Why the discrepancy with my heart rate monitors?
April 2, 2016 12:22 PM   Subscribe

I usually wear a Wahoo TICKR heart rate monitor when I cycle. Recently, our office purchased us FitBit Charge HR wristbands as part of a "get healthy" initiative... They don't really seem to agree.

So, last night, I got on my bike (on a trainer in the basement - I use it with Zwift on my PC) and strapped on my Wahoo TICKR, which reports my heart rate to Zwift via ANT+. This is what I typically use.

I was recently given a FitBit Charge HR. Whatever. I don't know that I'm overly interested in it, but it was free, so why not. Out of idle curiosity, at various points throughout my ride, I checked my heart rate on the Charge HR, and was surprised to find that it was way, way different than my TICKR. As in, for a bulk of the ride it was 30 bpm lower than the TICKR.

I was working up a pretty good sweat and the TICKR was reporting I was right around 130 bpm, but my Charge said I was at about 96!

This is just one data point, but they never really at any point agreed. I think at some point they were within 5 bpm of each other, but, that was about it. I guess I could have stopped and actually measured my heart rate manually, but in the middle of my ride that didn't occur to me.

I wonder why they were so different. I wonder which one is more trust worthy! I wonder if anything I'm doing could contribute to one being more reliable than the other!

posted by kbanas to Sports, Hobbies, & Recreation (16 answers total)
It occurs to me that the Charge was low on battery. When I woke up this morning, it was dead. I wonder if a low battery charge can result in inaccurate heart rate recording?
posted by kbanas at 12:27 PM on April 2, 2016

Second hand but a coworker mentioned yesterday that his Fitbit HR is always about 40bps below his other HRM.

Further discussion suggested that monitoring via wrist isn't terribly accurate.
posted by Awfki at 12:45 PM on April 2, 2016

Well that's stupid.
posted by kbanas at 12:55 PM on April 2, 2016 [1 favorite]

Personally I find my Charge HR very accurate. I had heard anecdotal reports that it wouldn't register changing heart rates well, like during interval training, but I haven't found that to be the case for me. Consumer Reports tested the device and found it to be very accurate as long as it's worn as directed (a few inches above the wrist on the forearm, not down close to the hand like a watch).
posted by telegraph at 1:04 PM on April 2, 2016

The wristbands really are that bad and this phenomenon really is that dumb. Don't get me started on the HRM (or worse HRV!) app that use your phone's camera & flash.
posted by mce at 1:05 PM on April 2, 2016 [1 favorite]

I just tested my fitbit charge HR by actually counting my pulse, and the HR is reporting exactly the same number I counted, so at least currently it seems vey accurate.
posted by primethyme at 1:50 PM on April 2, 2016

My Fitbit and Garmin watch HRMs are both accurate on me. I have heard accuracy can vary from person to person? But that makes me think it's more an issue with someone wearing it incorrectly (wearing it too low on the wrist or too loose, for example).
posted by joan_holloway at 1:54 PM on April 2, 2016

But that makes me think it's more an issue with someone wearing it incorrectly (wearing it too low on the wrist or too loose, for example).


I confess to not reading the manual or anything - I just strapped the damn thing on my wrist - and, based on the descriptions in this thread, likely way too low (just like a watch, for example). So, I'll try wearing it a bit higher and also I guess I don't really care how accurate it is - I just more want to make sure there's not some kind of issue with my TICKR.

Thanks everyone!
posted by kbanas at 2:18 PM on April 2, 2016

I am in my 70s & started running about a year ago. I didn't much want to keel over dead, so I looked at heart monitoring:
1. On treadmill at gym.
2. Got a Polar around-the-chest & watch style monitor
3. Android app.
They vary a great amount, but in general stay within 5 of one another (except when they go into divide-by-two mode, or just go totally nuts, which they all seem to do sometimes)

I regulary exceed the 150 bpm my age says is 100% effort (eg-you will die) Top is about 180 (for a quarter mile at 7:30 minutes/mile pace)

So I also had a cardiac stress test (which indicated no problems at 160 bpm, when the test stopped), and talked to the doctor about it.
He, and I think the recent NY Times article, say:
The devices are all crap. Pay attention to how you feel!
(I interpret this as keep to at most 1 breath per two strides, and no dizzies)

Or, as Henny Youngman put it:
Patient: Doctor, it hurts when I do dat.
Doctor: Don't do dat!
posted by hexatron at 5:25 PM on April 2, 2016 [1 favorite]

You don't have two heart rate monitors there. You have a heart rate monitor, and also a FitBit.
posted by kindall at 5:32 PM on April 2, 2016 [2 favorites]

I thought fitbit was getting sued because their heart rate monitors were off.
posted by notned at 8:29 PM on April 2, 2016

Yup. Google confirms.
posted by notned at 8:32 PM on April 2, 2016

I thought fitbit was getting sued because their heart rate monitors were off.

Anyone can get sued for anything. That proves nothing.

Just compared mine to my pulse and its spot on. Its more accurate if you wear it higher up your arm - about an inch above your wrist bone. They're not perfect and not 100% accurate but if its out by as much as you say then their its faulty or you're wearing it wrong.
posted by missmagenta at 8:46 AM on April 3, 2016

I have a fitbit (Surge) which is worn according to manual. I have a problem which affects my heart rate, so I'm pretty interested in this feature. I compare the fitbit heart rate to the pulse/ox finger tester each visit to my doctor's office; sometimes the fitbit is accurate, sometimes it is not.

Each time they're using the pulse/ox device, my heart rate has just shot upwards by 50+ bpm. I thought it might have difficulty keeping up with abrupt change, but sometimes it does manage. I don't know.
posted by galadriel at 5:42 PM on April 3, 2016

I had this problem. My Charge HR is accurate to my pulse when I'm stationary but the first time I used it working out I was dying on my rower and it either wouldn't give me a reading or it said 78 (LOLOLOLOL). I hopped on the google and the Charge HR should be worn higher up on your arm when you're exercising as it gets a better pulse reading, especially if you're bending your wrists to row, bike, etc.

Wear it higher on your arm (the width of 2 or 3 fingers up) and see what happens to the accuracy.
posted by good lorneing at 6:41 PM on April 3, 2016

DC Rainmaker reviews a bunch of fitness gadgets, and I've linked his review of the surge. He didn't find the device very accurate for actual exercise, but found it to look pretty good for daily activities. Given the work he puts into his reviews, I assume that he's wearing it correctly.

Additionally, the further away one's skin is from lilly-white the worse an opticial heart rate monitor will perform. I'm unsure if your skin colour might be part of an issue.

One of my co-workers got a chest monitor (also a wahoo tickr) for exercising since his heart surgery. He also got a surge because he found the chest strap uncomfortable. He said that when comparing them the often disagreed while he was exercising. At various large points of disagreements actually taking his pulse showed the surge to be off. He shortly returned it as he didn't need a heart rate monitor for when he's not exercising. He's fairly light skinned.

I'd assume the surge to be inaccurate, and consider the heart rate info only for entertainment purposes.

Battery also likely may have been an issue. Even with my wahoo tickr, I know that it's time to change the battery when it seems to be slower to change HR values based upon my perceived efforts.
posted by nobeagle at 7:20 AM on April 4, 2016

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