Six rules to get the most out of fitness & wellness tracking

Self quantification is the trend that just keeps on going. There's an ever-expanding world of wellness wearables and fitness trackers targeting consumers with shiny promises of the personal value to be had if they monitor stuff like their heart rate, activity and sleep -- from smart watches, bands and rings, to smart scales, CGMs (continuous glucose monitors) and more.

Some of the fitness & wellness devices marketed to consumers have features that claim to be able to detect medical conditions or disease risks. Apple, for one, has made much of its FDA-cleared ECG (elctrocardiogram) and atrial fibrillation (irregular heartbeat) detection features over the years.

But medically cleared features remain the exception in the space. Most of the data being output by category products hasn't been reviewed by regulators so it can be tricky for consumers to know how accurate/useful these "personalized" assessments really are. And what, if anything, they should make of all the "general wellness" metrics and "health" scores appearing in their apps.

Fortunately, there are some solid rules of thumb to get the most out of produces in the fitness and wellness category without losing sight of their limitations.

Researchers in the field we spoke to for this article are also quietly optimistic that tenacious personal health monitors, with their ability to go the distance by producing a longitudinal view of what we're up to, will, down the line, be able to deliver on the promise of preventative healthcare and help many more of us step away from bad habits that risk a long, slow slide into chronic disease.

We're also told there's lots of research being done to extract better signal out of noisy real-world data, including by using AI. And if we had to make a bet on where the category is headed, we reckon in-ear monitoring looks particularly interesting (see the last section of this article for more on this) -- after all, rumors continue to suggest Apple is looking at adding health features to its AirPods -- so we're generally bullish on the longer term direction of travel for consumer health tech. But, as it stands, there are still some risks and pitfalls to avoid.

Did you find a fitness tracker under your Christmas tree this year? Are your New Year resolutions to be more active making you wonder if it's worth investing in a wellness wearable? Read on for help to keep your head amid the hype and find the best signal in noisy data. Finally, we also take a peek forward at where this evolving category could be headed...

Rule One: Mind the hype, read the small print

The cardinal rule is to approach all fitness/wellness products with a critical eye -- and be very wary of stuff that overpromises. In short: Read the small print, not the marketing.

Getting you to upload your data might be the main aim of a new and unproven product, especially if it's making eyebrow-raising claims of accurately assessing your risk of almost every condition/disease under the sun. Using such a product is likely to help someone else a lot more than it helps you.

Case in point: A pitch for a smart mirror that was being shown off at CES this year sure raised our blood pressure: NuraLogix, maker of a device it brands as a "MagicMirror", claims the product can produce all sorts of vital/physical "measurements" and "health risk assessments" off of a 30-second facial scan -- including blood pressure, BMI, Type 2 diabetes risk, 10 year cardiovascular disease risk, hypertension risk and even anxiety and mental health risk, among a list that's too long to reproduce here in full. Per its press release, it's using "patented Transdermal Optical Imaging" tech -- which it dubs "a novel form of Remote Photoplethysmography (rPPG)" -- and proprietary AI to produce "accurate health data" via lingering selfie.

However, if you scroll a further down the company's PR you'll find a small-print disclaimer at the bottom of each page -- which states: "In the United States, this product is for Investigational Use Only. The performance characteristics of this product have not been established." (Rough translation: Those "accurate" measurements of health/vital signs/disease risk assessments we mentioned earlier are of unknown accuracy; this is not a diagnostic medical device.)

A year ago, NuraLogix claimed to be applying for FDA clearance, per a colleague's report on an earlier iteration of its selfie scanning tech which was being shown off at CES last year. But, evidently, it hasn't managed to get sign-off on any of its myriad "health solutions" yet, despite the heavy hype in its marketing.

Maybe this company's smart mirror will gain regulatory clearance for some functionality in future. But hype-first products like this, which arrive in the market prior to their "performance characteristics" being "established" -- accompanied by flashy marketing that touts multi-faceted utility -- just don't pass the sniff test.

There can be a "blurring of the lines" that enables unsubstantiated health claims to be made, or at lest implied, by device makers, says Ahmar Shah, a senior research fellow in the University of Edinburgh's Medical School. "Usually the reason people are able to get away with this is they market their device as a 'wellness' device, or say they're doing 'wellness monitoring'. And when you do that then it's not considered a medical device," he tells TechCrunch.

This can lead to sweeping suggestions of health utility that haven't actually been substantiated, so long as device makers carefully frame and/or caveat their claims. "It's an unregulated environment. You will see good stuff -- but you will also see stuff that's just more marketing than some solid evidence base," he warns.

If the line blurring continues, pressure may grow to bring "wellness" kit under formal medical device regulatory frameworks -- and at least require a certain standard of proof for any claimed health benefits. But, for now, the game -- and the claims -- continue.

Of course companies are always hungry for data to feed their product development, so they can turn out better, more effective products. But when it comes to consumer health tech, exaggerated marketing claims are a particularly dubious tactic as they may trick people into handing sensitive information to a commercial entity and getting nothing much in return (well, except the risk of their personal data being misused -- see Rule Six).

