How to Read Your Wearable Data (HR, HRV, Sleep Explained)

What is your wearable device actually telling you?

In this episode of Health Recoded, we break down how wearable devices like Whoop, Garmin, Oura Ring, and Fitbit track your health data and what that information actually means.

If you use a smartwatch or wearable device and want to better understand your heart rate, HRV, sleep score, and other health metrics, this episode will help you learn how to interpret your data with more clarity and less anxiety.

Many people don’t realize that wearable devices are not providing exact medical data. Instead, they track trends over time. Without that context, it’s easy to rely too heavily on the numbers or assume something is wrong.

In this episode, we explain how wearable technology works, what each vital sign means, and how to apply that information to your daily life.

We cover:

- The vital signs your wearable device tracks (heart rate, HRV, sleep, SpO2)
- What each metric actually means in the body
- The difference between wearable data and clinical vital signs
- How to interpret your wearable health data accurately
- When to pay attention to your numbers and when not to worry

If you’re looking to better understand your wearable data, improve how you use your device, or reduce anxiety around your health metrics, this episode will give you a clear starting point.

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Chapters:

00:00 Intro
00:53 What your wearable device is tracking
01:18 How wearable technology works
01:55 Are wearable devices accurate?
06:09 How to interpret wearable health data
07:29 When is low heart rate concerning?
15:44 What is HRV?
19:15 Is high blood pressure bad?
23:55 How to interpret SpO2
26:15 How to interpret your sleep score
29:29 Key takeaways

This content is for educational and informational purposes only and is not a substitute for medical advice from your healthcare provider.

Resources:

American Heart Association. (2024). Target heart rates chart

https://www.heart.org/en/healthy-living/fitness/fitness-basics/target-heart-rates

American Heart Association. (2023). Understanding blood pressure readings

https://www.heart.org/en/health-topics/high-blood-pressure/understanding-blood-pressure-readings

Pew Research Center. (2020). About one-in-five Americans use a smartwatch or fitness tracker

https://www.pewresearch.org/short-reads/2020/01/09/about-one-in-five-americans-use-a-smart-watch-or-fitness-tracker/

Cleveland Clinic. (2022). Heart rate variability (HRV): What it is and why it matters

https://my.clevelandclinic.org/health/symptoms/21773-heart-rate-variability-hrv

Cleveland Clinic. (2023). Blood oxygen level: What it is and how to increase it

https://my.clevelandclinic.org/health/diagnostics/22447-blood-oxygen-level

Bent, B., et al. (2020). Investigating sources of inaccuracy in wearable optical heart rate sensors

https://www.nature.com/articles/s41746-020-0226-6

Shcherbina, A., et al. (2017). Accuracy in wrist-worn sensor-based measurements of heart rate

https://jamanetwork.com/journals/jamacardiology/fullarticle/2588768

Harvard Health Publishing. (2021). Tracking your sleep: What works and what doesn’t

https://www.health.harvard.edu/staying-healthy/tracking-your-sleep-what-works-and-what-doesnt

de Zambotti, M., et al. (2019). Wearable sleep technology in clinical and research settings

https://academic.oup.com/sleep/article/42/5/zsz048/5420819

Topics covered:
wearable devices, smartwatch health data, how to read wearable data, heart rate, HRV, sleep score, SpO2, wearable accuracy, how wearable technology works, Garmin, Whoop, Oura Ring, Fitbit, health tracking, vital signs, how to interpret health data

