HRM Reliability?

Hi there.

One of my regular running routes includes some hill sprint reps, comprising 4 x c. 250 metre uphill sprints and a slow jog back down, then a 60 second recovery between reps. These reps come after a three mile easy run so my HR is already around 150bpm when I start the first rep.

Naturally, each rep gets harder and by the last of the four it feels like my lungs are exploding and I can feel my heart pounding. However, with each successive rep my wrist-based HRM measures a lower HR than the one before, with the first rep peaking at around 180 bpm, but the last peaking at only 145 bpm (i.e. lower than at the start of the first rep). This happens every time I do these sprints.

Is there a good explanation for this, or is it just that my HRM is not sufficiently reliable? If the latter, why is reliability only an issue on these anaerobic intervals?

Any ideas? Thanks.

Dave

0 Former Member over 7 years ago

I've also had very similar results. I purchased my Fenix 5 last week, and first time I did exercise was last night (Football). I created a custom app for this with usual data screens etc. When playing my heart rate was showing as around 70-80 BPM, when in fact it is around 120-140. I notices that when I stop for around 1 minute the BPM will start to increase to what seems to be a more accurate reading. I understand that there is a lot of movement when playing football and this could cause issues with the readings etc, but I never had the issue before with a Fitbit.

I also went to the gym this morning to do some 'Strength' training.. just usual chest workout, biceps, stomach. The HRM seemed to be inaccurate here too, and this was with very little wrist movement. Again, I noticed that when I rested between sets the BPM would increase to what seems to be more accurate. At one point it went down to 55 BPM when feeling my pulse it was nowhere near this. Disappointing really as this also affects the calories stat !

On a positive note, I do like the Strength app, it auto-detects the type of exercise you are doing. Not 100% accurate but still like it.

0 Mentox over 7 years ago

Hi DaveBurt, the reason it is showing as "unproductive" is because so far you have had low readings so your watch now thinks that you are performing worse. So give it some time and it will correct itself.

0 Former Member over 7 years ago

FYI: I've had a similar issue with my Fenix 5. With just the watch, it starts off really hot and then dials the HR down. In fact, sometimes my warm up heart rate is as fast as my peak heart rate while a running race while wearing HRM. This is a bug, and everyone else that gave you a explanation similar to when Steve Jobs said "your holding the iphone the wrong way" when Apple had the Antenna-gate, is wrong. Call the help phone number so you can get this documented.

0 Former Member over 7 years ago

Hi DaveBurt, the reason it is showing as "unproductive" is because so far you have had low readings so your watch now thinks that you are performing worse. So give it some time and it will correct itself.

and that is the crucial thing. I'm not an elite athlete and enjoy the 'guidance' that the watch provides. However, after 3 days of hard exercise, because the HRM is inaccurate, I'm being told by the watch that I'm unproductive. If it is so bad then surely for the price, Garmin should include the chest strap. Personally I think for the features advertised, it's pretty crap when it doesn't work on the basics. P.s. the HRM appears to have NOTHING to do with the tightness of the strap and more to do with arm movement (I.e. the opposite of what I would expect and the more the arm movement, the greater the accuracy)

0 Former Member over 7 years ago

I'll provide another example. Today I was doing a weights circuit. 1 min exercise with 30 sec rest between sets. At the end of around set # 20, I checked my HRM and it said I had a heart rate of 50BPM. I'm definitely not that fit and my heart was thumping. I had the strap as tight as it could go without cutting off circulation. Is there a fix for this problem or should I be contacting Garmin for a replacement?

0 Igor over 7 years ago

GEde, I have the same issue. HR is nice for running, living, sleeping but not for strength straining, weight lifting. Big disappointment.

0 carl.andersson over 7 years ago

I'll provide another example. Today I was doing a weights circuit. 1 min exercise with 30 sec rest between sets. At the end of around set # 20, I checked my HRM and it said I had a heart rate of 50BPM. I'm definitely not that fit and my heart was thumping. I had the strap as tight as it could go without cutting off circulation. Is there a fix for this problem or should I be contacting Garmin for a replacement?

GEde there isn't a single wrist based optical HRM that would give you accurate results doing a weight circut, a crossfit WOD or any HIIT workouts.
This is because the OHRM measures blood flow to get a HR reading, and doing anything that involves flexing your wrists will introduce too much noise to get an accurate reading - especially in cases where your heart rate is spiking then recovering.
The only "fix" to that problem is to use a chest strap, if heart rate information is so important to you for these types of workouts.

I'm not sure why this comes as such a big surprise to so many people. A quick search on google would reveal this is a common problem that's been prevalent since the first OHRM devices and hasn't improved since. It's also unlikely to get better either because of the physical limitations of reading your HR information from the wrist.