I get a lot of questions in my practice about wearables. Fitbits, Apple Watches, Whoop – they’re everywhere nowadays. All promise health benefits and most offer a premium subscription that claims it’ll help you live longer, healthier, and better. Any variable that can be tracked, from heart rate to skin temperature, will be tracked. If there’s money to be made from the device, that is…or more likely, from user data.
As a doctor, I’m often asked to interpret the data gathered by such devices. Sometimes, people will ask me if they think it’s worth buying a device, or what their targets and goals should be. Others, they’re looking for opinions as to whether or not the data gathered is reliable, or looking for reassurance based on an abnormal device reading. My goal with this article is to show what a physician thinks about when they look at wearables, and how that can help you decide which is “best” for you.
How do you decide which wearable is “best”? What’s hype, and what’s backed by real science? We’ll do a deep dive here and find out together. For the purposes of this article, I’ll be talking about consumer devices like fitness trackers. We’ll skip an in-depth discussion of other prescription devices, like blood pressure cuffs or continuous glucose monitors – though I am a huge fan.
Full disclosure – I wear and love my Garmin watch, and I have been an avid Fitbit customer for years. Neither of these companies nor anyone else paid me to write this article. Without further ado, here are my unfiltered thoughts on wearable technology:
What makes a "good" wearable?
When thinking about what makes a wearable good, it’s worth stating the obvious. We want the data output to be accurate, and we want to be able to do something about it:
Accurate:
- Wearables are only as good as the data they collect. We want to be sure that what we’re tracking is good data, especially if making treatment decisions based on it. If the data isn’t reproducible, the wearable isn’t worth wearing.
- We want to remember that data output is only as good as data input. More on that in a second.
Actionable:
- Assuming the data we’re looking at is meaningful, we want to be able to DO something about it. It does us no good to have information that can’t spur us to make a meaningful change. In fact, it might be demotivating to have that sort of data.
- Ideally, we want the device to make it EASIER for us to act on the data. We want prompts, suggestions, and immediate feedback on what to do next to improve.
How wearables measure: a deep dive
Most wearables currently on the market use three basic technologies to gather information:
- Photoplethysmography (PPG) – The fanciest word of the bunch, this is where most devices get their heart rate and pulse oximetry data. This is the purpose of the flashing green light on the back of your device. It’s a method to measure blood flow through your wrist. The amount of light reflected back to the sensor varies depending on whether the heart is pumping, or relaxing. This variation is used to estimate heart rate variability.
- Actigraphy – This is the sleep tracking component of most devices. It’s a measurement of motion and light. Because the body progresses through several different phases of sleep at night, measuring motion (or lack thereof) can give estimate how long someone is spending in a phase of sleep.
- Skin Temperature Measurement – somewhat self-explanatory, I am seeing this incorporated into devices in combination with other parameters. Body temperature varies based on lots of things, from phases in the menstrual cycle to getting sick with a cold. Most devices don’t give a specific number, but use it as a part of an algorithm to help predict things like ovulation or a high stress day.
Is this data any good?
It depends on who you ask, and how you measure.
I mentioned earlier that data output is only as good as the input. Here’s where the real nuance of wearable technologies comes in.
PPG is a very widely used technology in hospitals across the country. If you’ve spent any time in a hospital in the past, you probably know it better as a pulse oximeter. The major problem with PPG is that it is easily fooled. Ambient light, skin tone, sweat, hair, hydration status, and changes in peripheral blood flow can all lead to inaccurate readings. This might not be a huge issue for something like heart rate, which can be easily validated by checking your pulse, but it’s a much bigger issue for a readout like oxygen saturation, which can be life-threatening and isn’t easily verified. Pulse oximetry’s troubled history of racial bias is certainly worth reading about as well.
Actigraphy isn’t without its pitfalls, either. As anyone who has sat on the couch for too long knows, devices can misinterpret lack of movement as sleep, and thus tend to overestimate sleep duration as a result. It also isn’t that useful in detecting certain common sleep disorders, like sleep apnea.
Skin temperature sensors struggle from some of the same issues as PPG, with the additional complication that the data in isolation just isn’t particularly useful, and we might not even know what a real “fever” is.
What features are worth having, then?
With all that out of the way, I DO think there’s a place for wearables for improving your overall health and wellness. There are really only two features that are worth looking for, in my opinion:
- Real-time heart rate zone feedback – I am a big fan of “zone” training when it comes to fitness. The American Heart Association recommends 150 minutes of “moderate” intensity cardio (or 75 minutes of “vigorous” cardio) weekly for cardiovascular health. Going by “feel” when it comes to activities like this, though, can be misleading, especially when you’re just starting exercise, or when you’re already fairly athletic. Heart rate zones are a nifty way around this problem. As a more objective measure, they can help illustrate how your level of effort translates to your target heart rate. This immediate feedback can help you avoid over or under-training, telling you when to push further and when to pull back with your workout efforts. This is where PPG shines – heart rate trackers are a FANTASTIC way to ensure you’re getting a good workout, with the caveat that if you’re taking medication that impacts the heart or you have a condition that doesn’t allow your heart rate to elevate or respond to changes normally, you don’t get much benefit from zone training. For general health and wellness, though, real-time heart rate zone feedback is invaluable.