Transcript

SPEAKER_00 0:00

Hundreds of millions of people are wearing devices that track their health every single day, and most have no idea what that data actually means. Hi, I'm Alex. I'm your nurse, and I have spent years in healthcare monitoring other people's health and their vital signs. It can be overstimulating to receive so much information and not know what to do with it. Whoop, Garmin, Aura Ring, these are just a few of the wearable devices that are gracing people's limbs these days, and they provide a lot of solid data and health information. But what are we actually doing with the information that we receive from them? Your wearable tracks your heart, your sleep, your stress, but without context, it's just numbers on a screen. So I'm gonna help with that today. We're gonna explain each vital sign, what it means, but most importantly, how can we interpret that data to actually affect our everyday life? So, what your wearable is reading, typically most of them on average will read your heart rate, your HRV, your sleep data, and then some of them will track your cycle for women, and this is through temperature. Others might track your blood pressure and your oxygenation, which your SPO2. We'll talk a little bit about that. Not all of them do it, and they're not super accurate, but we'll save that for a second. How are they reading it though? The science behind the tech is what's called PPG, so it's photoplethismography, and essentially it's just light sensors on the device that detect blood flow changes. So these accelerometers also track movement, sleep, activity, and then there's also temperature sensors and they track skin changes, so the temperature in the skin. And so, big idea here, they shine light into your skin and they measure how blood flows with each heartbeat and the information and the data that that carries. So, what is the difference between your vital signs that you would maybe get taken at the doctor's office or in hospital, and then the wearable information that you're getting? There are accuracy questions here. I have worked with so many different machines and devices, and as a basic rule, clinical medical devices are going to be much more accurate than the device that you're wearing on your wrist or on your finger. That being said, they can still be pretty good at tracking data, but they're best for tracking trends. They're less reliable for exact numbers. So ultimately, they're not gonna be diagnostic tools. We're gonna want to watch the data that your whoop or your garment or whatever you're wearing is presenting to you over time. Okay, so we're gonna want to watch the trend. And we're still watching trends when we're at the hospital monitoring your data, but we can do more with the more specific data that we're getting from something like the blood pressure machine or the pulse oximeter, or specifically the more invasive lines, like an arterial line that we would put in your wrist to monitor your blood pressure, things like that are going to be much more accurate. So, some common myths around the different information that you're getting from your device. Your HRV drop, so something is automatically wrong. You got a bad sleep score, so you're unhealthy, or you had one abnormal reading on anything, and it means that there's automatically a problem. We don't want to freak out about the data. Your wearable doesn't tell you what's wrong, it tells you what's changing. So, again, we want to make sure that we're paying attention, but also it's over the long term and we're tracking the trends. What I was talking about earlier with the blood pressure and the oxygenation, these are not always included in every device. Most wearables do not directly measure your blood pressure, at least reliably, and then only some of them will monitor the oxygenation, but it's also the ones that do, it's kind of limited, and this is based on the wearability of it. It's less accurate, again, than medical pulse oximeters, but it's especially unreliable given constant movement if you get cold extremities, and then also those with darker skin tones. So the sensors on the device just don't read nearly as well, and therefore that can lead to less accurate information. And ultimately, these things are also issues that we see at the bedside. We have to change the pulse oximeters more frequently because of the movement in the cold extremities in XYZ, so you want to keep that fresh and clean, but still those are gonna be much more accurate than what we're getting here. That's not to say that these things aren't useful, okay? So I don't want you to sit here and listen to me say all this and think that I'm saying that you shouldn't wear a device or a trackable and that you always have to get your vital signs at the hospital. That's not my point. We're just dissecting the differences here. So then with the temperature and the cycle tracking, I think Whoop and Aura are two of the only ones that do it. I personally have Ring Con and they track it as well, but it's typically more with a cycle pattern tracking. So they do detect with your skin temperature and it's not your core temperature. So this is why there's still some question as to the accuracy and the efficacy of it, but they are getting better, and I think they're getting more and more accurate, but the limitations are influenced by environment, sleep conditions, alcohol, because ultimately, again, this is just showing the trend over time as opposed to what's actually going on inside your body. Okay. Ultimately, big idea here. Wearables estimate, they don't diagnose, they show trends, not single point accuracy. And clinical vitals are in a controlled