Another growing wave of startups in this space are devising and marketing "general wellness" products that are getting even more up-close-and-personal with the user as tracking hinges on wet testing samples of bodily fluids to serve "personalized" insights to an app. (See, for example, Vivoo's urine analysis for suspected UTI testing or vitamin deficiency detection; or Zoe's glucose monitoring for metabolism analysis and stool sampling for quantifying gut microbiome, to name two.)

While such products look novel (and may have promise), there's a risk of unproven assessments misleading users about their health and/or making them anxious -- especially if people assume outputs are more meaningful than they actually are. At this highly experimental end of the tracking and quantified self category, reading both the small print and any research product makers have published to support their claims, so you can make your own assessment of their credibility, is a must.

Bottom line: Companies exploiting health concerns to grab people's data is not a good look but it happens a lot. (Think 23andMe's genetic testing as the classic example -- a category veteran whose marketing is suggestive of some general health utility from information it will send you if you send it your spit in a tube so it can extract your DNA but whose small print disclaims its tests as diagnostics and denies they're capable of producing individual disease risk assessments. So, really, you're paying to donate your genetic data. With all the risk that entails.)

A generous interpretation in cases where product makers may be promising more than they can prove is that those behind the data grabs genuinely believe they're onto something that will end up being useful in the future. They just need to do more R&D. So this is about getting (your) data to further their research. And, sure, a lot of 'innovation' happens that 'backwards' way round. But, in the meanwhile, since product outcomes aren't robustly verified, the companies behind these experiments should be making it crystal clear to users they're the guinea pigs.

As noted above, NuraLogic's small print concedes its smart mirror is for "Investigational use only" -- most likely a reference to its own product R&D, frankly. But if you failed to read the small print and have ended up the (unhappy) owner of such an unproven device and it's too late to send it back -- and now it's churning out less than ideal assessments of your vital signs -- definitely don't panic. The data is probably junk. But, remember, (professional) investigation is always an option -- see: Rule Five.

When it comes to contactless health monitoring -- such as the use of cameras (and selfies) for tracking biomarkers like heart rate or blood pressure, as with the aforementioned smart mirror -- Shah's view is signal quality looks like a major challenge, even before you consider the overarching difficulty such products face of needing "lots of good data" to train AIs to perform all the claimed health detections without their outputs being riddling with bias and inaccuracies.

"Engineers are working on trying to come up with better algorithms to counter those signal quality issues etc. But I suspect -- my hunch -- is that these contactless [approaches] will be hard," he suggests. "Just because they often depend on the ambient lighting conditions and you have less control. So the less control you have of the environment that you're measuring, generally, you can expect it will be more hard to get a reliable measure."

"The deployment of AI in health requires quite a few years," predicts Danilo Mandic, a professor of machine intelligence in Imperial College's department of engineering -- also pointing to problems with bias and other data quality and accuracy issues linked to recording noisy, moving targets like human bodies.

There are, he suggests, no AI-powered shortcuts to be had here, whatever the hype may imply. Instead, device makers will need to access proper background research and biophysical groundwork to support the development of quality measurements and credible AI models. "The problem with AI is, at least, many people just say give me data and I'll do something -- it doesn't work like that!" he warns. "It requires domain knowledge and biophysics models.

"In a way, there's no replacement for 'banging your head against the wall', as it were, for many years, going into uncharted territory."

Rule Two: Pay attention to the instructions

This rule sounds super basic but it's actually fundamental. Because if a device contains any features that have been cleared by medical regulators they will only have been demonstrated as effective and approved for the specific use-case and usage protocol. Stray from the required protocol and you're not going to get the benefit of the verified assessment -- which, doubtless, got given prominent positioning in the product marketing. Indeed, you might not even get an output. (And, if you do, it's probably not going to be reliable if you failed to follow the instructions.)

So when, for example, you use the Apple Watch to access its ECG function and it tells you to try not to move your wrist and/or make sure the watch is snug on your arm when you make the recording -- and when it informs you the feature never checks for heart attacks -- you should really listen to these essential details.

You also need to pay attention to usage instructions and the specifics of what such a regulator approved feature does (and doesn't) measure to avoid the risk of being misled (either by bad data or your own incorrect assumptions).

Again, in the case of the Apple Watch's AFib notification feature, the clearance received from the US Food and Drug Administration (FDA) is for users who are "22 years and older with no prior history of the condition", per Apple's website. If you fall outside those limitations the level of efficacy the company was able to demonstrate to the regulator won't apply.

Device makers offering products with regulator approved features will typically require users to read and agree to dedicated T&Cs before they can access the specific function -- exactly in order to instruct on correct usage. But we all know how much attention the average tech user pays when they're faced with yet another screen of small print standing in the way of the thing they're trying to do. So it pays to be reminded to actually focus on the detail.

