Which heart rate monitor for ME/CFS?

heart-rate-1375324_1920There’s a very interesting discussion about wearable heart rate monitors on Science for ME. I’m not going to reproduce those discussions here but you might want to check them out. It’s free to become a member and it’s a very good forum.

There’s some research which suggests post exertion malaise (the cardinal symptom of ME) occurs, or worsens, in response to exercise and that it may be lessened or avoided by maintaining a lower heart rate. This may explain, at least in part, why people with ME cannot tolerate exercise. Exercise, including graded exercise therapy (GET) is the most dangerous thing a person with ME/CFS can do. So theoretically, by keeping your heart rate down to around 50-60% of maximum you have less symptoms. Or to put it a better way, you can avoid an increase in symptoms. This may still be difficult, or in fact impossible, for some sufferers as their resting heart rate is already close to that 50-60% range and very minor activity, something simple like standing up may push the person over it, but for some it may be possible.

If you do have a little leeway then you may even be able to safely carry out very light exercise (such as stretching, or light resistance training) without inducing a crash if you can keep your heart rate below 50-60% of maximum. I’m not sure there’s enough scientific evidence for that, so tread carefully, but it might be worth exploring, with the caveat that you cannot exercise your way better from ME/CFS. All you might be able to achieve is a small increase in fitness without a worsening of your ME/CFS. Maybe.

A rough calculation of maximum heart rate is 220 minus your age. Multiply that result by 0.60 (60% of your maximum heart rate) and try to stick below that, or 0.50 (50% of your maximum heart rate) may be better but harder to achieve. Each individual is different and it’ll probably require some trial and error.

I have been meaning to get a heart rate monitor for a while but was overwhelmed when I first began looking. There are lots of devices on the market nowadays. The market is largely fitness orientated but it is still finding its feet and some devices are more niche  than others. I think the market still has some maturing to do, bugs to iron out both in terms of hardware and software and that means you need to exercise caution when buying a device because chances are a lot of them will have major design and manufacturing faults, particularly in the lower price brackets.

From what I can see the main thing to avoid are fundamental product killers like irreplaceable rubber straps which are known to snap, meaning the product goes in the bin a few months after you buy it. And you want to be careful not to pick a heart rate monitor that is totally inaccurate too. Although heart rate monitors are very common on these devices I think this is where most technological improvement is still required and there are certainly some limitations to be aware of which I’ll touch upon.

I’ve looked at what devices are reviewed if they look suitable or not. That’s a bit further down in this article but first I started by listing my must-have features. Your list may vary to mine. In terms of budget I’m looking roughly in the range of £80-£120. That rules out all the true smart watches such as the Apple Watch which are more expensive, instead I’m looking really at fitness trackers, some of which are bands and some are more watch-like. Most will provide notifications from your mobile phone for example, but will not allow you to respond via the device. Some do have native GPS in the watch while others require you to have your phone with you in order to use that functionality. This isn’t actually an issue for me either way as I won’t be using GPS to log where I’ve been on my runs because running – walking even – is totally out of the question for me.

Essential features:

  • Decent heart rate monitoring
  • Ability to set heart rate threshold alerts (beep, vibrate, or both)
  • Heart rate recording over time with data I can access
  • Real-time continuous heart rate monitoring with good update frequency
  • Waterproof (I don’t want to have to take it off when I have a shower)

Nice-to-have features:

  • Decent sleep tracking
  • Bedtime alerts (to encourage me to get to bed earlier)
  • Decent battery (I don’t need this as I don’t get out much, but come on, who wants to have to plug it in every day?)
  • SP02 (I’d like to know my oxygen saturation because I get breathless and it’s a useful measurement for sleep monitoring)
  • Gentle wake up alarm in light sleep
  • Recurring alarms (I have to take medication each day, I often forget and this might help)
  • Activity tracking (I don’t do much but it might be useful to know how small activities impact me)
  • My preference is for a watch rather than a band/bangle and a changeable strap rather than a rubber one.
  • Apps – with some devices you can load third party apps onto them, which make use of the sensors and data they collect to do bespoke stuff that the watch doesn’t do out of the box. I don’t know how useful this will be in practice but in theory someone with the right skills might code an app or two that provides functionality useful specifically for people with ME/CFS.
  • Heart rate rhythm/variability – I doubt think this is likely to be available via a wrist-based device though, so I’m not expecting to get this.

