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HR major increase with time during runs

Former Member over 9 years ago

Hello

I have an issue which might not be a Garmin 235 issue as such but perhaps more about optical sensors and me in general.

I am 38 yo, reasonably fit and I run twice a week for runs generally between 8 and 18km.

I have had 3 watches with HR optical wrist sensors now. I have started with a TomTom Cardio multisport last year and thought the watch optical sensor was at fault and sold it. Then I bought a Garmin 225 and had the same issue. And well as Garmin released the 235 just after I purchased the 225, I bought a 235 because I am a geek ;-). Anyway all three watches have been showing the same issue.

This problem is that when I run my watch’s optical HR readings always go up steadily with time. On a steady run my HR optical reading will start at a pretty normal number (between 130 to 150 bpm depending on pace). But I can never maintain it. If I maintain that intensity the HR reading will keep going up, all the way up to over 180 bpm sometimes at the end of the run. Of course it does not feel as if my heart is pumping more as the intensity is the same. I feel no different. Only the readings go up. Even if I slow down during my run, my HR does not really go down, it will keep climbing steadily with time. What is odd is that the increase is almost linear. This is not a cadence lock as the numbers are different to my cadence. Even when I do intervals my HR fluctuates up and down fine but the long term trend is still showing a steady increase on average.

Now I know that the HR does fluctuate a bit with time as the cardiovascular system must divert blood flow to the skin to enhance heat dissipation but certainly not to the level I experience (+30/50 bpm vs same intensity level at the beginning of the run).

Although I need to point out that I have always sweat a lot when I run because my body gets pretty hot. I mean I really sweat a lot during a run as I need to combat my body heat going up. Therefore I wondered if that is not the cause of this issue for me related to the optical sensor technology. I understand that wrist optical sensors monitor the flow of blood on the wrist but when the body temperature goes up the blood vessels leading to the skin capillaries dilate. Therefore I wondered whether excessive sweating and excessive body heat could not play up with optical readings and interpretation of the blood flow? Being dehydrated and with the blood vessel dilatation, my blood flow might be altered and as a result my readings from the optical sensor. That would explain the steady increase of the readings

I never had a watch with a chest strap therefore I cannot compare or test. I'd be happy to buy one if I can be sure that optical HR readings can be wrong in my case but I do not want to buy one if that is not the case. Especially as I bought optical sensors watches to avoid having a strap

What do you think? Does anybody know if excessive body heat and or excessive sweating can cause optical readings to go up with time as the body temperature goes up or as the body gets dehydrated?

Thank you.

2 random graphs to illustrate this.

https://connect.garmin.com/modern/activity/1000385114

https://connect.garmin.com/modern/activity/981645254

0 Former Member over 9 years ago

In my experience significant cardiac drift is more likely to happen when
(a) Start at a fairly hard pace and try and maintain it
(b) Run in a fairly warm environment

You might be right but these are not hard pace. Although heat factor is evident for me. But could that play up with optical readings and explain such a delta is indeed the question... ;-)

It looks like both apply here as you were on a treadmill and your training effect was the maximum 5.0.

What happens with your HR if say instead of 9 min/miles you try for 10 min/miles and run outdoors (if possible)?

By and large if I run "within myself" - say 90 secs/mile slower than marathon pace then on a fairly cool day my HR would not shift much at all throughout.
If however I did a threshold run I would expect it to rise a bit throughout.

The maximum effect is biaised here. Same as vo2max mentioned earlier. This effort 5.0 is completely off as the hrm reading are wrong and that pushing the effort calculation up. These are easy runs which should read effect 2/3.

Regarding your pace variation question it would not slow down much. Like any runner when I slow down I feel better but my hr reading from the watch will keep its linear increase. This is showing on one the graphs at the end of the 8k run I think.

Running outside show similar results but not with such a big delta as I feel less hot and sweat less.

I really think that as I get warm the wrist optical reading is not accurate for me because of the blood flow changes no longer showing correct HR correlation.

0 Former Member over 9 years ago

Yeah that is my point. This is a slow pace run and it feels like a slow pace run. The readings are completely off. They do not reflect my

My VO2 max estimated by Garmin is 47 but that has got no real meaning as this is based on these HRM readings which are false. So the vox max estimate is false as my watch thinks wrongly I am in the anaerobic zone very quickly even on recovery runs.