environment with calibrated tools, so they're gonna be much more accurate. And wearables are real world and continuous, so therefore they're less precise, but we can still track relevant data and trends over time. So they can be very useful, particularly those of us that are really health conscious. So, all of that being said, what can we do with this information and how do we interpret it? So, first, I always want to preface with this: don't freak about the data. Just because you get one wrong reading, or not even wrong, but one off reading, maybe it's not your normal or your baseline. It doesn't mean that something is wrong with you or that you are broken. It's just information providing feedback on how your body is doing. And you're not broken if anything is out of range. We'll go through each of these vital signs though, and we'll explain what they mean, and then also what is out of normal and what we can do to adjust safely. And I want to go ahead and preface, I say normal with quotations because ultimately normal, we have ranges, particularly at the bedside, in the hospital, in medical, I should say. In healthcare, we have normal ranges for where ideally the body should be operating with these different vital signs. But again, it is a reference. If your heart rate is normally lower and then it's a few clicks higher, and that's not normal for you, but it's still within range, you're still technically within range, you're still within normal, but it's not normal for you. So, yes, these ranges are quote unquote normal, but we want to make sure that you are at your baseline above anything else. Okay. So we're gonna start with heart rate, and this is the rate at which your heart beats and pumps blood throughout the body. So it reflects cardiovascular demand and nervous system state. So the healthy range is roughly six to one hundred beats per minute. The disclaimer here, and I'll make this again in a minute, athletic people can easily sit below that. So if 60 to 100 is normal, 40 to 60 for an athletic person, particularly at rest, particularly with sleeping, is no concern. There's people that I've had before that have come in and they've been asleep and they were 30 or 35, and that would normally be very concerning. We would want to be doing things to adjust that heart rate, but for that person, they were resting, they were fine, they were asymptomatic, meaning they didn't have symptoms, and as a result, they were fine, they were healthy. So when is your heart rate a concern when it's symptomatic? Okay. So below 60 is bradycardic, which means slow heart rate, and above means tachycardic, which means high heart rate. So if you're experiencing a lower heart rate than normal, let's say you sit at 60 and it goes to 50, and you're suddenly starting to not feel so great, and you can't really catch your breath, and you're feeling really fatigued or you're feeling really dizzy. That is symptomatic, okay? If you drop to 50 and you're chilling and you don't feel any different and everything's okay, then you're asymptomatic, and there's not really anything that you need to do besides just kind of chill and monitor it. So, what raises our heart rate and what lowers it? Exercise raises it. Stress and anxiety because of the nervous system activation. Illness and fever can cause your heart to um it can cause your heart rate to go up, and I'll talk about why in a second. Um, caffeine naturally, and then also dehydration. And caffeine is actually dehydrating, which is part of why it makes your heart rate go up, besides how it acts on your heart. So, what raises heart rate? Exercise naturally, because we're getting up, we're moving, we're making the heart work and pump more, so that'll make the heart rate go up. Stress and anxiety, same kind of thing. The body is in a sympathetic response, it's in fight or flight, it's perceiving a stress. So it's trying to activate you, it's trying to make the heart pump faster so that you have more blood to your peripherals, your muscles, so that they can function and work and get you away from the bear or the stimulus or whatever it is. And then illness and fever can increase your heart rate because the heart is having to work more and pump harder in order to do what it needs to do in order to heal you, but it could also be because of dehydration. So if you're sick and you're not taking in enough fluid, then your blood volume goes down. So because you don't have as much fluid in the blood, that means that the heart has to work more to pump less. So then that heart rate goes up. Okay. So then on the inverse, what lowers the heart rate? So fitness, sleep, and relaxation. So sleep and relaxation are kind of the same. We're in a relaxed stress, or sorry, relaxed state. So we're in a parasympathetic response. So the body's in rest or digest, and it doesn't feel the need to increase the heart rate to make you move. So we're just kind of keeping status quo. For fitness, it's not so much as like exercise when you're in the moment that's gonna increase your heart rate, but fitness overall. So again, athletic people like I was talking about, you will have a higher stroke volume, which means your heart is pumping more effectively. You have higher contractility in the heart muscle. So essentially, the heart muscle is stronger and it can more effectively do what it needs to do. And as a result, it's not going to have to work as hard to do it. So your heart rate will naturally sit a little bit lower. Okay. So that's more of a long-term what lowers the heart rate, as opposed to like sleeper relaxation causing a lower heart rate. So, from a nursing perspective, context matters more than the