A product's standard user manual should provide details of what has and hasn't been regulated, per Imperial College's professor Esther Rodriguez-Villegas, director of the university's Wearables Technologies Lab and founder of a sleep tracking medical device startup called Acurable. So her concise advice is: Read the manual.

"What the manual will say is how that the [device] needs to be used for that [regulated feature] to be valid," she explains, noting the documentation should set out any accuracy limitations related to usage. "It might say the result should not be taken for any clinical diagnosis," she also warns. "There are actually devices that have been regulated and when you look at their user manual they do say that. So that's why none of these devices should be used without looking at the user manual. Or having a clinician recommendation -- in the sense that the clinician would have read the manual."

Another signal she suggests consumers may be able to factor in is to look for instances where public healthcare services may be adopting consumer devices, such as to provide to patients for home monitoring. "If the NHS is using them -- genuinely using them, in clinic, not [having] a clinician to do marketing for them -- so if there are hospitals where this [wearable device] is how they are checking on patients -- then it's a different story," she says. "Because I can guarantee you, you don't get to the NHS easily. There is a lot -- a lot -- of scrutiny."

The existence of any features on a consumer device that have been reviewed and signed off by a medical device regulator as effective for a specific purpose is a credibility signal in itself, too, to a degree. Generally speaking, if a product includes such features/functionality it's a positive sign about the company behind it -- meaning it's put in the time, effort and resources to demonstrate to an expert public authority that its product can meet a standard and perform as claimed.

Applications for regulatory clearance are a major undertaking -- and all the work involved in obtaining sign-off can take years, plural. So it's another rule of thumb when shopping in this category to look for products with approved features. It's a mark of commitment that you may be able to use to filter between different device makers.

That said, it's important to remember that regulatory vetting is limited. It only covers whatever specific function the feature was approved for. Whereas consumer health tech products may combine one or more cleared features with (many) others that haven't been reviewed for efficacy by a public standards body -- meaning, overall, most of the functionality hasn't had to prove its utility.

Consumers shouldn't lose sight of these distinctions and just assume all outputs on a particular device are credible because the FDA approved one of the features. An increasing number of products targeting consumer demand in the health/wellness category are crossing the streams by combining some evidence-backed functionality which has gained a regulatory stamp of approval, with far more features that haven't been vetted. However legit/fancy/impressive these other bells & whistles may seem their output is unproven and may be totally inaccurate.

"A lot of the wearables that are in everyday use are consumer wearables. They're specifically advertised as 'wellness and fitness'. So they don't have to go through medical device regulation," explains Dr Gerard Cummins, an assistant professor in engineering at the University of Birmingham who also heads up its Medical Microsystems lab. "Medical regulation is there for a reason. If you're making a device and you're marketing it as a medical device it needs to have a higher level of quality -- in terms of accuracy and precision and safety -- because people are going to be making life changing decisions based on that. You wouldn't make a life changing decision based on something that your Apple Watch says just in general."

In the case of a regulator cleared feature, users may have confidence that, if used correctly, the tech can do what's claimed. But there will still be a margin of error and the possibility of the device failing to record a strong-enough signal to serve a good result every time. Still, as the user, you're in charge of controlling usage conditions to ensure the best recording possible (so we're back to the importance of following instructions).

It's also worth taking care not to get tripped up by certain category marketing tactics that can make it sound as if a product has undergone regulatory review when, in fact, the reference is more tangential -- to only a component of what's being used in it, say, rather than the main output they're trying to sell you.

For example, over the last several years we've seen a wave of startups building fitness & wellness businesses by commercializing CGMs (continuous glucose monitors). This is a type of sensing hardware that's been cleared by regulators for use in diabetes management. However what these startups are selling is something else -- often their services are marketed as being for fitness/wellness support or metabolic tracking.

The algorithms and software they've developed, to process and present the signals obtained via CGM, so they can offer "personalized" insights for their (non-diabetic) users, has not been approved by regulators. So while the presence of "medical grade" sensing hardware might make these products seem credible, it's not applicable for what they're using the tech for. The only benefit that bleeds across is that users of these metabolic tracking services can at least be confident it's safe to apply the (partially invasive) CGM sensor to their arm (again, though, carefully following instructions is a must!).

Bottom line: It's important to pay careful attention to what a tracking product is and isn't; and make sure you understand what it does and doesn't do to avoid being misled.

At the end of the day, it's either a diagnostic medical device or it's not. And most consumer tech is not, regardless of how much its marketing may be banging on about your health.

Rule Three: Focus on trends, not data points

There's a big difference between a snapshot and a video. The same is true when it comes to the outputs of fitness trackers: Single data points served up by wearables probably aren't going to tell you anything useful, not least given the potential for errors and inaccuracies. But lots of snapshots over time can stack up to a story about what might be going on with your body that's worth listening to.

The way to get the most out of noisy, imperfect data from wearables is to let the tech establish a baseline for you and then monitor this to see how your metrics are moving. In other words, focus on trends, not individual data points. For example, a resting heart rate that's trending lower over time may say something positive about your lifestyle. Ditto the reverse.

