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What to Look Out for in the World of Wearable Health Tech

Key Takeaways:

  • Wearable health tech includes a huge range of wristbands, watches, and rings, as well as CGM (continuous glucose monitoring).
  • Sleep stages are not always accurately measured by wearables and should be interpreted cautiously.
  • The more inputs there are (including heart rate, temperature, and oxygen saturation), the more accurate the sleep data is likely to be.
  • Watches with ECG measuring ability can alert you to irregular heartbeats.
  • No wearable tech gives a reliable figure for calories burned.
  • CGM is only properly proven for people with diabetes but can also give anyone detailed data on how food and activity affect your glucose levels, helping to build healthy habits.
  • Wearable health tech can help with health optimization, but shouldn’t be used to diagnose illness or in place of medical care.
  • It can be a slippery slope between using health data for optimization and becoming obsessive and anxious about it, so always remember to stay focused on the bigger picture.

From the early days of analog pedometers attached to your waistband, wearable health tech has come a long way.

Now there’s an ever more sophisticated range of health monitoring wristbands, watches, and even continuous glucose monitors. Teamed with smartphone apps to interpret all that data, the personal health data we can have at our fingertips is pretty awesome!

I personally like the Oura ring, which I’ve used to help improve my sleep patterns. But each wearable has a specific focus that will appeal to different people depending on which areas of health or fitness interest you most.



The internet is already overflowing with reviews of all the popular wearables (Oura, WHOOP, Fitbit, Garmin watches, etc), so for this article, I think a more useful approach is to run through the key health and fitness parameters these digital health devices measure.

That way, you can decide what you most want in a wearable device — and then find the device that provides this functionality. You may decide you don’t want to go down the wearable tech route at all.

Let’s get to grips with the potentially useful metrics wearables have to offer.

Wrist-Based Wearable Health Tech – Sleep and Movement Basics

Most wrist-based trackers will assess your physical activity by including a 3-axis accelerometer that continuously senses the movements of your body (i.e. whether you are walking forward, running fast, or even just standing/lying still). Pretty much every wrist-worn tracker will also measure your real-time heart rate at rest and during exercise, while most include a step counter.

Almost all wristbands will also give you sleep data if you wear it at night — usually how long you were asleep in total, how long it took you to nod off, how long you were in REM, deep, and light sleep, and the number of disturbances you experienced.

These basics can be informative when tracked together. For example, you can monitor how your resting heart rate changes over time, challenge yourself to work up a sweat, or make changes to your routine to see how it improves your sleep.

Sleep Tracking Limitations

The latest, sleep tracking devices with heart rate monitors are more accurate than the first-generation models that just employed motion sensing. But even with these refinements, research suggests that trackers aren’t always accurate, in some cases underestimating deep sleep by as much as 46 minutes a night [1]

If accurate sleep tracking really matters to you, choose a sleep tracker that collects data from as many as inputs as possible (as well as heart rate and movement, these can include skin temperature sensors, and the HRV and SpO2 measures we discuss below).

However, bear in mind sleep trackers are not medical devices, and no wrist-worn tech is ever as accurate as gold-standard polysomnography (sleep tracking in a lab) which involves having electrodes attached to the skin and scalp. 

Also consider whether you would do better being tech-free when it comes to sleep. I’ve occasionally needed to advise patients with insomnia to take off their smartwatches and fitness trackers at night to avoid sleep becoming a preoccupation that leads to further sleeplessness. 

We’ll touch on the potential downsides of continuously monitoring your health with wearable tech a little later in this article. Remember also that sleep tracking devices can’t diagnose a sleep condition, such as sleep apnea, or a circadian disorder. 

Before going into more detail on the other sophisticated health metrics that wristbands and watches can measure, here’s a summary of the most popular products and their key features. We’ve added a column on GPS capability because if you are seriously into fitness, a watch with inbuilt GPS to track runs, bike rides, and swims is essential. Garmin, Apple Watch, and Fitbit devices all offer these enhanced performance metrics.

Comparison of The Most Popular Wrist-based Health and Fitness Tech

SleepTrackingHRVSpO2StepCounterOn-Board GPSECGMonitoring
WHOOPXXX
Garmin✔ (some models)✔ (some models)✔ ✔ (some models)
Apple Watch✔ (via Breathe app)✔ (some models)
Fitbit✔ (some models)✔ (some models)
Oura RingXX

Heart Rate Variability (HRV)

Heart rate variability is literally how much variance there is between each individual beat your heart makes. For example, if your heart beats at 60 beats per minute, each beat is unlikely to be exactly 1 second apart. Instead, one completed beat might be 0.95 seconds, and another might be 1.05 seconds, for example.