number. This is what I was talking about with being symptomatic. If it's too low and you're having symptoms, then I'm concerned and I'm trying to do something about it. Because if your blood pressure, or sorry, if your heart rate is too low, that means you're not getting enough blood pumped through your system and blood carries oxygen. And if you don't have enough oxygen getting to all the different muscul musculature and organ systems in your body, then you're not getting enough perfusion. And so every organ system needs oxygen, and so the oxygen is what keeps your organ systems alive. So essentially, if you're not getting adequate enough perfusion to these different organ systems, particularly your brain, that's when we start to see other problems and symptoms, particularly necrosis. And necrosis means death. And this is like way on down the line, okay? So you're getting a picture into my nursing brain of how I'm thinking 20 steps ahead. But that's how we're trained to think because you have to know each one of these steps and what the next piece means, so that we can ideally stop that at step two so that we don't get to step 20 and we can avoid that really big bad response. Okay. So again, just because your heart rate goes low doesn't mean you're gonna die. I'm not trying to scare you. I'm just trying to give you some context into what I'm thinking about and what I'm looking at when I'm seeing your vital signs if I'm your nurse at the hospital. So then the high heart rate, again, heart is working over time to pump blood. So my concern here as a nurse is high heart rate could mean that your heart gets tired eventually and bottoms out. Think about when you're going on a run or you're doing an exercise. You only have so much capacity. You can't do that forever. Your heart can't and shouldn't sit at 150 beats per minute all the time. So at the bedside, when somebody would spike their heart rate, that's concerning. But if it stays that high for too long, that's even more concerning because I know, again, 20 steps down the line, they may bottom out, they may drop to 30, and that means the heart's giving up, and that's a problem. So again, I'm just giving you worst-case scenarios so you can see more of the context of what I'm thinking about as a nurse when we're talking about these things. But ultimately, your higher heart rate that you're reading from your wearable could just be stress-related or from the exercise or just a situational experience. But if you're noticing that your heart is ticking along and you're feeling all these other symptoms that we talked about, then that would be something to pay attention to and maybe go get evaluated. So, the short term, what can we do for a low heart rate? Again, if you're feeling symptoms such as dizziness or you're fainting, we want you to seek care because there's a further evaluation that's needed in order to determine what's really going on. For the heart rate, we want to first check maybe you're dehydrated, and again, like we talked about, you just need more blood volume for your heart to be able to pump. Or maybe you're stressed and you're feeling activated there. So we could do some deep breathing to help bring down that vagal tone, like we were talking about. Remember when we did the breath work uh in the nervous system episode, I believe? We're basically doing what we call a vagal, and so we're forcing that to be activated to calm ourselves and bring us down. So reduce stress, reduce activity, drink, hydrate, get something, and see if it comes down progressively over time. But ultimately, if you're feeling more and more symptomatic and these other things are not helping, then go get evaluated as well. Moving on to heart rate variability. This typically measures or this is typically used in determining rather stress levels. So your heart doesn't beat just like a metronome where it's the same every minute. It alternates, even if it's just one or two clicks. Maybe you're 63, and then you're 65, and then you're 64. That's okay. We want that adjustment. We want the heart to be able to adjust. So HRV, heart rate variability, measures the variation in time between heartbeats. So the variability between the rates is used to determine recovery and resiliency. So essentially, what we're measuring is okay, you were in a lower heart rate here, and you're in a higher heart rate here. Maybe you were stressed here, maybe you were relaxed here. How quickly did you bridge that gap and get from the lower to the higher, or the higher to the lower? And it's the time between the variability, I believe, is what the HRV is measuring. This one's still a little bit form uh sorry, foreign to me. I'm not measuring heart rate variability at the bedside. I'm looking at all other different kinds of like hard data points, and this is just not something that we evaluate. But it's still important because your wearable is reading it, so we're gonna talk about it. So ultimately, HRV, a higher HRV typically indicates a stronger recovery. I think it can range anywhere from like two to 200, but I think roughly around 100 is what I've heard, is a pretty solid number for your HRV. But we're not necessarily looking for good or bad. Absolute numbers matter less than your baseline. So a 20 for you may be great, and a 20 for someone else could be really not. But higher HRV typically means better autonomic flexibility. It doesn't just mean you're good. And a lower means maybe you're going through poor recovery or stress or illness. It could mean you're just going through something. But it's ultimately relative to the individual and it's subjective to the context as well. So I don't want you to think, oh, I