- Basic sleep tracking – Even the fanciest trackers use some form of actigraphy to measure movements during sleep. While this isn’t usually enough to confirm a serious sleep disorder like sleep apnea, it DOES give you a ballpark estimate of how many hours if sleep you’re getting a night. Many trackers will also remind you when it’s time to wind down, or wake you up with a gentle vibrating alarm – all of which are helpful for promoting good sleep hygiene and getting you thinking about healthy sleep habits. I think that’s a great place to start with most people, and a tracker can help keep you accountable and remind you when it’s time to wind down.
What about EKG, stress monitoring, and everything else?
A quick word about several other popular features:
- EKG Function – Although it’s becoming more popular in many fitness trackers, it might not be as useful as you think. A smartwatch EKG can’t tell if you’re having a heart attack – you need a more comprehensive evaluation for that. It might be able to screen for certain types of arrhythmias like atrial fibrillation, but the evidence is inconclusive that this is helpful for most people. If your watch does register something abnormal, it’ll most likely need to be confirmed by a medical-grade device before treatment can be initiated. As algorithms and detection devices improve, I actually think this function might become more useful over time. But as for now, it probably isn’t worth the extra spend, unless there are other features bundled in.
- Stress Monitoring – most fitness trackers today include some form of “stress monitoring”. This is usually derived from a proprietary algorithm that draws heavily from heart rate variability. The problem with this approach is that stress is a complex physiologic phenomenon that is the result of an interplay between physical and psychological state. Ironically, alerts about stress from a wearable may actually increase stress in individuals, not decrease it. You’re better off learning how to self-monitor your stress in concert with an excellent therapist.
- Pulse oximetry – because of the problems with PPG and the potentially devastating consequences of a low oxygen level, I don’t recommend putting much, if any, stock in the reading your wearable spits out. If you’re concerned about your blood oxygen level, you need to be seeing a doctor, not checking your watch. I’d skip this feature altogether in a wearable if I could – it’s not likely to help you, and it may hurt you.
- Menstrual cycle tracking – There are now a few devices/products/apps on the market that advertise wearables for women’s health issues. I’m not an OB/GYN, and this is by no means my area of expertise. For the reasons we discussed above about the pitfalls of skin temperature monitoring, I’m not sure I’d use a wearable in isolation to draw any major conclusions about menstrual health.
Give me some names, doc!
So which wearables are the best? I’ll break it down by group:
- For general health and wellness, any basic fitness tracker that measures heart rate, active minutes, and optionally sleep will get the job done. It’ll get you moving, and give you some basic feedback on healthy sleep habits. I think this is a fantastic place for most people to start. Most people are familiar with Fitbit’s line of fitness trackers, but there are a whole host of other competitors now making similar products – Garmin, Polar, Whoop, Huawai, and Amazfit are all big names in this space.
- For sport-specific athletes, if you’re going to spend more, consider a tracker with additional features that compliment your sport rather than features like EKG, stress reduction, or pulse ox, which don’t help much. Runners might enjoy a GPS-enabled watch, while swimmers might prioritize waterproof devices that can track laps. HIIT athletes might like a nice display that tracks their HR zones, while golfers might need a peripheral that measures club head speed or distance to the pin. Don’t be fooled by “proprietary” algorithms or gimmicks like an EKG or stress tracking – most of these trackers are working with the same raw data, and while these tools are flashy, they aren’t likely to give you much more information than a basic fitness tracker would. Garmin makes a lot of sport-specific products like this, but Apple (ignore the hype about pulse ox being banned – you don’t need it anyways), Samsung, and Google all have GPS-enabled products that might be value added.
- For patients with cardiovascular or pulmonary disease or arrhythmias, I would stick to validated, FDA-approved devices prescribed by your doctor. It isn’t wise to trust your afib or history of a heart attack to a smartwatch, and the 2-lead EKG offered with some devices is probably going to be more misleading to you than helpful. Similarly, pulse oximetry isn’t that helpful in isolation, and probably needs additional medical help to interpret. If there is something abnormal that your watch or other device detects, you’ll want to let your doctor know right away. Sticking to approved devices like remote patient monitoring equipment monitored by a clinical specialist is probably the safer option for most people.in these categories, as readings can otherwise be misleading.
Conclusion
The best wearable for health and wellness is the one you’ll wear and use to improve fitness. There’s a lot more alike about these trackers than different. In summary, prioritize heart rate training, then sleep if you’re looking for features, but recognize all wearables have limitations. Always check with your doctor before starting any exercise regimen.