The reason that HRV has become an important health and performance marker is that higher HRV tends to indicate increased cardiovascular fitness and can also mean your body is under less stress and more ready to perform. Higher HRVs have also been linked with longer lifespan [2], while there also seems to be a link between low HRVs and mental health conditions like depression and anxiety [3]

Variation between heartbeats is controlled by two opposite branches of the autonomic nervous system, which are effectively either relaxing your body (the parasympathetic nervous system) or keeping it in flight or flight mode (the sympathetic nervous system)

If your system gets stuck in fight-or-flight mode, your variability between heartbeats tends to be less and your HRV, therefore, measures lower. On the other hand, if the body is in a more relaxed state, the variation between beats is greater, meaning your HRV is higher [4]

Having a device that measures HRV can be useful to track improvements in cardiovascular fitness and to monitor stress, as well as to find out what triggers a drop in HRV for you personally (e.g. late nights, alcohol, poor diet). For athletes in particular, low HRV readings can also signify when it’s a good time to take a rest day.

However, your HRV is highly individual and can’t be compared with another person’s. Instead, you should look for trends in HRV and not get too hung up on day-to-day ups and downs.

It’s also really worth finding when and how your wearable device takes the HRV measurements. Most measure your HRV at night when you are sleeping, but for more meaningful HRV results you need a sensor that takes an average of an entire night of data (like Oura does, for example) rather than taking just one or a few points with the potential for misleading data [5]. The other option to optimize accuracy in HRV measurements is to measure yours every morning upon waking (e.g. using the Breathe app on the Apple Watch). You can also measure your HRV accurately by using the HRV4Training app and the camera on your phone.

Blood Oxygen Saturation

Many wearable health tech devices now measure SpO2, or the saturation of oxygen in your blood.

Finger-worn pulse oximeters that check if oxygen levels are dipping came into their own during the COVID pandemic, so it’s handy that a watch can do the same (some are FDA approved for this). 

Realistically though, most healthy people are unlikely to need oxygen sensing as part of their wearable health tech.

Where it gets more useful is when SpO2 measurements are incorporated into wider health algorithms — for example, Oura, Fitbit, and Samsung Galaxy watches use SpO2 as part of a suite of measures (including breathing rate or respiratory rate) to determine breathing disturbances at night. Too many disturbances could indicate the health condition sleep apnea, meaning it would be worth checking in with your doctor for a more reliable work-up.

ECG Monitors

Getting an electrocardiogram (ECG) straight from your wrist would have been unthinkable a few years ago but is now a reality with a number of latest-generation fitness trackers and watches. Some Fitbits, as well as Apple and Google Pixel watches, include FDA-approved ECG testing, which can be used to alert you if you have irregularities in your heartbeat (which might indicate atrial fibrillation, or Afib). 

As Afib is one heart condition that is more common in athletes, you may want to look for the ECG feature in your wearable health tech if you are a competitive sportsperson. 

Your Afib risks as an athlete are also higher if you [6]

  • Do multiple sports (if you are a triathlete, for example)
  • Compete in endurance events
  • Are younger (over 55s are less at risk)

For the general population of non-athletes, Afib is more common as people age, so you may also want to seek out a watch with an ECG if you are in an older age group, particularly 55+.

Although the worldwide prevalence of atrial fibrillation is approximately 1%, this jumps to nearly one in ten for 75-year-olds. Increased alcohol consumption, high blood pressure, inflammatory conditions of the heart (myocarditis and pericarditis), diabetes, and hyperthyroidism also increase risk, so these are other reasons you might want to have a wearable that can check for irregular heartbeats [7].

Temperature Sensors

Some monitoring devices regularly sense your skin temperature while you sleep and use this data to make the tracking of sleep phases a little more accurate. Changes in temperature also indicate to women where they are in their menstrual cycle and the future of this technology will likely be focused on helping women to find out when they are ovulating and, therefore, fertile.

In fact, you can already sync your Oura ring temperature day with the Natural Cycles app to give you your window of fertility each month, and in the future this feature will be directly integrated into Samsung’s Health app (slated to arrive in Galaxy Watch 5). 