As an aside: most wearable need to be paired with your smartphone and/or computer so that you can easily set things and view data. Most of the time you can do this, or some of this, using just your watch but it’s easier on device with a larger screen. Compatibility with smartphones tends to be good for most devices but if you buy one you might want to check first that it’s compatible with the phone or computer OS you use.

Things I don’t need:

  • GPS
  • Exercise tracking and goals
  • Notifications from your mobile phone

Focusing on the features I do want, here is a bit more detail on how they work and why I want them:

Heart rate monitoring and threshold alerts

There are two main forms of heart rate monitoring: electrocardiography (ECG) and photoplethysmography (PPG). ECG is what is used in a hospital setting and that’s because it’s accurate. ECG directly measures the electrical signals from your heart. You can buy devices with chest straps to measure your heart directly and they are very accurate, but it’s not convenient and a lot of people with ME struggle to breath enough already without a strap around their chest to make it even harder. PPG is less accurate than ECG, using a light to sense subtle changes in blood flow. PPG can be used on your arm which is why all wrist-based wearables we’re looking at use this technology. Essentially this means it’s very important that the algorithm that interprets the PPG signal is good so that it accurately calculates your heart rate. There may also be some hardware considerations, as the sensor needs to be able to touch your skin and block out ambient light to get a good reading. Some devices manage these things better than others. The good news is that the main drawback of PPG is in measuring accurately when people move around a lot, meaning the technology can struggle to perform when people exercise but the technology should cope just fine with me lying in bed or sat on my sofa.

If you can measure your heart rate then you can avoid too high a heart rate and going into your anaerobic threshold. You don’t want to have to watch your watch all day long for when your heart rate gets too high, what you want is a device which can alert you if you go over that specified threshold. I’m hoping I may have capacity to try some very light and careful exercise, maybe just stretching; after a decade of inactivity I am very unfit, my weight’s likely to become a problem. I won’t be able to get fit, but if I can improve my fitness even a little that might put off development of other health problems.

Real-time continuous heart rate monitoring with good update frequency

This is important. Not all fitness trackers measure your heart rate 24/7. And even those who do may not do it quite how you expect. What many trackers do is they regularly take your heart rate, say once every ten minutes, and they do this because it saves on battery power which you’ll understand is a limiting factor on these small wrist-worn devices. The problem is this won’t meet my needs. I want to know in real-time if I am heading into anaerobic territory, not after it is too late. Some trackers also give averages rather than true readings, so they sample continuously but every 30 seconds work out an average and report that. That also isn’t what I want.

Sleep tracking

Typically wearable devices guess at this quite a bit. They tend to assume you are asleep if you have not moved your arm for about 1 hour. I think this is a bit rubbish. Some devices also look at your heart rate to help work it out, or you specifically tell the device when you are going to go to sleep.

Most also do not cover daytime naps. One or two do. I tend not to nap in the daytime so this isn’t a problem for me, but it’s something to be aware of if you are a napper, which I know a lot of people with ME are.

In terms of what they are measuring, some measure heart rate, but most measure movement, and some measure breathing (I guess through recording noise via a microphone?), and some (but none of the ones I review below) also measure ambient temperature, which I figure might be useful but it’s not that commonly tracked by most devices.

What I’d really like from a tracker is something to tell me to go to bed! I struggle so much with getting to bed early – or rather, not late. I think because my brain functions a little better late in the day, which I suspect may be due to higher blood flow (we’ll see) and because once I lay down for sleep I have no distraction from my symptoms, they flood into my consciousness and I hate it. Still, a prompt to go to bed half an hour earlier than last night in order to optimize my sleep based on sleep data recording would be very welcome.

Finally, some devices can gently wake you up when they think you are in a light phase of sleep within a specified period of time. That might be handy, I’m not sure. At the moment I wake up eventually and then typically dose until I have enough energy to roll out of bed. But I’d be interested in trying this, maybe it would help.


SPO2 is a measure of oxygen saturation in the blood. I’ll tell you now that none of the devices I review below provide this feature, which surprised me – I know SPO2 monitors traditionally have a cord and device which you attach on your finger but I thought some watches may have this as a plug-in accessory. Or that maybe someone had figured out a way to measure this on the wrist rather than the finger (is that really beyond the capabilities of man?). I have a simple and cheap SPO2 finger monitor which I wore a few times at night in the past and I found that my oxygen level drops sometimes for a short number of seconds (into the 80%s, which is bad). I’m pretty sure this was accurate too because my heart rate (also measured by the device) would increase to try and compensate at the same time. But the device is not the sort of thing you can wear comfortably all the time. I’d like it on a wrist-based device (which would have to have true second by second recording otherwise it would miss it). Oh well, maybe in the future.