Apple's smart watch can do this step for you by tracking and serving up what it calls "health trends". So better devices will aim to do this leg work for you -- you just need to pay attention to the direction of travel over time.

“If you start establishing a baseline of yourself on one of these [tracked metrics], let's say your resting heart rate, and you see how that changes over time, this is of value because if there is an error -- in the calculation, in the algorithm, in the sensor, because it's cheap -- the error will be there constantly. So, somehow, the fact that you have a lot of data about yourself, longitudinally, I think allows you to start building something quite useful,” argues Cecilia Mascolo, a professor of mobile systems at the University of Cambridge.

“These devices, for as little precision they can have, they can give you years of quite fine grained data. And if you talk to a neurologist even just the information about your sleeping pattern, when you go to bed, when you wake up, is already very indicative over time. So this to me is the most tangible, simple example that I give to say, well, okay, yeah, we're still working on the precision of this stuff but the data is flowing. And if you establish -- especially if you establish your own baseline and you see how this changes, what the trends are in your own data -- I think this is of value. The longitudinal aspect, I think, is very important.”

"There are advantages with longitudinal data," agrees the University of Birmingham's Cummins. "If you go to a GP, you're just getting a snapshot of your health [maybe] once every two years, whereas [with wearables] you have this rich, longitudinal trend data. The accuracy of individual data points may be up for debate but the trend itself would be quite useful. So you get more of an overview of how things develop in your body over time."

A number of researchers we spoke to for this article highlighted how the wrist, especially, is a poor place for measuring heart rate given how much we move our arms around in daily life. Blood oxygen levels measured by optical sensors applied to human skin are also notoriously inaccurate -- especially on darker skin. So consumer wearables will undoubtedly capture poor quality data sometimes or even a lot of the time. But a baseline that's increasing or decreasing (or even just staying stable) may still be able to tell you (or your doctor) something useful. Whether it's a trend in your resting heart rate, total time asleep or respiration.

The big promise of trackers is of course exactly that they keep a record, and let users access a longitudinal view of bodily signals, which creates the possibility of spotting changes that might otherwise be too subtle/gradual for a person to notice. So -- tl;dr -- lean into your trends.

Having trends surfaced handily in an app, which may also be encouraging the user to track various aspects of their lifestyle and activities, creates the opportunity for people to join the dots between changes in their data and their habits. This is about helping users get a handle on factors under their control or influence which might, possibly, have health implications.

Let's say your app notifies you about a drop in your average resting heart rate. Did you starting doing yoga to combat stress, or make the effort to clock up eight hours of quality sleep (not five), or start drinking less alcohol? Maybe you can link a directional shift in your data with a particular lifestyle tweak and make an intelligent guess at what's working for your health. That's the power of a good tracker.

Rule Four: Tracking the basics can be powerful

While there's a growing number of fitness/wellness products that propose to let you track more complex/less well understood aspects of biology -- such as metabolism, or the gut microbiome -- or which claim to be able to quantify more nuanced metrics like heart rate variability (HRV), or offer to segment your sleep stages (deep, REM, core etc), the value proposition for the average consumer of trying to self-quantify at such granularity is: A) not clear-cut because so much of what's going on with human biology at these deeper levels still isn't well understood; and B) probably pointless (for now), as our current gadgets and gizmos aren't able to capture accurate enough data for such tracking to be meaningful.

So the rule here -- for the general consumer -- is that the cost-benefit analysis of shelling out for unvalidated deeper self-quantification (or, indeed, a full-body 'scan') probably doesn't stack up yet.

On the flip side, where the value is more clear-cut is in tracking simpler stuff. Tracking basics like your movement (e.g. steps) and sleep (i.e. total time asleep) might not sound super exciting these days but such self quantification can be surprisingly powerful and positive for your health. Because we know that staying active and getting enough sleep are great lifestyle interventions that can absolutely improve our well-being and foster better health.

As the University of Birmingham's Cummins points out, studies have shown wearable devices can be positive for behaviour change -- because of the "feedback loop" they set up between the user and the device. ("They see their activity increasing and might notice a trend in, for example, their cardiovascular health over time. So there are benefits," he suggests.)

Trackers that encourage users into being more active, such as by cheerleading when you hit a daily step goal, or nudging you to get more hours of quality sleep by gently suggesting you wind down in the evening, can thus have clear value -- even if these features may seem pretty unremarkable at this point in time, a little shy of two decades since the advent of the humble Fitbit. But forget fancy bells & whistles; when it comes to health potential, simple stuff can be powerful.

That said, it's really the effectiveness of the product experience -- in inspiring and driving positive change for an individual user -- that's the important aspect here, since the data itself (step counts, sleep hours etc) is unlikely to be entirely accurate either. (To wit: A 2020 study published in the journal Nature and the Science of Sleep which looked at eight consumer sleep trackers, including the Apple Watch, Fitbit Ionic, Oura smart ring and Whoop band, found what the authors called "a remarkably high degree of variability" in the accuracy of commercial sleep technologies -- so even seemingly simple metrics should be taken with a pinch of salt.)

