Good tips to ensure HR accuracy?

Same experience here, works well for me for running and cycling, but lags a little compared to strap. In most training scenarios it works fine for me. Running intervals / hills and cycling anything other than a steady state ride I use the HRM. I clean mine every day after training and wear it basically 24/7 with HR enabled always.

Similar for me.
I wear a strap on nearly all my runs as this works almost perfectly and I am used to straps anyway.
The odd run with this (or a 235) shows the OHR is generally not bad for steady runs.

When I have used the OHR then found it works better for me about one watch "width" more than normal up my arm and quite tight.

... 1. On rainy days, water will eventually get in, it seems to result is small spikes in the HR

This is very interesting!

I have noticed after swimming that I have had some inexplicably very high spikes in HR.

For example, earlier this week, while driving home from work, even about 3-4 hours aftermy earlier swim workout, for a few minutes my watch was reporting my HR in the high 150s and 160s, while my phone was reporting my HR in the 60s and 70s.


Garmin sent me a free Swim-HRM to do some tests to try and see what the problem might be. I received the Swim-HRM on Thursday and wore it to go swimming
(2 miles, 1 hour).

During my swim my heart rate was very constant around 130 over the whole hour except for a couple of intervals when I was sprinting and my HR peaked briefly at 151 (demoralizing a good swimmer in next lane) and 164 (all out, final sprint). Then my heart rate returned to 149 for a one minute cool down lap. The really interesting part is that after I got out of the pool and my watch started monitoring my heart rate, it was showing 170 before quickly going down to the 120s then 90s, but over the next 3 hours it was bouncing around a lot between the 70s, 80s, 90s, 100ish, and 3 hours later it inexplicably jumped up to 170 while I was sitting around watching TV then soon returned to the 60s. About an hour later, again while I was just sitting around watching TV, it briefly spiked up to 148, then soon returned to the 50s and then the 40s, which is my normal resting heart rate.


It had never occurred to me that water might be getting inside the watch. I presumed that the waterproof rating was based on keeping all water out of the internals. Is that not the case? Is it more like waterproofing the very internals somehow and allowing some water in? I was thinking maybe the unusual spikes might rather be related to the optical HRM algorithms allowing a greater range of random fluctuation in trying to figure out what's going on, especially after being completely unaware of the swimming activity over a couple of hours which then caused the watch to be 'surprised' at such a sudden spike when the optical HRM is turned back on. So the next time it sees a jump (eg, getting up to get a beer), the algorithm has a much greater range to test.

Soon Garmin will have more data to look at and try to figure this out. But in the meantime, I am very interested in this water observation of yours.

It had never occurred to me that water might be getting inside the watch.

I'm sure they just meant water getting between the HRM and skin, which can happen when you've got the watch on tight and it's raining or a sweaty run. I don't think water can get inside the watch, especially where the HRM lasers are.

I'm sure they just meant water getting between the HRM and skin, which can happen when you've got the watch on tight and it's raining or a sweaty run. I don't think water can get inside the watch, especially where the HRM lasers are.

Thanks, that makes more sense, but the problem remains. How does one explain wild spikes 3 or 4 hours after a swim? Do you like my algorithm hypothesis? Still gathering data for now.

What about if you are careful to dry your wrist and the watch after a swim? If you see patches of water several hours later then you might infer it has come from "inside".

I've been out in very heavy rain for over 30 mins several times and not noticed such spikes later on.

Anyway if water was inside the watch, I suspect the whole thing would have failed by now...

What about if you are careful to dry your wrist and the watch after a swim? If you see patches of water several hours later then you might infer it has come from "inside".

Yes, that is something I should watch for (no pun intended).

I've been out in very heavy rain for over 30 mins several times and not noticed such spikes later on.

Not as intense as swimming for 1 to 3 hours.

Anyway if water was inside the watch, I suspect the whole thing would have failed by now...

I would think so too. Hence my algorithm hypothesis.

When I have used the OHR then found it works better for me about one watch "width" more than normal up my arm and quite tight.

Hey Tim. You started a thread over on the 235 forum a while back on this with some pictures, with others posting their experience as well. I can't seem to find it. Can you add the link here? Might be useful for some.