have a super low HRV and this other person has a really high HRV. They're better than me. It is so easy to get into that mindset. HRV is not a number that you're comparing with somebody else, you're comparing it with yourself. So factors that lower and factors that raise. So factors that lower your HRV could be alcohol, poor sleep, illness, psychological stress, maybe you're overtraining, not getting enough sleep, not recovering appropriately. So that's what that is showing you is that your body is staying in that stress response and not recovering nearly as effectively. So factors that increase the HRV could be good sleep, recovery, meditation, breath work, aerobic fitness. You're doing and supporting, you're doing what you need to support your body in order to recover and therefore fostering that resiliency. So HRV doesn't mean that you're bad. It just is a number in order to help determine what your recovery and your stress is looking like on a day-to-day basis. So I am gonna talk about blood pressure and SPO2, which is oxygenation. Um, again, remember this is gonna be a little bit more in the context of the bedside because or rather healthcare because some of these devices don't track these, but this is still helpful information to know. So blood pressure is the measurement between contraction and relaxation of the heart. So it measures how effectively your heart is pumping. So this comes back a little bit more effectively to the contractility and the strength of your heart that I was talking about. So heart rate is the speed at which it's pumping, but blood pressure is more about the effectiveness to which it's pumping, is kind of the best idea to give you here. So the normal is 120 over 80. Okay. I'm not gonna sit here and dissect the diastolic and the systolic and all that stuff. We're not gonna get into it. I just want you to understand the basics of what this is telling you. So again, athletic people can sit lower. We talked about how fitness can lower your heart rate over time. Better contractility and improved blood flow can result from exercise and being at a healthier and fitness level. Um, but the heart is typically stronger and more effective because you've exercised it so continuously, and therefore it doesn't have to work as hard to do its job. So your number may sit lower. I think mine is like 100 over 60 on average. A low blood pressure at the bedside, I'd be concerned if I saw somebody in the 90s to 40s. That would be something we'd be like, okay, that's kind of low. We need to do something. But then on the flip side, a high blood pressure, I'm I mean, technically, hypertension. I think when I went through school, it was ranked as 130 over 90 or yeah, 130 over 90, I think, technically. But particularly in our day and age today, with how our society functions, it's much more common for people to have higher blood pressure. And hypertension is a very common comorbidity. So both can be dangerous, but both can also be normal. And this again is dependent on context. So low blood pressure concerns, symptoms matter. So again, if you're symptomatic, this is when we want to do something about it. I sit at 1 over 60, normal. If I was at 130 over something or 140 over something continuously, and I was just chilling, or I felt well, not just chilling, but like I was there and there wasn't a stimulus, right? So I wasn't in a context like exercising where it would be higher and that would make sense, but I was feeling these symptoms. Of fainting or weakness or dizziness, I would be concerned and I would need to go get evaluated. So if you're feeling symptoms, then we want you to go get checked, okay? So I am talking about low blood pressure, and I realize I said high, but low blood pressure concerns, symptoms matter. Dizziness, fainting, weakness. If your blood pressure is lower than your normal and you're experiencing these side effects, please go get evaluated. This means that your blood is not pumping enough to your brain or to the other body systems. And this comes back to lack of oxygenation. We really want to make sure that the heart is pumping effectively and getting blood to where it needs to go so that it can get oxygen and everything can function. Okay? So high blood pressure concerns, this can often be silent. Lots of people have come into the hospital and say that they had normal blood pressure, and then they're sitting very, very high, and they're concerned, or surprised rather, as to why we're so concerned as what's going on. They didn't know their blood pressure was as high as it was. The long-term risks here are stroke, heart disease, kidney disease. The concern here is pressure, right? So if the heart is pumping at that high of pressure, it creates more pressure in your vasculature. And so as a result, all these systems are connected. So you're at a higher risk for stroke or at higher risk for kidney disease because it's got so much more pressure that's being applied to it from your heart working so much more long term. So again, if you're symptomatic and you're outside of your baseline for where you normally sit for your vital signs, that is when you would want to go seek care and attention. Okay. For oxygenation, this shows how much oxygen is in the blood. And it's important to know for perfusion, like I was talking about, so oxygenation into your organs and your muscle tissue, essentially. So the lack of oxygen for a prolonged amount of time, and this is like a very severe lack of oxygen, could mean tissue necrosis or death. So this is why it's so concerning if somebody passes out or isn't breathing, because the more time that you go without oxygenation to your brain is