HRM Strap vs Watch Discrepancy

Jun 10, 21 11:23

Post #1 of 24 (1959 views)

I don't train exclusively by heart rate, but I do look at it, and I had a weird experience switching between my chest strap HRM and the heartrate monitor on my watch. I'm wondering if anyone else has experienced anything similar.

Chest Strap: Garmin HRM-Dual
Watch: Garmin Forerunner 735XT

I normally wear the chest strap when I'm biking, and the watch when I'm running. I kept the chest strap on the other day when I did a pretty hard 2-mile run off the bike. When I was done with the run, it asked me if I wanted to update my HR zones based on a new threshold, and I said yes. Here's the weird part: It moved the zones by WAY more than I expected...the cutoff for each zone moved by about 24 bpm. What used to be the ceiling of my zone 3 is now the ceiling of my zone 2.

The actual heartrate readings don't vary hugely between the two (although I've never had them both record the same activity to compare), it was just surprising to see the cutoffs for the zones change by so much.

Anyone else experience anything like that when switching between HRM devices?

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 11:46

Post #2 of 24 (1943 views)

My 935 reads approx 7-10 bpm higher than both chest straps I’ve used (viiiiva and tickr). From what I’ve read, it’s common for the watch to be inaccurate due to it being an optical sensor, so I go by the chest strap numbers, and mentally subtract to make adjustments if I’ve gone out with only the watch on.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 11:56

Post #3 of 24 (1930 views)

I have a 945 and the wrist and strap are dead on the same

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 12:33

Post #4 of 24 (1905 views)

For most the optical built in wrist hrm is way off once you start moving. Trust the strap not the watch.

Re: HRM Strap vs Watch Discrepancy [lightheir] [ In reply to ]

Jun 10, 21 15:19

Post #5 of 24 (1867 views)

I know the chest straps are supposed to be more accurate than the wrist sensors, but I was completely surprised by the amount that it changed my zone cutoffs.

I haven't had the chest strap for that long, so I used to use my watch for the bike too. Remembering the types of heart rates I used to get on the bike using the watch (e.g. during my commute), the chest strap is not giving me readings that are THAT different from what I would see on the watch (certainly not 24 bpm different!). Maybe the bike readings are similar because there's not much arm movement happening on the bike compared to running?

The other crazy thing is that it didn't seem to change my HR zones for bike activities. So a heartrate that would be zone 2 according to the new run zones is a zone 3 or 4 on the bike.

Last edited by: ntl_tri: Jun 10, 21 15:20

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 15:45

Post #6 of 24 (1853 views)

It's not surprising to hear that the difference you're observing is mainly on the run. Your hand is moving much more on the run and having a greater effect on the optical sensor signal. I have an apple watch (3rd gen) and the HR sensor is useless for running. Having said that, I got the Polar OH1+ optical sensor that sits on the upper arm and the read out seems to be more stable.

Re: HRM Strap vs Watch Discrepancy [beston] [ In reply to ]

Jun 10, 21 15:58

Post #7 of 24 (1842 views)

That's what I thought too, at first. That the difference was just due to the watch being less accurate, especially for running. And I will say the chest strap (for the few times I've used it for running) has way fewer spikes and weird jumps in its readings. But honestly, the actual HR readings between the two aren't that different.

Here is some data, for comparison:

For the 2-mile run I mentioned in the original post, my average HR (chest strap) was 162, with a max of 176.

For a 5K time trial I did a couple of months ago, my average HR (watch) was 159, with a max of 176.

I know it's not a perfect comparison, the distances are different, but the effort was comparable. Especially considering the 2-mile run was after an interval workout on the bike, and the 5K was a stand-alone run.

I just can't fathom where the 24 bpm shift in the HR zones came from. Maybe I should stop worrying about it and go for a run. :)

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 18:15

Post #8 of 24 (1815 views)

ntl_tri wrote:

That's what I thought too, at first. That the difference was just due to the watch being less accurate, especially for running. And I will say the chest strap (for the few times I've used it for running) has way fewer spikes and weird jumps in its readings. But honestly, the actual HR readings between the two aren't that different.

Here is some data, for comparison:

For the 2-mile run I mentioned in the original post, my average HR (chest strap) was 162, with a max of 176.

For a 5K time trial I did a couple of months ago, my average HR (watch) was 159, with a max of 176.

I know it's not a perfect comparison, the distances are different, but the effort was comparable. Especially considering the 2-mile run was after an interval workout on the bike, and the 5K was a stand-alone run.