Other than these distinct uses, temperature tracking isn’t likely going to be that useful to you, however. If you have symptoms and need to check if you have a fever, you will be better off using a standard forehead or ear thermometer.

Don’t Trust Calorie Counts

One thing you definitely can’t rely on from your wearable health tech is an accurate calculation of calories burned.

One systematic review found that out of 22 activity tracker brands tested, not one estimated calorie usage accurately, and the error rate across the trackers was more than 30% [8]. 

To increase the chance of the calorie counts being at least in the right ballpark, making sure you enter your age and weight will help.

A simpler calculator app like tdeecalculator.net can also help if your focus includes calories-in calories-out. However, while calorie burn can be a useful metric to think about, it’s important to not get too wrapped up in the exact numbers. It’s more important to pay attention to how exercise impacts your hunger cues, energy levels, and mood.

What About Continuous Glucose Monitoring?

I have written a separate article on Continuous Glucose Monitoring, so I don’t intend to go into much detail here 

However, a continuous glucose monitor (CGM) is becoming one of the fastest-growing sectors of health tech, so it’s important to include in any discussion of wearables.

A CGM isn’t something you wear on your wrist or finger — instead, it’s typically a small sensor you can easily attach to your skin (usually on your stomach or upper arm) at home. Some sensors go under your skin and must be inserted by a doctor. The biosensor measures your glucose level and sends regular measurements to an app on your smartphone.

You’ll unequivocally benefit from CGM if you have diabetes and need to track your blood sugar levels closely at all times. But even in nondiabetic people, CGMs may be used to detect [9]:

  • Abnormal blood sugar levels that could indicate prediabetes
  • Differences in blood sugar responses to various types of food 
  • Blood sugar responses to different types of exercise, which may inform a personalized exercise plan
  • How stress levels can affect blood sugar levels, which can help with self-awareness and improvements in stress responses
  • How your sleep patterns affect your blood sugar [10]

CGM tech is expensive and unlikely to be covered by health insurance if you don’t have a medical need. So you need to consider if you really need one and how useful it is going to be to you. 

If you have a tendency to over-stress about your health a CGM could definitely be data overload for you. Most people will naturally improve their blood glucose control by eating regular healthy meals and living an active lifestyle, without the need to measure constantly.

Does Health Tech Create Anxiety?

Some clinicians have voiced concerns that delving into health tech too deeply can actually make us too obsessive and anxious about our health. With sleep trackers in particular, there is some evidence that this might be the case.

For example:

  • A 2020 literature review identified heightened anxiety as a potential downside of sleep trackers for those suffering from insomnia, particularly if the feedback indicated poor sleep performance [11].
  • One study manipulated the sleep scores people’s smart watches reflected. When people got low scores, even if they had slept well and the read-out was a lie, they were more likely to have a low mood, increased daytime sleepiness, and thinking difficulties [12]. 
  • Conversely, those who were told they had a great night’s sleep showed better mood and functioning even if they had actually slept poorly. 

The above has led some researchers to conclude that (often inaccurate) sleep trackers could change your emotional state and concentration levels during the day and may potentially worsen mental health issues [12].

That said, there’s little solid research to suggest wearable technology as a whole is bad for mental health. Conversely, for many people, it’s a source of reassurance and comfort.

  • One large survey found that the use of wearables tended to significantly reduce psychological distress because wearables helped people take better care of their own health and feel better about themselves [13].
  • Another small survey found that wearable activity trackers were a consistent source of positive psychological benefit to almost everyone who used them, and the main negative feelings associated with wearables came about when people couldn’t use them for some reason [14].

In light of this, it’s best to only use your sleep tracker to monitor general themes in your sleep and take the day-to-day (or night-to-night) data with a grain of salt. This way, you can keep an eye on your overall sleep trends and health without over-relying on it to determine how you’ll feel the next day.

Wearable Health Technology Can Make Life Better

On the whole, it’s amazing what insights wearable health tech can bring and as long as you interpret the results with caution (and don’t use them as a substitute for medical advice from a healthcare professional) they can be a useful part of self healthcare. 

Fitness trackers can also give you a motivational nudge in the right direction when it comes to moving more and being less sedentary. 

However, if you are aware you have health anxieties and find yourself becoming a slave to your tracker or watch, it might be time to give yourself a break.

Whether you love your wearables or prefer to be health tech free, the Ruscio Institute for Functional Health is here to help with any health concerns or anxieties you may have — simply reach out to one of our functional health experts for telehealth help.

The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.

