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Polar’s M600 is one of the few wrist-based oHR devices that will ‘properly’ support HR when swimming.
By that I mean that there is a swimming mode AND the optical HR works in that mode. Other watches, such as the Garmin 235 (optical HR), have optical HR DISabled in swim mode. Of course it’s possible to choose a regular sport and go swimming and the device will record HR when swimming. HOWEVER there seems little point in testing that sort of thing as the manufacturer will say ‘It’s not supported’ if the readings are wrong.
Anyway, it got me excited so I went off to test the support-oHR Swimming mode. After an excellent result in a 90 minute threshold HR test when running I had high expectations.
To avoid looking a bit ‘strange’ in the pool, I relied on wearing a Garmin HRM-TRI chest strap and leaving an accompanying Garmin 920XT in my locker. The HRM-TRI cached the HR data from swimming and uploaded it to the 920XT at the end. OK I looked weird wearing a HR strap when swimming but at least I only had one watch on! 🙂
Whilst I WOULD say that chest straps are fundamentally accurate; I wouldn’t necessarily say the same when they are used underwater and designed to be used underwater, like the HRM-TRI. Don’t get me wrong, the HRM-TRI would DEFINATELY be in my top-10 tri products, it’s just that when pool swimming there are opportunities at the start of each length for the strap to be pushed off the chest and for an erroneous result to be recorded. The HRM-SWIM reduces that chance and I do have one but it really is not comfortable IMO. So HRM-TRI it was.
So I start off by assuming the HRM-TRI is probably somewhere near correct. But I got some very strange results from the Polar M600. First off I had to offset the data by one minute to match the curves. I don’t know why. The internal clocks were in sync 7 hours earlier.
Then, as you can see, the M600 is recording lower values than the HRM-TRI. The same low values WERE displayed in use as well.
So the M600 is wrong and notably under-records.
I don’t really know but here are my thoughts. My short set was a few easy lengths and then a fast effort (repeated x5). Not enough to get HRmax for swimming but enough to get it up notably higher and I was using paddles as well. At the end of the first hard effort I stopped. The next one I did a few more easy lengths then stopped. The next one I stopped. Next two easy at the end then stopped. Next I stopped. And then I had a few easy lengths to finish off.
With that in mind it looks a little like the HRs match up when I have stopped swimming (6 troughs) ????
So my theory is that when swimming the bloodflow is somehow restricted to the wrist area. I swim with a relatively straight arm recovery so maybe there is some centripetal force causing readings to falter? Just a thought.
The bottom line is that I won’t use the M600 to record HR whilst swimming. Maybe it’s better when you swim slower (I wasn’t going that fast) maybe it’s better with slower arm movements in breaststroke?? The M600 recorded swim-laps well enough but there is no stroke detection.
A final strange thing. When wet I find the M600’s touch screen is nicely responsive. HOWEVER when messing around at the end of the pool I noticed that when the M600 enters the water the screens change. That’s how sensitive it is 🙂 not the end of the world I suppose.