Different individuals may prefer different wearable form factors and/or app approaches to support them in being more active and getting adequately rested. So assessing product value is necessarily personal and subjective. But, again, the rule of thumb is so long as a tracker helps you get your steps and sleep trending in the right direction that's really the point (back to Rule Three)

Most wearables do also include heart rate monitoring as a basic feature these days. One researcher we spoke to questioned the value to the average consumer of tracking this metric, i.e. outside a specific pathology-based reason for doing so (and the use of a chest strap which is typically a more accurate way to measure it). But most saw value in having a read of it -- including because a longitudinal view of resting heart rate can be a springboard to quantifying the healthiness of your lifestyle.

"The heart rate, the resting heart rate, gives you a measure of your fitness," says the University of Edinburgh's Shah. "If you're stressed, if you don't sleep well, your resting heart rate [may increase]... There are resting heart rate ranges for if you're physically very fit -- like athlete-level -- or average or below average. And they make sense."

But what about tracking more nuanced biological metrics? A growing number of fitness devices will now calculate HRV (aka, heart rate variability) -- a measure of the time between successive heartbeats that's supposed to provide information on the interplay between different branches of the nervous system (the sympathetic and parasympathetic), and the functioning of the system as a whole. Which, in turn, may provide indicators of bodily stress. (Interestingly, the Apple Watch tracks HRV but doesn't surface the metric in the Health app overview; you have to go digging into the heart folder to find it -- which suggests the company isn't convinced of its general utility quite yet.)

For a general consumer, it's fair to say the utility of tracking HRV is less straightforward than monitoring heart rate as it's a sensitive, highly individualized metric that's harder to interpret -- whereas there are established ranges for resting heart rate that are considered healthy, as Shah notes. (And also target heart rate zones you may want to aim for for different exercises and/or exercise intensities.)

HRV scores are complicated by there being different methods of calculating this metric, too. Some devices may continue tracking HRV during sleep, while others only track during waking hours. So different devices can produce distinctly different scores/ratings for it -- further confusing the picture for consumers when it comes to knowing what the metric might be telling them.

If you're a pro athlete focused on pushing your edge performance there may be some value in tracking HRV as a way to measure stress and recovery. But -- equally -- such a user may well need more structured (and manual) HRV tracking, with measurements taken at specific points in their training schedule, rather than the continual background tracking that's typically offered by consumer devices that offer an HRV rating/score.

Given all the uncertainty, apps that score/rank HRV for a general consumer risk being misleading, in our view. Again, trends may help -- so letting the tech establish a baseline for the metric and tracking any movements up or down -- but this is still a data-point the average consumer probably shouldn't lose too much sleep over.

"Nobody can say with authority that if your heart rate variability goes below this number or that number then something wrong is happening," agrees Shah. "These are things people are still exploring. It's not completely clear."

"The bottom line is that, today, [some biomarkers tracked by wearables] might not be useful for an average consumer," he continues. "But I think they could become useful once we establish which exact metrics are valuable -- and, also, how do you present the information? I mean, all these are open questions at the moment. Companies like Fitbit, Apple -- these are the big players and they're still innovating."

"All these things have potential value," he adds, pointing to the link between lifestyle factors and people's risk of developing chronic diseases. "The reason I'm saying potential is there are indications from research studies that some of these [biomarkers], like heart rate variability... might have value. For example, if it decreases a lot then it might be a sign of something like your body is stressed. But the challenge we have is that conducting these type of studies is incredibly hard."

The category promise is that by tracking more and more bodily signals we'll generate the data that helps make the correlations that drive preventative medicine -- so the hope is the tech will get better and better at nudging users towards healthier lifestyles, including by being able to detect possible health problems earlier than our reactive healthcare systems currently do.

But while it's now incredibly easy for consumers to get a whole host of data about themselves, if they buy into the tracking trend and strap on a wearable or two, the rock solid proof that there's value in collecting and processing all these signals isn't there yet -- all we have for now are "early indications", as Shah puts it.

Further along the complexity axis, the value of the tracking tends to be even less clear. To wit: There's a growing number of startups offering to sell "personalized" advice based on consumers testing/tracking their bodily fluids -- to measure things like blood glucose swings or the make-up of your gut microbiome. At this highly experimental end of the market, unless you've got a particular, personal motivation to dig deeper -- say you suffer from recurrent UTIs or have concerns about fertility and haven't found traditional healthcare routes pleasant or helpful; or you've got a problem with weight management and conventional approaches to diet and exercise haven't worked for you -- there's probably a lot more uncertainty than utility to be had from this sort of tracking.

Certainly, it's vital to keep in mind that any value to such experimental tracking is, at best, speculative. So while the sampling and testing processes involved may lend some of these products an aura of scientific credibility, it's important to keep a cool head. Because when the science is so open there may not even be a confirmed understanding of the bit of biology they're offering to quantify -- making any interpretations of your results, at best, informed guesswork. (While novel techniques to speedily analyze your test result remotely, rather than requiring you to mail your sample off for a lab test, could introduce inaccuracies at the source.)