No sorry I did not say I ran 36k in 2 runs per week. You are right, I do a variety of runs which I adapt every week as I can only dedicate 2 day / week to runnning: long, short, slow, fast, interval, etc. These runs vary and range from 8k to 18k.

I know we're all different, but I have to believe getting your heart rate up to 180bpm involves a physically perceptible struggle no matter the person. And as such, there's either something wrong with your heart or your optical sensor is giving you false data. I think your best option is to go buy a heart rate strap and see if you can replicate the data. I use one and I personally prefer it. I think it's good to have and use both. For me, the only time I can get my pulse that high is when I am sprinting at maximum effort or running up a mountain.

BIG EDIT: I just looked at your Garmin data for the first time, didn't see the links the first time I read through. Your cadence is well over 180spm in one of your runs (approaching 190spm!) but you're moving at a 9:15 mile pace most of the time. Your turnover is incredibly high for your pace. Elite runners move at 190spm when they are going at a below 5 minute mile pace. That could be (probably is) the reason for your elevated heart rate... I mean, it may not be evident in your actual pace, but you're moving your legs like you're running from a bear!

0 gpb11 over 9 years ago

@dam.k - With the three watches you've had (TomTom, 225, 235) that've given your these numbers, when you stopped in the middle of a run and checked your pulse manually, what numbers did you get relative to the watch figures? Apologies if you'd mentioned that measurement, I've missed seeing you mention it.

Anyway, you seem pretty sure these three watches have been giving you erroneous readings. I suppose it's possible, but as far as I know there's nothing I've heard of about sweat or heat adversely affecting optical HRMs. Dehydration is one of the causes of cardiac drift/creep as previously discussed, but again it's clear you don't think that accounts for what you're seeing.

It appears you have three choices: (a) return the 235 and go buy some other watch to try yet again, (b) borrow or buy your own chest strap and see if it's giving similar numbers, or (c) just keep discussing it here without adding any new info. I personally vote you spend the $40 on the chest strap and then not only will you know for sure, but you'll have it for use when doing activities that wrist-based oHRMs just aren't good at (e.g. stuff that heavily stresses your wrist)

0 Former Member over 9 years ago

I personally vote you spend the $40 on the chest strap and then not only will you know for sure, but you'll have it for use when doing activities that wrist-based oHRMs just aren't good at (e.g. stuff that heavily stresses your wrist)

I vote for this - not that my vote matters :). This is clearly important to you and understandably so. More data never hurts and it's important to have confidence in the data being collected. It's worth solving this puzzle!

Hell, i have an old strap lying around that you can have if you live in Australia. Over the years i've tended to accumulate a lot of stuff like this that i never use now. Happy to send it to you.

0 Former Member over 9 years ago

Yeah thanks. I kinda know that a strap is the answer as I got the same pattern with 3 different optical watches. Just thought somebody might confirm my assumption or contradict me to save me from having to test that. I'll sure give it a go since we are not certain. Thks for the offer anyway but I am in London.

To answer somebody's question about the watch's data vs. my HR manually checked, to be honnest I do not remember the exact numbers for these sessions in particular but it is always a lot lower than the readings.

Anyway yesterday I did an interval session and mesured my heart rate manually at the end of it again.

https://connect.garmin.com/modern/activity/1021783896

Don't be fouled by the pace numbers on the graph as I just got the Garmin 235 and I am still calibrating it so treadmill distance is always off at the moment and as a result pace graphs are a bit all over the place.

- 2km warm up at 5'43m/km
- 5x intervals: 400m at 4'17m/km + 600m at 6'00m/km
- 1km cool down at 5'43m/km

So pretty challenging pace although not totally all-out. My HR readings never went above 173 bpm during the hard parts so well below some of the readings I get above 180 bpm at the end of all my longer slow runs. As you can see my HR trend keeps climbing upwards with time as for my slow runs. Although I felt awesome and really recovered well between intervals or at the end. At the end after I stopped my actual HR (manual pulse check) was 144 vs. a reading of 166 on the watch...