"Mark J." writes:

On 8/19/2019 12:09 PM, Sir Ridesalot wrote:
I went for a 40 kilometers ride today and the ride involved a fair
bit of rolling hills. An interesting observation was that at the top
of the hills my heart rate was nearly 20 bpm LOWER that when I was
walking around my apartment or just standing around talking to
someone.

Anyone else experience similar drops in heart rate whilst exercising
compared to their normal heart rate?

Not exactly what you asked, and probably won't explain your
experience, at least not fully, but:

https://en.m.wikipedia.org/wiki/Skeletal-muscle_pump

My /perceived/ experience is that my heart rate continues to rise well
after I crest a climb, and indeed may jump upward right as I ease off
at the crest. This could all be me hallucinating; I've never followed
it really closely with the HRM.

If my perceptions are indeed correct, my best-guess explanation is
that while climbing, my leg muscles are doing a lot of blood-pumping.
When I coast at the crest, the "muscle-pump" shuts down and blood
pressure drops a bit, stimulating heart rate to rise.

Is that how the control loop works? Obviously heart rate doesn't *just*
depend on blood pressure, because pressure rises significantly during
exercise. I would have guessed that the heart is roughly a positive
displacement pump, and the heart rate is more or less proportional to
the amount of O2 and/or CO2 that need transporting. How your body
figures that out I don't know.

It seems possible that the pressure setpoint is somehow set by metabolic
requirements, do you know if that is the case?