The main beneficiary of such complex and -- as yet -- unproven trackers is thus likely to be the company that's getting your money and/or data to build a business.

By serving up "personalized" test results they're positioning themselves to flog their users quasi treatments, too -- whether it be diet advice or vitamin supplements, or even a consultation with a qualified medical professional (for a fee) -- cross-selling other products and services to address user-specific needs their proprietary tech has apparently picked up in your data/bodily fluids (but without any requirement to show evidence that would convince a regulator). It's a dynamic that looks extremely convenient for drumming up customer demand. So there's an obvious risk of conflicts of interest.

Anything this experimental and unproven generally falls into the 'caveat emptor' category. Unless you have a specific concern -- and are willing to take a punt on exploratory self investigation -- you're likely better off not wasting your money.

Rule Five: Worried about your data? Take it to your doctor

If you do find yourself worrying about something your tracker is flagging up then don't be afraid to book an appointment with your a doctor and ask for an expert opinion. It's a golden rule.

While you might think healthcare professions get a sinking feeling when patients arrive armed with a PDF of their wearable data, the opposite is true for Dr Hemal Shah, an NHS GP who is also medical director of the digital healthcare platform, Dr Dropin. “My personal thing is I encourage patients to tell me -- because it does make a difference. It just gives you more information on someone," he tells TechCrunch. "Certainly if you've got symptoms, and you have whatever condition and you've noticed the trends changing [in your wearable data], it is useful to tell the doctor because it can indicate different things going on. So more information is always better.”

He also points to the value of doctors being able to see longitudinal data they otherwise wouldn't -- at least not outside a long term hospital admission scenario.

Trackers can fill in gaps in patients' memories, too -- offering an available record of whether you've had decent or not so decent sleep over the last several months, for instance, whereas your own memory of how much sleep you got might be more hazy.

Additionally, consumer trackers have the advantage of just being there, on your person/in your proximity, where they're in a position to record some data -- say in the middle of the night when you woke up with heart palpitations and could reach for the ECG feature on your smart watch -- information which, for all its potential fuzziness, is going to be better than your doctor having no intel at all, per Dr Dropin's Shah.

“There are moments — especially with the Apple Watch and some of the other devices — I definitely do encourage patients to take more readings," he says. "Its ECG monitoring, it's not a medical device, but it gives you an indication of what your heart rhythm is.

"I recall patients who would have episodes of feeling palpitations and their heart going really fast. And one of the things we really want to know is the electrical activity in the heart. And [trackers like the Apple Watch with an ECG feature are] able to give a snapshot of what it was like at that moment in time. And so we definitely do encourage it."

"I certainly refer patients to cardiology specialists who do look at it and will actually make a diagnosis based on that information if it all fits the picture of what they expected to see," he adds. “If someone has palpitations and they have them very infrequently they may last a few minutes. What you can’t do is you can't get to a proper ECG machine or a medical grade machine at that time, and it's impossible to wear that machine all the time. So it allows you to recognise abnormalities on your watch and take a bit more control over things.”

There may be a risk that doctors' time could be wasted unnecessarily if lots of people start booking appointments because of stuff their wearables got them worried about. But Shah says fewer patients than he'd expected actually bring in tracker data. So far, in his experience, the rise of wearables and the quantified self movement hasn't added to the workload burden on traditional healthcare services.

Indeed, he flags lower usage of wearables among the elderly -- as he reckons there could be greater benefit to this sort of passive monitoring for frail populations -- suggesting more adoption of the tech among seniors could drive bigger public health benefits.

What about the risk of all this tracking triggering unnecessary health anxiety for some users, such as people who may be prone to hypochondria?

“I think it does sometimes add a bit of anxiety when they see something abnormal [in their data]," he responds on the anxiety point. "But I also believe that when they speak to a clinician that anxiety dissipates, or they get taken seriously, or they have further tests and then it’s all absolutely fine.”

So, again, the rule here is simple: If something in your data is making you worried, grab a download and take the concern to your doctor.

Rule Six: Don't forget about privacy

In the rush for consumers to take a personal interest in their health and shell out for tech to track their bodies and activities, it can be easy for people to forget that the data being captured, stored and processed -- and potentially shared with others -- is highly sensitive personal information.

“The signal is very, very private," warns Cambridge University's professor Mascolo. "We think imaging is private. But what about audio? What about your heart? Your heart signal is a unique fingerprint. So if we start sending everything back to central server, that's a bad thing. It could lead to unwanted exploitations.”

Consumers should carefully consider who they may be handing their private health data over to before they strap any device on. Some companies may be considerably more credible than others when it comes to claims of respecting privacy. Look for clear and prominent statements about the personal information they intend to collect and what they will do with it. Companies whose privacy policies aren't clear, or leave you confused, are best avoided.

