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Minimum Heart Rate and Resting Heart Rate

There had been some discussion regarding MHR and RHR as reported by the 935.

First of all I must say that my understanding of RHR is that it is your lowest HR while you are awake. So when you look at the 4 hour graph on the watch first thing in the morning you might well see a MHR below the reported RHR.

To understand what is happening I knocked up a ConnectIQ app (technically a datafield) over the weekend to record my minimum HR over a period of time. I have uploaded the app the the app store and it can be found here: https://apps.garmin.com/en-US/apps/9d91352b-32b9-410a-b5b4-52bb60eafdd7

My datafield displays the lowest 6 heart rates observed during an activity and tracks the time at each of those. I put it into one of the data screens of an 'indoor' activity (cycling in my case as I don't want to affect my running statistics) and allowed it to run over night. This had the following result:

So during the time I was asleep my HR went as low as 44, albeit for two seconds only. Looking at the 4 hour graph on the watch gave this picture:

The recorded lowest HR here is 49, 5 BPM higher than the MHR I recorded overnight. Because I checked the datafield when I briefly woke up two hours or so before getting up and the minimum at that time was higher than 44 I know for a fact that my lowest HR of 44 happened during the 4 hour period displayed on the graph.

After I woke up, but before I got out of bed, I took a screenshot of the datafield (as shown above) and restarted the activity for a few minutes. The results was this:

You can now see a minimum HR of 51 while I was awake but before I actually got out of bed and done anything substantial. This I would say is my RHR according to the definitions I have seen.

Now compare that to the 7 day RHR graph:

Garmin reckons my RHR this morning was 51, which exactly matches the lowest HR I recorded while I was awake but completely 'at rest'.

So there you have it. I do not know how Garmin does it (sleep detection is done server side, not by the watch. My 935 doesn't 'know' when I am awake). Maybe the RHR is determined server side as well and transferred back to the watch?

Anyway, if you fancy having a play with this yourself download the datafield and see what you think.

Regards

Gerard

Ps: Having an activity running overnight does seem to affect the way sleep is recorded. According to Garmin all my sleep last night was deep sleep, which is unlikely.

0 chimpware over 8 years ago

Is the time tracked continuous at that rate, or cumulative? According to Garmin they are tracking the lowest HR you maintain for a minute consecutively if tracked over night.

0 CloggyAbroad over 8 years ago

It's cumulative at each individual HR at the moment. I'll see if I can add a "longest time at or below" at each HR.

0 kalamarios over 8 years ago

It's cumulative at each individual HR at the moment. I'll see if I can add a "longest time at or below" at each HR.

CHIMPWARE has a good point. Let us know what you find with continuous (not cumulative) intervals.

0 CloggyAbroad over 8 years ago

CHIMPWARE has a good point. Let us know what you find with continuous (not cumulative) intervals.

It's kind of done. At the bottom of the screen it now displays the HR at or below you stayed for at least one full minute.

So even though my (reported) heart rate dropped down to as low as 40 during the 7 hour interval or so that this recording was running the lowest that was obtained for a full minute was 50. This might mean 59 seconds at 49 and below and just one second at 50 but I don't know that.

The reason I haven't updated this thread this week is because I got this RHR graph over the last few days:

My RHR is actually in the low fifties. I can believe it goes up to 55 as an indication of over-training or illness, but I do not believe it can just drop down to 42 or so. I wonder if having an activity running while you're sleeping somehow affects the RHR calculation on the watch. Or maybe I did not have the strap tight enough. Or maybe the RHR algorithm just makes up random numbers?

0 Former Member over 8 years ago

Very nice analysis! And another reason i love the connect iq platform so much. If you know how to code, it's pretty easy to bang up a simple app.

0 timgrose over 8 years ago

Interesting analysis.

Looking at how much my 7 day "RHR" chart varies (and way more than when I merely used to note my lowest HR on waking with a HR strap) then I do find it hard to "believe" it and find make any actionable decisions based on it.

I see you got as low as 40 but even that night the "RHR" was 51. That is a huge difference. Was the 40 false? It might appear so. I guess, as I said, you can better analyse this if was also wearing a HR strap.

I guess if you wanted to take this further you could wear 2 watches overnight - the 935 just on "normal" OHR and then wear a HR strap and record a "run" overnight on every second recording and see how they compare. Or, I recall, there is a data field that allows you to see both but not sure if records both.

Also this min HR data field would also be useful if you could a variant for max HR. There is also an auto detection of max HR and sometimes this has "worked" and other times not. It has also falsely changed when I used a HR strap (a TICKR X as my Garmin one had a flat battery) but unfortunately disproved the Wahoo one is "better" as it had periods of clearly false high HR.

0 Former Member over 8 years ago

Looking at how much my 7 day "RHR" chart varies (and way more than when I merely used to note my lowest HR on waking with a HR strap) then I do find it hard to "believe" it and find make any actionable decisions based on it.

Tim, i wrote an app for the 735XT that uses the OHR to record the lowest HR value across a minute (can change to between 5 sec and 5 minutes). I put it in the first position in "Apps" on the watch, and when i wake up all i have to do is press start 3 times to open it. I wait for a buzz which tells me the watch OHR is activated and locked on my HR, then i hit start again. One more buzz tells me the timer is done and it has a lowest value. I never even have to open my eyes.

The app records up to 32 measurements and plots a nice graph. I take one every morning upon waking. I find this is an easy way to track my "just woken" HR and see how it changes with time. I agree that it's much more stable than the RHR value the watch calculated across each day.

You can find the app here: https://apps.garmin.com/en-US/apps/822d7f34-33d7-438c-8d03-01cd1affbb75

There's some "PRO" features which are kind of minor. If anyone wants an unlock code let me know.

0 R_Tellis over 8 years ago

Great app! I just loaded it on my 235. I've been using a similar one for ages but it didn't alert you to when the sensor had locked on so it's a PITA to have to keep checking before hitting start.

While the app I have been using does create a log of about 50 it is only viewable as a table on a different page. I like the graph on the main screen.

0 chimpware over 8 years ago

Tim, i wrote an app for the 735XT that uses the OHR to record the lowest HR value across a minute (can change to between 5 sec and 5 minutes). I put it in the first position in "Apps" on the watch, and when i wake up all i have to do is press start 3 times to open it. I wait for a buzz which tells me the watch OHR is activated and locked on my HR, then i hit start again. One more buzz tells me the timer is done and it has a lowest value. I never even have to open my eyes.

The app records up to 32 measurements and plots a nice graph. I take one every morning upon waking. I find this is an easy way to track my "just woken" HR and see how it changes with time. I agree that it's much more stable than the RHR value the watch calculated across each day.

You can find the app here: https://apps.garmin.com/en-US/apps/822d7f34-33d7-438c-8d03-01cd1affbb75

There's some "PRO" features which are kind of minor. If anyone wants an unlock code let me know.

Looks like a cool App, but when I went to download it it says not compatible with the 935 :p

0 Former Member over 8 years ago

Looks like a cool App, but when I went to download it it says not compatible with the 935 :p

Yeah sorry. I wrote this many months ago and have been using it for myself. I've decided to put it (and a few others) in the store and will wait just a bit to see how they go in the wild before i reformat them for the new watches. I don't have a F5 or 935 unfortunately.

So i'll get to it, but not for a few weeks perhaps.