I just can't fathom where the 24 bpm shift in the HR zones came from. Maybe I should stop worrying about it and go for a run. :)

It's not hard to explain. Your optical HRM is wayyy less accurate and precise than your chest strap for running (and also likely for cycling.)

The optical wrist works well for HR at rest, but is usually terrible for running. Just use the data from your HRM and you're done. There is literally no reason to even debate this as the accuracy and precision of the external HRM unquestionably superior.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 18:59

Post #9 of 24 (1796 views)

my personal opinion is the optical HR on watches is close to useless. between my garmin 935, 945 and also the wahoo rival that i tested for a short time, HR is all over the place while running. its a completely unreliable metric.

80/20 Endurance Ambassador

Re: HRM Strap vs Watch Discrepancy [lightheir] [ In reply to ]

Jun 10, 21 19:09

Post #10 of 24 (1790 views)

lightheir wrote:

For most the optical built in wrist hrm is way off once you start moving. Trust the strap not the watch.

Yeah I don't know anyone that relies on the their wrist HRM. It's a tool that needs to be very reliable otherwise it's useless if you're left guessing whether it's working or not.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 19:58

Post #11 of 24 (1779 views)

My HR vs effort is very consistent, the problem I've had with HRM's is they lose signal and read really high until I sweat a bit for a strap or straighten my wrist for my optical on my watch.

Even on the run my watch HR sensor has been spotty.

But...my new 945LTE optical has been great for the half dozen times I've used it now. Much better than my 945 or 935. It might just work for me or maybe I'm exaggerating but the data has been really good.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 20:09

Post #12 of 24 (1767 views)

If you want your optical HRM to work even close to reliably, tighten it substantially. Mine works best when it's at least one notch tighter than the first sign of discomfort. haha

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Re: HRM Strap vs Watch Discrepancy [jaretj] [ In reply to ]

Jun 10, 21 20:13

Post #13 of 24 (1761 views)

jaretj wrote:

My HR vs effort is very consistent, the problem I've had with HRM's is they lose signal and read really high until I sweat a bit for a strap or straighten my wrist for my optical on my watch.

if you read the instructions on all chest straps they all say to dampen the pads before strappin' up.

that said, i never do, and i never have had any problems. im gonna assume thats due to differences in morphology between people.

80/20 Endurance Ambassador

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 20:22

Post #14 of 24 (1758 views)

I haven't experienced the big shift in zones that you describe, but since the strap/watch readings seem fairly close you may be dealing with correlation, not causation.

As evidenced from the replies, experiences vary widely with optical HRMs (especially when mounted near a flex area like the wrist). IME the optical on my Fenix5 is typically within 1bpm of my strap (I've done several runs and rides wearing both), YMMV.

ECMGN Therapy Silicon Valley:
Depression, Neurocognitive problems, Dementias (Testing and Evaluation), Trauma and PTSD, Traumatic Brain Injury (TBI)

Re: HRM Strap vs Watch Discrepancy [damon.lebeouf] [ In reply to ]

Jun 10, 21 20:24

Post #15 of 24 (1754 views)

I do, it gets better...worse...seems kind of random. Works better when it's cleaner and my skin is not so dry, tried all straps but the hard strap seems to work the best of the straps.

Like the OP I mostly just kind of look at it, mostly afterwards.

Re: HRM Strap vs Watch Discrepancy [DrAlexHarrison] [ In reply to ]

Jun 10, 21 20:57

Post #16 of 24 (1745 views)

DrAlexHarrison wrote:

If you want your optical HRM to work even close to reliably, tighten it substantially. Mine works best when it's at least one notch tighter than the first sign of discomfort. haha

Definitely my experience too...I tighten it down a couple of notches before I run and it seems to work less bad.

Re: HRM Strap vs Watch Discrepancy [lightheir] [ In reply to ]

Jun 10, 21 21:06

Post #17 of 24 (1739 views)

lightheir wrote:

It's not hard to explain. Your optical HRM is wayyy less accurate and precise than your chest strap for running (and also likely for cycling.)

The optical wrist works well for HR at rest, but is usually terrible for running. Just use the data from your HRM and you're done. There is literally no reason to even debate this as the accuracy and precision of the external HRM unquestionably superior.