Where your information is being stored and processed may also be important, given there can be big differences in legal protections for personal information depending on where in the world the data is being handled.

Also consider business model. How is the company behind the tracker/service intending to make money? Does their approach look sustainable? Some free-to-use period tracking apps, for instance, have been found trying to monetize their software by plugging user data into the online advertising ecosystem -- which is obviously horrible for user privacy. (For example, a few years ago, period tracker app, Flo, settled with the FTC after allegations it had shared sensitive user data with ad platforms despite promising users it would keep their information private.)

Even if a tracking product maker's business model looks legit, given the sensitive nature of the data routinely being collected and processed you should proactively consider the risk that your information could be breached and what an accidental leak might mean for you. (The breach last year of ancestry data held on millions of users of genetic testing service 23andMe is instructive of the high stakes for getting involved with quantified self tech.)

Ultimately, consumers wanting to tap in to tech and services in this health-adjacent fitness & wellness category will need to weigh up the utility they believe they may gain from whatever tracking is offered with potential risks to their privacy if their information gets misused or is not kept secure.

Business models that are selling self quantification/tracking itself, either in the form of hardware and/or a subscription service, may generally look more credible than those which rely on offering a free product to scale usage and amass data. But lots of companies in this space are also using customer data for product development and wider research and, given the sensitivity of the information involved, privacy questions and considerations come with the territory. So it's important to stop and proactively consider the risks.

"The problem is that in order to develop algorithms, a lot of these companies are actually collecting personal data," warns Imperial's Rodriguez-Villegas, raising concerns about the extent of data collection by consumer devices who may be hoping to use the info to develop a medical device. "In order to use the device, the first thing that is requested from people -- I mean, this is even after having paid for the device -- is to click on the box saying they 'agree' for this data reuse... [that their] data could be shared with partners or with collaborators."

Even if you're the sort of person who's happy to donate even sensitive personal data for speculative commercial research -- say, for the possibility of future upside for humanity if your data can support research into certain medical conditions and diseases -- at least look for product makers who make it clear how they want to use your information; and, ideally, ask for consent to use your data for research.

Companies operating in the health/wellness space that make an upfront pitch for data for research, and provide specific details of what and how they want to study, are more likely to be doing credible research, too.

In recent years, a lot of femtech startups have popped up, touting novel wellness products which rely on women's data to power predictive algorithms. Many make a point of pitching potential users on helping them close the female health data gap, given how medical research has historically focused on male subjects. You might feel your values align with such a mission -- so great, it could be a win-win. But, even so, always read the small print and check you're happy to support the kind of research they say they plan to do.

Looking ahead: Where next for wearables?

An interesting confluence of factors we've touched on in our Six Rules could end up shaping the next big evolutionary leap in wearables -- namely this trio: Accuracy issues; privacy concerns; and a push for greater efficiency of biomarker data processing, including to allow for more powerful software to be housed in smaller physical devices we may carry on our person. (And -- yep -- this is where the promise of health-monitoring "hearables" (or "earables") comes in.)

Imperial College's Mandic, who says he was the first to outline an "in-the-ear recording concept" (in a 2012 paper on "user centered and wearable brain monitoring"), highlights deep learning work he's undertaking to extract "clean" biomarkers from "very noisy" environments using models that are "computationally cheap to run", as one of his papers puts it. So the hope is for greater processing efficiency will allow for smaller types of devices to become trackers.

"The 'corr-encoder' and other models we do and are proud of don't require much power," he tells TechCrunch. "They can be implemented on microcontrollers, on edge devices, or we can stream data using Bluetooth and process them on smartphones -- we don't require huge servers."

"We need to move away from those brute force approaches [with AI] -- 'just let me add more layers in my neural networks' -- to basically thinking more, including domain knowledge and working towards smaller, much smaller, models which can work on microcontrollers -- even on the earbud," he suggests, adding: "My current model basically works directly on the earbud."

Another interesting possibility here is that privacy concerns and (AI-aided) efforts that are gunning for more efficient signals processing could conspire to drive each other. The University of Cambridge's Mascolo believes privacy concerns could encourage development of commercial AI models that are designed to live and work on the user's device, avoiding the need for sensitive health data to be uploaded to the cloud.

“We can do things on device. But we need to find the right business model for this," she suggests. "It might be that the business model is privacy — and new devices allow you to to do this. Companies are possibly still exploring if there is a privacy-based business model."

"The first step would possibly be the generation of [AI] models from data that is collected in large scale and then perhaps the pushing of new products that have these models scaled down to on-device apps on your phone and they use your own data but the data is not sent any further. I think that is very achievable,” she adds.

The privacy advancement in this scenario would mean users don't need to bare their raw biological signals to any third parties; the biomarker processing could just take place on their device. (And Mascolo also flags the potential of machine learning techniques like federated learning to further support privacy-preserving processing of wearables' data.)