VO2 Max

Those who are familiar with ME/CFS research will know about the two day cardiopulmonary exercise testing (CPET) studies suggesting that those with ME cannot perform to the same level as the healthy subjects. Part of this test involves VO2 max. Some wearables are able to estimate this. Basically they have you exercise at a maximal rate (usually measured by ensuring the wearer is exercising within a certain heart rate rate zone that the wearable is measuring) for a certain period of time and distance (typically measured by the wearable using GPS to track distance). I wouldn’t use this – I wouldn’t be able to as I cannot exercise at anything like the rate required – but I’d be intrigued by this measure if I was only mildly affected as I could potentially carry out my own version of a 2 day test of my own to see PEM in action.

Ruling devices out with fundamental problems

There are a lot of different wearables out there, all a little different. I found it pretty overwhelming at first and had to work through the options which took me some time. I started by ruling out the devices with fundamental issues.

I don’t trust positive reviews you find on the internet, and maybe not all negative reviews either, but the negative reviews often do tell you if a product like this has known issues if they come up over and over again. What I discovered is that many wearables are plagued by poor design and cheap quality parts – watch straps often are made of rubber and snap, and if the strap cannot be replaced this means a fault like this kills your device.

This ruled the following devices out:

Fitbit Alta HR – as above, basically the same problems. What’s the point in a device if the strap breaks? Also reports that the screen scratches easily and cracks. Specific reports of sleep tracking being rubbish.

Jawbone Up3 – the company has gone/is going under from what I heard, which is why you can pick these up so cheap, but as with the Fitbit a lot of these rubber strap designed products just don’t last and it sounds like you’ll be lucky to get 6 months use out of it before the strap snaps and you have no choice but to pop the whole thing in the bin.

Garmin Viviosmart 3 – another with rubber straps that break and can’t be replaced. Looked quite good apart from that, but the device’s other features cannot rescue it from the major design flaw in how the thing attaches to your body.

Garmin Viviosmart HR+GPS – Straps which according to some reviews cause skin rashes/reactions. Not much better than a snapping strap really. Complaints of inaccuracies in activity tracking and bad GPS. Oh, and Bluetooth connectivity problems.

These might work for some and might be very good, but I want to avoid the hassle when they break and you have to try and get it fixed/replaced/refunded.

The finalists

Moving on, the remaining devices may have some common faults which I will highlight but nothing that fundamentally means I should avoid buying them full stop. Hopefully not anyway. Target prices below are based on the lowest price the device has been on sale at recently from Amazon.co.uk

Huawei Band 2 Pro – target price ~£50

s6-huawei-band2-2The Fitbit Alta HR didn’t make it this far, but if you like the look of the Fitbit device then you’re in luck because this band from Huawei looks very similar indeed, another sleek, minimalist device. Only, the Huawei device doesn’t snap. It’s well put together, and the touch screen is responsive. Reviews praise it for its accuracy of activity tracking (step counters etc) and although I won’t really be using those features much it suggest Huawei know what they’re doing because it’s hard to get right – or at least the majority of manufacturers appear to get this hopelessly wrong. While other devices add thousands of fake steps while tracking this device seems to get it right almost all the time. Another thing I won’t use much on account of not getting out much is the GPS but reports are that it is very good compared to the competition.

The strap seems reliable enough although it is a mix of silicone and plastic and doesn’t appear to be changeable. It also has a somewhat insecure fixing method where button fasteners pop into place and if you catch the strap on something it can un-pop accidentally. May not be much of a problem for me but for those more active it may not be ideal. It’s waterproof to 5ATM. As an added bonus it has a breathing coach, where you can complete breathing exercises and it scores you on how well you stay focused. I’m dreadful at meditation/breathing type stuff but maybe this will be valuable, to be honest even a breathing exercise is a physical workout for me, so maybe it would be a place to start in my case.