unfortunately something that you can't get back. And that is more time that the brain is not getting blood and oxygenation and is there for dying. So again, worst case scenario here. But normals for oxygenation would be really for the average person, it should be 95% or above. When we're in the hospital, it's roughly 92 to 93 percent or above. But within that relative range, anything below that, we're getting kind of concerned. And this is for a healthy individual without any lung issue, condition, or problems, right? So we want you to be sitting mid-90s or above, and that's a healthy level. So if it is low, take deep breaths and hold for a few seconds to allow the oxygen to perfuse in your lungs and ideally get into the bloodstream. So I don't want to cause you to pass out because you're holding your breath for so long, but literally just take a deep breath, hold it for a few seconds, push it out, take a deep breath, and then do it again, like one to two seconds, okay? Avoid fast breathing as well, because that could also cause you to pass out because you're basically increasing the CO2. So rapid breathing can cause lightheadedness due to the carbon dioxide changes that are happening in your lungs, blood, brain. And so we want to try to avoid fast-paced breathing, okay? That's gonna hinder as opposed to help. All right. She cannot be forgotten. I know this is one of the big reasons. I think, second to HRV, that a lot of people get wearables, is so they can track their sleep. Ultimately, sleep staging in a wearable is estimated. It is not exact. An EEG in sleep labs is the gold standard for getting any kind of true insight and diagnosis into your sleep and what's going on. So these wearables, again, do have limitations, and again, they are just insight into what is going on as you're sleeping, but it's better than nothing. So the sleep stages and roughly the percentages that we want for each of them. Light sleep is roughly 45 to 55 percent, deep sleep roughly 15 to 25 percent, and then REM cycles 20 to 25 percent. So the most would actually be the light sleep, and then deep sleep and REM alternating in there as well. But then it should also be tracking your micro awakenings. So if you're waking up in the middle of the night and you don't even know it, maybe you're turning over or you're coming out of that sleep cycle, even if you're not aware of it. Or maybe you did get up and you were awake consciously for a while, or you went to the bathroom or something, but those micro awakenings can actually be a pretty big indicator into what's going on to your health and to your recovery. So deep sleep equals physical recovery. That's when you're getting the most rest and restoration ultimately for your body. And then REM cycles are typically where cognitive and emotional processing are occurring the most. So, what matters more than the stages is your total sleep time, your sleep consistency, and then your wake interruptions. If you're getting lots of wake interruptions, then you maybe have something going on and your body's not recovering and resting as much as it should. And then, as well, if you're not getting enough sleep, you're not getting enough time to cycle through these different sleep phases for your body to recover. And so ultimately, we don't want to obsess over the stages. Again, we want to focus on patterns, but this is still relevant information with us with which we can do something with or at least know about so that we can fix whatever needs to be fixed. And I know it can be really stressful to see that you got a really bad sleep score. I would encourage you to look at the hard data, look at what the device is actually telling you, and then see the interpretation from there. I have personally had my ring con tell me that I got really poor sleep, and I slept for 12 hours and I felt great. And it told me sleeping too long can cause heart conditions or something like that. It's like, okay, it was one night. Like I obviously was tired and needed a long amount of sleep. So take it with a grain of salt. It's information, again, tracking trends over the long term that we want to see and want to pay attention to. But just because you got one rough night or one weird score doesn't mean you're broken, doesn't mean that anything's wrong, and you're gonna be okay. Don't obsess over stages, focus on patterns. So, my key takeaways for you your wearable device and the data it provides are just a window into what your body is actually doing. And it's providing that in order for us to be able to view what's going on inside. You're not broken if any of your data is slightly different than somebody else's, or if your data gets off a bit from day to day, that is expected and normal. The information wearables provide can help us pay attention to the messages that our body is trying to send us. So interpreting that information is important to safely and appropriately look after our bodies and our health as a result. Ultimately, it's not about control, it's about insight. If you know someone who has a wearable device, maybe share this video with them. They may benefit from learning more about what their device is actually telling them. I'm always available. If you ever have questions, you can reach me here in the comments or follow me on Instagram. I'm at health recoded podcast. If today's topic helped you, please consider subscribing. I love talking about all different kinds of health topics. So I'm interested to hear about any other topics that you want to learn about or talk about. I'm here every week to help you understand your health and your body better. I'll see you guys next time and thank you for listening.