There would still need to be a pool of users willing to share data for models to be developed in the first place -- but she likens this to how, during drug development, tests of novel pharmaceuticals may cause side effects in test subjects that can be avoided in the final product. (So once a fine-tuned AI model is put on device the wider user population wouldn't have to submit to the "side effect" of losing their privacy.)

“I think we're getting to a stage where privacy and efficiency are driving the solutions that we want to see,” she adds.

Returning to hearables, Imperial's Mandic reckons health-monitoring in-ear devices could be a commercial reality in as little as "two to three" years' time.

"It's been 10 years since [my paper]. So for the first five years I was struggling to convince people that you can record from these canals. The next five years... many companies [were] set up and failed... The time has come now that things are bit more mature so I expect myself and maybe some bigger players to come up with something," he suggests.

"Clearly, if the current wearables were that good then we wouldn't be looking for anything else but they're not," he goes on, adding: "With the emerging e-health [movement] we need reliable devices which can be used to monitor people at home."

In-ear devices have an edge over wrist- or finger-based wearables for accurately measuring certain bodily measurements, per Mandic, as the ear canal doesn't suffer the same "vasoconstriction" effect as outer skin -- a phenomenon that can cause accuracy problems and bias for optical measurements performed on the wrist or finger (so bad news for smart watches and smart rings).

The head also offers a relatively stable location to perform measurements of biomarkers vs the arm/hand, which are more likely to be moving around a lot. Plus, as Mandic points out, you can wear earbuds for an extended amount of time. (Indeed, many consumers already do.) So in-ear-based tracking looks exciting for getting better signals consistency from wearables.

The University of Cambridge's Mascolo is also working in this area. Her research includes looking at "earable" tech for fitness and vitals signs monitoring -- using an in-the-ear microphone to monitor activity and heart rate in order to proxy VO2 Max. (VO2 Max is a measure of cardio or aerobic fitness which some existing consumer wearables, like the Apple Watch, already offer to estimate, based on tracking users' heart rate and movement. Although, as with other more nuanced metrics (like HRV), the accuracy of current-gen trackers' VO2 Max features is questionable.)

The gold standard VO2 Max test requires a person to attend a specialist center and undergo intense physical exercise while wearing a mask hooked up to a machine that measures how much oxygen they're breathing out vs in. So the test is usually only undertaken by athletes. Whereas wearables offer the chance for many more people to track their cardio fitness. But it's only going to be really meaningful if the accuracy of these proxy measurements steps up.

Beyond interesting-looking potential for in-ear monitoring, and the possibility of developing more privacy-preserving tracking, there's a notable trend already for consumers to get involved with more intimate/invasive types of tracking. The University of Birmingham's Cummins, for one, predicts further growth here -- suggesting we'll see more activity around these sorts of "chemical sensors" in the coming years.

He posits that the adoption of CGMs for fitness/wellness (and/or metabolic health) tracking is "the first sign of a shift" that's taking consumers beyond wearables with "physical sensors" to products that feature "'chemical sensors' in the devices". The goal is "having a richer data set on what's actually happening within the body", he says. "Not just looking at heart rate, lung capacity, activity -- it may be looking at glucose spikes, or cortisol for detecting stress, things like that."

So, on some level, the demand for chemical trackers may reflect a sense of frustration with the limits of what sensing wearables have been able to read through our skin.

His own research spans so called "ingestibles" -- novel devices that aren't worn on the body but swallowed; allowing for built-in sensors to get a read on what's going on internally, in a user's digestive system. It's a concept that could also push tracking to new depths. (And even, potentially, be used to deliver drugs in a more targeted way -- moving from tracking to treating.)

"The capsule endoscope would really be the first ingestible but there are limitations to those devices, in terms of the quality of the diagnosis, because you're just using an optical camera. So what we're doing in my lab is we're looking at either trying to improve the accuracy of these devices by integrating additional sensors," says Cummins. "We're looking at different form factors that you can swallow that would give you data about your gastrointestinal health -- or they could potentially be used for targeted delivery of drugs as well."

More generally, he suggests wearables and fitness trackers are at an "inflection point" -- with some devices starting to be used in hospitals and traditional healthcare settings, working towards the big vision of preventative health. He also flags research that aims to see if longitudinal monitoring can help detect the point at which a healthy person might be developing an illness. Plus he emphasizes the foundational trend of consumers proactively tracking themselves in a bid to make positive behavioral shifts and shrink their risk of bad habits leading to health issues. But while the direction of travel for tracking looks clear, further research is needed to stand up the tech's preventative potential.

"There's an awareness amongst the clinical community that wearables are here to stay," Cummins suggests. "They're going to be useful down the line -- and it's a case of just how to integrate them into the current clinical pathways or adapt clinical pathways to use wearable data. So I think there will be a change coming in how they're used in clinical decision making. But at the moment, you wouldn't use them, by themselves, for that."

"Let's put it in an optimistic way," adds Imperial's Mandic. "It's good to have an awareness about the possibilities of good wearables -- and for the public to get used to that idea -- until we have a class of variables which are going to be 'bulletproof' and rock solid, including being granted clearances as medical devices."