouldn’t want to unnecessarily be in fight mode which stresses out your body over time.

This is a very sensitive measure. It changes all the time, and it can change quickly. There are also many ways to measure it, but the current standard measure is rmssd, which is a statistical measure for that variability. Ideally, you would want to either measure this on a 24h average basis across many samples, or then just focus on a repeatable morning measurement before you get out of bed.

So what’s normal here? Even harder to gauge than RHR, because to be frank there isn’t as much research for HRV yet. Devices like Apple Watch that measure HRV have only been in the market a few years. What we do know about HRV (rmssd) is that if you’re close to 0, that isn’t good. It means your heart pumps like a metronome, which isn’t normal. If you’re close to 100, that’s good. Between the two, it’s harder to judge. A popular HRV measurement app, HRV4Training, has done their own research on this.

What do I do with this information? Well, since it’s far more sensitive than RHR, the same advice applies. It can be a very accurate measure of what state your body is in. The trend is more important than the absolute number. If much lower than usual, then take it easy. Maybe go for a walk rather than a hard run. If high, then go out and conquer the world.

Courtesy of, see URL above.

Courtesy of, see URL above.

How do you get more? So higher the better, pretty much. High-level answer: exercise. There is research (here and here) that shows some temporary changes through stretching, and some results through lifestyle interventions incl. diet and meditation, and some anecdotal evidence that shows different stressors like cold showers and sauna can boost your HRV. I’m sure we’ll see a lot more research on HRV in the future.


In terms of pure measures of cardiovascular health, VO2Max is as good as it gets. It tells you how quickly your body can process oxygen. The more oxygen per second, the more you can feed your muscles, the faster and harder you can go! If you haven’t seen this type of data from your device, it might mean you need to go for a few runs first for the device to get a reading.

So what’s normal here? There’s a range for normal people, that doesn’t include professional cyclists who can get into the 70’s. If you’re in the 40’s or 50’s, it means you probably get off the couch occasionally, at least.

Overview of VO2Max guidelines. There are more detailed charts per age, as VO2Max, like many other markers declines steadily with age.

Overview of VO2Max guidelines. There are more detailed charts per age, as VO2Max, like many other markers declines steadily with age.

What do I do with this information? Well alongside RHR, it tells you where you stack in terms of cardiovascular health. Again, you would want to have more, because besides your muscles your brain and well, all organs, also use the same system. More cardio, more life.

How do you get more? There’s a lot of good research to say that intervals are the leading cause of sky-high VO2Max. A routine you see cited often is running/cycling/swimming 4 minutes hard, then resting 4 minutes, and repeating 4 times. That’s 32 minutes of VO2 maxxing.

Behavioral data

These are things you do that affect your body. Things you do, that either promote or harm your health.

Sleep quality

Not all devices measure sleep out-of-the-box, incl. Apple Watch. In that case, you can look into 3rd party apps that provide that feature and data, especially if you want to measure sleep quality and not just hours.

We all know what it is, and we all remember our mother complaining about not going to bed early. Is there something new here? Well yes, there’s a rising amount of convincing research to show that your mother was right. Chronic lack of quality sleep is bad for you in many ways.

How do you measure sleep quality? Do you need to sleep like a log to qualify as good? There are in fact three phases of sleep, and you need all of them: Light, REM, and Deep. REM is famous, because of the 90’s band, and because it’s the dream phase. REM also drives memory retention. Deep sleep is the money sleep, that drives physical recovery and makes you wake up feeling energized.

So what’s normal here? Evolution designed animals to sleep 8hrs, or exactly 33% of each day. If you think of the evolutionary cost of sleep, in terms of lying unconscious among nocturnal predators, it must be pretty important. While sleep quality can be individualized, the obvious metric is if you wake up refreshed or not. Nobody can get away with 5hrs of sleep, and a few public proponents of low sleep, namely Ronald Reagan and Margaret Thatcher, both ended up with Alzheimer’s disease in late age. Don’t gamble on mental health.

What do I do with this information? There’s research (1, 2) to show how sleep affects everything from brain health, digestion, recovery, and productivity. It’s one of the easiest, cheapest, and fastest ways to improve your health. Note that the research interestingly also shows that sleep above 9hrs isn’t necessarily healthy. Best to stick to the sweet spot at between 7 and 8 hours.

How do you get more? So more might not just be more hours in bed, at least for most people the problem is quality over quantity. Most people need 7–8 hours of sleep, but to make the most out of it you want plenty of REM and Deep phase sleep, with minimal waking up in between. Common hacks include eliminating all light sources, turning off electronic devices, lowering the room temperature, and the right size pillow. Further, you would want to avoid TV, Netflix, Instagram, exercise, and even stretching before bed. You could instead try meditation or breathing to set your body in a relaxed, calm state.


Most devices make a difference between activity and workouts. Activity is like a brisk walk, where an elevated pulse and increased accelerometer means you’re moving. Does it replace exercise though? Sadly, not. Walking up a few flights of stairs and catching the bus with a 5-second sprint doesn’t get you off the hook for the gym.

In terms of things you can do to cheaply and quickly increase your chances of a long, healthy life, exercise is right up there. Really, there’s nothing like it. Research has shown that exercise can ever reverse many symptoms of aging, partially through changing the expression of hundreds of genes. It really is the magic pill you’re looking for! Several of the latest generation devices recognize workouts automatically, recording them on your behalf.

So what’s normal here? There are a few yardsticks for how much of what type of exercise is ideal, and certainly too much is possible. Following the research, there are specific longevity benefits to both cardio (1, 2) and resistance training (1, 2). So a bit of both would be ideal, dose depending on your starting condition.

What do I do with this information? The best thing you could do is to guide your weekly workouts with feedback from your biometric data. When your RHR or HRV is off, maybe just go for a walk. When it’s all good, go for the interval run or a bodyweight circuit. That way you know you’re doing enough, but not too much. This will of course change over time as your body is able to cope with more.

How do you get more? There’s a great risk here of overdoing the new year’s resolution, and getting cramped and injured leading you to completely fall off the wagon. Slow and steady wins the race. Go for consistency over quantity. Then over time as the habit sinks in, you can gradually explore more.

How can I use this data?

Okay, great. Now you know there are many interesting types of data at your disposal. So what?

The challenge is interpretation. Is it good, normal, or is it bad? What can you do to make it better? For some, like resting heart rate, you could benchmark for your gender and age group. Others change daily based on your actions.

This is what I realized when the Apple Watch came out. You need something on top to make sense of this data. So I created my own app, called Healthzilla.

Zilla has chewed your data into a digestible form, with easy colors to see what’s good (green) and bad (red).

Zilla has chewed your data into a digestible form, with easy colors to see what’s good (green) and bad (red).

It’ll give you an overview of what your health looks like using the above physiological and behavioral data from your wearables as inputs. Most people tend to focus on what their strengths are, but in terms of your health, it’s good to know where to improve.

If you already work out using your wearable device’s programs, or maybe other popular apps like Strava or Nike, then Healthzilla gives you a free stress and recovery analysis for those workouts. Based on your physiological data like HRV and RHR, as well as patterns of your workouts and sleep, we’ll tell you if today’s a good day for a Strava session or maybe settle for some mobility exercises and stretching. 

If you’d prefer to get personalized workout programs that also make use of your data, then we offer free programs incl. strength, cardio, and mobility that will put your workouts on autopilot, too. In fact, the whole app is free. So try it.

Try Healthzilla, now supports Apple Watch, Fitbit, Oura, and any Healthkit compatible devices incl. Garmin on iOS.