That's the accepted wisdom (and probably the scientifically tested wisdom too), but if I look back at some of my efforts recorded on my watch, then comparable efforts recorded on the chest strap, the differences in HR aren't huge. Anyway, I train more by perceived exertion than HR, so I'm not sweating a few bpm either way. It's just the 24 bpm change in the zones that caught my eye...everything shifted by a whole zone.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 10, 21 21:23

Post #18 of 24 (1732 views)

It's worth taking a look at the graph of HR, and when the peak of HR occurred. A classic issue with chest straps is an erroneously high reading at the start of a workout (especially in cool conditions) when the skin is dry and there is poor electrical contact between sensor pads and skin. This typically resolves itself 5-10 minutes into the workout as you begin sweating. A more gradual rise in HR over the duration of the run would suggest the chest strap is working correctly.

A lactate threshold is normally only detected with a chest strap - OHR from the watch will not give you LTHR. If this is your first run with a chest strap, then that may be significantly resetting your zones. Which zone method are you using? Also, as a rough guide, you can expect your LTHR to be around 89-92% of maxHR (although there are outliers). Although many people have very little idea of their true maxHR, and using 220 minus age is a poor predictor for any one individual.

Re: HRM Strap vs Watch Discrepancy [damon.lebeouf] [ In reply to ]

Jun 11, 21 6:27

Post #19 of 24 (1653 views)

damon.lebeouf wrote:

jaretj wrote:

My HR vs effort is very consistent, the problem I've had with HRM's is they lose signal and read really high until I sweat a bit for a strap or straighten my wrist for my optical on my watch.

im gonna assume thats due to differences in morphology between people.

That is the same thing with wrist optical sensors that you said are useless.

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 11, 21 8:36

Post #20 of 24 (1632 views)

As others have stated, a strap is always going to be more accurate. Optical/wrist HR is good for aggregate daily use, but for sport-specific I always wear a strap...and have for more than 10 years. It's just better data...there are so many factors around good optical HR data, such as skin type/color, how you wear it, etc. If you're looking for data quality, the strap will be the best choice.

- John
"Have courage, and be kind."

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 11, 21 10:01

Post #21 of 24 (1614 views)

I got tired of the straps wearing out. They should be rechargeable by now also. I haven't replaced mine recently.

My 935 wrist HRM works great for me. Part of my job is working on BP cuffs and HRM's. The 935 is darn accurate

WHEN...........

You strap the sucker down tight-ish
Wear it higher on you wrist, not the part that bends but behind the wrist bones.
Shave your nappy caveman wrist
Clean your watch after every workout

Maybe I'm just lucky/unique. I would love for my watch to adjust my HR zones though, if it meant I was getting fitter. Unfortunately Connect seems to think most of my workouts are unproductive. Ha! Forever in over trained mode.

Re: HRM Strap vs Watch Discrepancy [ScoutMac187] [ In reply to ]

Jun 11, 21 15:19

Post #22 of 24 (1578 views)

ScoutMac187 wrote:

I got tired of the straps wearing out. They should be rechargeable by now also. I haven't replaced mine recently.

My 935 wrist HRM works great for me. Part of my job is working on BP cuffs and HRM's. The 935 is darn accurate

Can you define "darn accurate", please? Because, "I wear it, and it seems about right...." doesn't cut it.

I've spent the last three weeks trying to tease out a discrepancy in my HR strap measurements from what I think it "should be". I've been running with two HR straps (and now a third) and multiple head units (Fenix6, 920xt, and an edge130), trying to determine if the differences are HR straps, head units, environmental, or well....ME. I'm uploading data daily for Garmin to analyze to try and decide which device (if any) is in error.

I'm and electrical and software engineer. I've been designing precision measurement systems for various industries (from vet-med to aerospace) since 1992. So, I have some skill in error analysis and general measurement system troubleshooting. So, I find it somewhat entertaining when someone claims that their device is "darned accurate", if they have no established basis of "truth".

Re: HRM Strap vs Watch Discrepancy [ntl_tri] [ In reply to ]

Jun 12, 21 1:29

Post #23 of 24 (1526 views)

On a few occasions I’ve gone on a ride without my HRM strap, but using my Garmin 530. I almost always get an email from training peaks saying that a new threshold HR has been detected, and do I wish to update my zones. The new threshold is usually around 250bpm. Sometimes technology does weird shit. Forget about it and keep using the strap!

Re: HRM Strap vs Watch Discrepancy [Tom_hampton] [ In reply to ]

Jun 14, 21 11:41

Post #24 of 24 (1418 views)

Strap and wrist HRM and $18,000 heart rate and blood pressure medical device certified accurate annually are all within +/- 1-2 beats per minute

Should I post my certifications and degrees? Maybe my GPA? I find it entertaining when people........oh nevermind. Why bother, its slowtwitch.

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