Spurious HRM reading or HR?
 

This one's been bugging me for a few days. I have guestimated my max hr at 182, based on the highest that I've seen it during a hard effort. This weekend, during a hard effort in the middle of fairly intense ride I glanced down expecting something like 170 and was shocked to see instead 190. It climbed up a bit to 194, understandable due to sheer shock and a little fear. After a brief moment it settled down to around 168. I definitely hadn't been at a 100% effort, not all that deep into the red zone even. Just a sort of half-assed sprint.

I wrote it off to a spurious reading. But it did react to my reaction, and lasted for a good 5 or 6 seconds, so maybe it was the heart after all racing for no good reason. Either can happen. I know that no one can say which with any authority, but how often do you see spurious readings like that on a hr monitor? What's your best guess of the odds that it was one way or the other?

Mine often reads really high in the first 10-20 minutes of a ride. My max is 190 but I often see readings of 205-250 or so during my warm up. It seems like once I get a good sweat going there's a better connection between my skin and the band and the anomalous readings go away.

I'd like to add that 12 BPM higher than your estimated max isn't much and may in fact be your true maximum. Have you tested your true max recently?

A hard effort isn't necessarily long enough or truly hard enough unless you're purposely doing a graduated stress test or something of the like.

How long did it take to go from 194 to 168?

Even if you were coasting at that point, dropping from true 194 to 168 should have taken full 30 seconds, maybe longer. If you were continuing pedaling, even lightly, it would take even longer. If the reading near-instantaneously crashed down 25 points, it's almost certainly a HRM glitch.

It was maybe 20 seconds, but I think it's unlikely to be a "true" max heart rate regardless - if not a glitch, it would be something else other than effort that spikes a heart rate. That's the possibility that mainly concerns me.

CAR, I was thinking something along those lines. I'd just done 2 miles MUP (slow!), another 2 miles fairly easy in traffic, 2 miles hard and another mile harder so I was warmed up pretty well, it was around 90 degrees or just under and I'd been sweating for 5-10 minutes but just building up a good sweat. if that gives a spurious high reading that could be it.

I've also seen some interesting heart rates (195-205) reported by the unit I've used for the past few years (zephyr bt), usually corresponding to hard efforts early in a ride.
I'm confident it's an issue with the monitor since I had the opportunity to peruse my holter monitor results that included about 5 hours of riding, which never showed higher than 178.

That sounds good, I think I'm going with "spurious readings" unless and until something independently indicates otherwise.