Heart rate tracking, heart rate limit alert, sleep tracking which includes analysis of your heart rate to assess the quality of your breathing, supports daytime naps too, native GPS, VO2 Max…This is a really good list of features and add to that up to 21 days battery life and this is starting to look like an impressive device for the money. The retail price of this device since it launched in the UK in September 2017 is £80 and that seems quite reasonable for what you get, but it’s been at around £50 at Amazon recently, which seems an absolute bargain. I think the main reason for this is because Huawei, although they are a massive company are not well known in the UK, they area a Chinese company and they have to overcome that brand problem where everyone follows the crowd and buys the familiar brands even if they aren’t as good.

The one area where the Huawei does fall behind the competition in real terms is the app — although it has everything promised, and isn’t in any way bad – it still isn’t as refined as most of the competition. I don’t mind this too much though, as long as the data is there, I’ll get used to how to access it. There aren’t that many complaints of fundamental faults that seem to plague the competition. My only gripe is that I wish it was more watch-like than band like, but you can’t have it all.

Fitbit Charge 2 HR –target price ~£90

charge2-black-silver-tpu-regular-0-89079973ccd38c8059a0a68eb21fc858I originally had this item ruled out as there are reports of significant inaccuracies in tracking (mainly activity tracking with isn’t much of an issue for me anyway) but more worryingly there are lots of reports of the straps snapping/falling apart, and I thought the device did not have changeable straps. Turns out I was wrong about that as pointed out to me by a reader – thank you “zzz”.

You can change the straps and there’s a good selection at a reasonable price.

The device is quite comparable to the Huawei Band 2 Pro in terms of features. It doesn’t have native GPS but that was never a big deal for me anyway. Although the screen is similarly small to the Huawei the Fitbit gives you the option to customize the clock face a little, which is nice. It also tracks sleep and looks almost as good in that respect.

From what I can see it claims to measure HR about every 5 seconds in standard operation, though there is some good info to suggest it’s really achieving something more akin to every 10 seconds in practice. Still, that is a lot better than Huawei Band 2 Pro, which I can’t find official data on but I am collecting data on and will post about once I’ve figured it out a bit more (it’s nowhere near as frequent). Both bands are similar in that you can set an exercise mode and then it tracks every second.

The other advantage of Fitbit is that the app is more refined.

This looks a good device in my mind, there are only a few drawbacks to the Fitbit: There is no heart rate alert (this might become less of an issue for me in time once I learn my limits), it is not waterproof (it is described as splash proof but you can’t shower in it), and there is no integration with the Apple Health app.

A good device though which might suit a lot of readers.

Huawei Fit Smart watch – target price ~£115

fit-kv-watchIt’s the design that looks the most watch-like, and you can change the design of the watch face display. The materials used seem pretty good according to the blurb. Decent quality glass on the watch’s touchscreen so that it shouldn’t smash or scratch. Stainless surround which looks of good quality and a strap made of materials that have been tested not to cause allergy. The battery will last up to six days apparently. There are some reports of the rear glass which houses the heart rate sensor delaminating/cracking though, which is a concern. There are also some reports of connectivity problems with iPhones which is also a concern, though it’s possible later firmware updates have fixed this. These problems almost make me want to rule it out but it does come with a two year warranty in the UK (as does the Band 2 above) so that at least offers some protection should you run into problems.

The clock face on the watch is always on as opposed to most smart watches which is more convenient. Huawei seem to be able to afford this feature because the watch’s battery use seems to be quite efficient (though not as efficient as the Band above). Most other smart watches turn on when you rotate your wrist, which is acceptable, but on all the time would be better.

You can tell the watch to constantly monitor your heart and when you do this it displays data over the last four hours including curve, minimum and maximum, but not the current measure. I think this is rather odd and makes me suspicious they aren’t sure it’s terrible reliable as a real time monitor – because PPG technology can be inaccurate manufacturers prefer to use an average measure rather than a real-time measure. You can see the real time heart rate but only in the app, not on the watch itself (at least not in the continuous measure mode).

Like the Band 2 above you can easily set a maximum heart rate alert to ensure your heart rate doesn’t go too high and kick off PEM.

The watch is waterproof to 5ATM, and unlike a lot of other devices I haven’t read any stories of this waterproof claim being a myth – it looks like Huewai can be trusted on this. It’s promoted as suitable for swimming. I used to swim and would have loved – LOVED! – a watch like this back then, but although I can’t swim any longer it’s good that this will survive a shower (not hot!) or some accident that sees a glass of water pour over it.