➕ References
    1. Lee XK, Chee NIYN, Ong JL, Teo TB, van Rijn E, Lo JC, et al. Validation of a consumer sleep wearable device with actigraphy and polysomnography in adolescents across sleep opportunity manipulations. J Clin Sleep Med. 2019 Sep 15;15(9):1337–46. DOI: 10.5664/jcsm.7932. PMID: 31538605. PMCID: PMC6760396.
    2. Hernández-Vicente A, Hernando D, Santos-Lozano A, Rodríguez-Romo G, Vicente-Rodríguez G, Pueyo E, et al. Heart rate variability and exceptional longevity. Front Physiol. 2020 Sep 17;11:566399. DOI: 10.3389/fphys.2020.566399. PMID: 33041862. PMCID: PMC7527628.
    3. Koch C, Wilhelm M, Salzmann S, Rief W, Euteneuer F. A meta-analysis of heart rate variability in major depression. Psychol Med. 2019 Sep;49(12):1948–57. DOI: 10.1017/S0033291719001351. PMID: 31239003.
    4. Heart rate variability: How it might indicate well-being – Harvard Health [Internet]. [cited 2023 Mar 1]. Available from: https://www.health.harvard.edu/blog/heart-rate-variability-new-way-track-well-2017112212789
    5. Bellenger CR, Miller DJ, Halson SL, Roach GD, Sargent C. Wrist-Based Photoplethysmography Assessment of Heart Rate and Heart Rate Variability: Validation of WHOOP. Sensors. 2021 May 20;21(10). DOI: 10.3390/s21103571. PMID: 34065516. PMCID: PMC8160717.
    6. Newman W, Parry-Williams G, Wiles J, Edwards J, Hulbert S, Kipourou K, et al. Risk of atrial fibrillation in athletes: a systematic review and meta-analysis. Br J Sports Med. 2021 Nov;55(21):1233–8. DOI: 10.1136/bjsports-2021-103994. PMID: 34253538.
    7. Nesheiwat Z, Goyal A, Jagtap M. Atrial Fibrillation. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2022. PMID: 30252328.
    8. Germini F, Noronha N, Borg Debono V, Abraham Philip B, Pete D, Navarro T, et al. Accuracy and Acceptability of Wrist-Wearable Activity-Tracking Devices: Systematic Review of the Literature. J Med Internet Res. 2022 Jan 21;24(1):e30791. DOI: 10.2196/30791. PMID: 35060915. PMCID: PMC8817215.
    9. Holzer R, Bloch W, Brinkmann C. Continuous Glucose Monitoring in Healthy Adults-Possible Applications in Health Care, Wellness, and Sports. Sensors. 2022 Mar 5;22(5). DOI: 10.3390/s22052030. PMID: 35271177. PMCID: PMC8915088.
    10. Tsereteli N, Vallat R, Fernandez-Tajes J, Delahanty LM, Ordovas JM, Drew DA, et al. Impact of insufficient sleep on dysregulated blood glucose control under standardised meal conditions. Diabetologia. 2022 Feb;65(2):356–65. DOI: 10.1007/s00125-021-05608-y. PMID: 34845532. PMCID: PMC8741723.
    11. de Zambotti M, Cellini N, Goldstone A, Colrain IM, Baker FC. Wearable sleep technology in clinical and research settings. Med Sci Sports Exerc. 2019 Jul;51(7):1538–57. DOI: 10.1249/MSS.0000000000001947. PMID: 30789439. PMCID: PMC6579636.
    12. Gavriloff D, Sheaves B, Juss A, Espie CA, Miller CB, Kyle SD. Sham sleep feedback delivered via actigraphy biases daytime symptom reports in people with insomnia: Implications for insomnia disorder and wearable devices. J Sleep Res. 2018 Dec;27(6):e12726. DOI: 10.1111/jsr.12726. PMID: 29989248.
    13. Choudhury A, Asan O. Impact of using wearable devices on psychological Distress: Analysis of the health information national Trends survey. Int J Med Inform. 2021 Dec;156:104612. DOI: 10.1016/j.ijmedinf.2021.104612. PMID: 34649113.
    14. Ryan J, Edney S, Maher C. Anxious or empowered? A cross-sectional study exploring how wearable activity trackers make their owners feel. BMC Psychol. 2019 Jul 3;7(1):42. DOI: 10.1186/s40359-019-0315-y. PMID: 31269972. PMCID: PMC6607598.

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