This watch doesn’t have native GPS – that is the main thing is doesn’t have compared to the Band 2 from the same company. It can use your phone’s GPS instead which means if you go on a run you’ll need to take your phone with you to use this feature – not a problem for me as I rarely leave the house and haven’t run for 15 years.

Garmin Forerunner 35 – target price ~£105

sc-02-lgAttractive if a little bulky looking, this watch is designed primarily for the runner. It does everything necessary, and is waterproof to 5ATM. It has good battery life, lasting up to 9 days. It comes with a silicone strap but like the Huawei Fit Watch above you can change the strap if you want to, which is great. It has music controls for your phone, which is a nice feature if that’s what you’re after.

Quite a number reporting the heart rate monitor isn’t very inaccurate. That’s a bit of a concern although it’s always hard to judge these comments because these devices have to be fitted correctly in order to work, and there are lots of positive reviews also, but it’s potentially an issue. There are also a fair number of complaints about problems syncing the watch to your phone.

The heart rate is recorded every second in an exercise mode, but otherwise the measurement is variable, certainly not constant.

Garmin Vivoactive HR – target price ~£125

cf-lgFitted with a colour screen, it looks quite an attractive display. The battery lasts up to 8 days which seems pretty good. Like the other devices we’ve looked at it’s got the essential features and like the Garmin Forerunner it has changeable straps. That’s important because like with their Vivosmart offering there are complaints that the rubber strap causes them a rash. It is only because the strap is replaceable that this item made it this far in my review. The most concerning thing is that a fair number of people report that the screen can suddenly crack for seemingly no reason – the watch is sold with “chemically strengthened glass” so that’s particularly disappointing. And there’s also reports that it is not properly waterproof despite a 5ATM rating, which if true is a big problem in my eyes. I’d say this device was right up there but the faults might kill it, especially as it is one of the most expensive I’m looking at.

Like the Garmin Forerunner, heart rate is not measured constantly unless it’s in an exercise mode. It will periodically record your heart rate but it’s not clear how often.

Summing up

I’d have liked to have considered a Huewai Watch 2 but it was just a little too expensive for me. I’d also have liked to try a full-on smart watch like the Apple Watch, Garmin Fenix 5 or Samsung Gear Fit 2 but these were all more expensive and I just couldn’t justify it. If money is no object maybe check them out and see how they compare.

I went ahead and bought the best device, which is the Huawei Band 2 Pro. I didn’t buy it because it was the cheapest, that was just a happy coincidence (I’m not a cheapskate, honest!). The only thing it lacks is the ability to install third-party apps. I’ll report back how I get on.

Looking further ahead I hope the market matures, particularly with regard to getting rid of the fundamental flaws with straps that snap or cause skin reactions. Even though I’m looking at the lower end of the market those sorts of faults are still unacceptable. Hardware and software will improve, the same as how mobile phones matured a decade ago – you can’t afford to have hardware or software that doesn’t work, people will never buy from you again if their experience is poor. I don’t know who else will survive in the market as it matures, but it will be a difficult balancing act between keeping costs down and producing a high quality product and delivering more features – that’s what people want: lots of features that are relevant to them (but the fundamentals must be right first).

It’s an interesting market because it’s only going to grow. There is so much further technology can go with basics like sleep and heart rate tracking. And health tracking is the most interesting growth area in my opinion. Sure, anything to do with social media, fitness, information, and conveniences such as payment via your watch (already available on some devices) are going to sell but you compete with the mobile phone, with the laptop…wearables that tell us more about the body itself is the interesting area of the market. The FDA have shown an interest in this and sound like they are going to make it easier (and I guess cheaper) for companies to innovate and market their health-focused product. That’s absolutely necessary because otherwise the sorts of innovations that could be commonplace in ten or twenty years’ time won’t happen. I want to wear a watch that will inform me and the emergency services if it detects me having a heart attack, to measure glucose without needles if you have diabetes, to tell the wearer about their hormones, inflammation, medication even, that’s what I’m interested in seeing develop. For now though, I’m looking forward to taking a closer look at my heart and a few other basics.

Regardless of whether my experience with the Huawei Band 2 Pro is positive or negative I’ll write a blog post on how I get on and whether it proves helpful from an ME/CFS point of view.

edit: there are some comments from readers below and also some further comments/discussion of this article on a new Science for ME thread: https://www.s4me.info/index.php?threads/blog-clark-ellis-which-heart-rate-monitor-for-me-cfs.1567/