Have you confirmed the HR meter is sending good data? Id say stop 5 minutes in and manually check your pulse. This happens to me all the time, but only in the winter.

Static electricity this time of year due to low humidity. A simple search would have provided probably a hundred threads exactly like this one

Very likely your initial readings are not accurate. It takes some moisture for the heart rate monitor to operate properly.

I see this all the time. I'll go out for a long run and my HR is all over the place, up over 200 even while I'm essentially jogging. Then, at the flip of a switch it drops to where it really is in the low 130's. Usually takes a few minutes until I break a sweat.

Try running your HRM under water to wet it before putting it on. That works for me.

I can feel this happen in all three disciplines. It's most pronounced for me swimming.

This is how my body works too. Or it's how my equipment reads it. Honestly I have learned to just kind of ignore it for the first mile or so.

I know nothing about any science behind it.

I experience the same thing. Warm up and a few leg stretchers and I'm gasping, then once settled I'm fine.
I now do a quick 2min warmup and let it settle before any runs to get the cogs whirring.

I experience this also... I'm thinking the initial oxygen debt might be a good (at least partial) explanation.

But, I'm wondering if stress response could be a cause too?
My heart rate seems to rise a bit with the anticipation of a workout... more so on race day. As I get into training, or the race, and relax my heart rate settles.

That is definitely not the reason. Oxygen debt does not have that effect. That is not how it works with HR. This is probably a heart rate monitor issue.

---

Simplify, Train, Live

Increased heart rate is not associated with "oxygen debt"?

Found this, and others, when searching oxygen debt via Google... Breathing rate and heart rate are elevated (to remove CO2) and this needs more oxygen.

Not saying you're wrong, just asking for more info...

How high ? Does it look "normal" albeit high ?

I'd think it's a poor signal off your hrm belt - not reading until you've worked up a sweat

Yes but this does not pertain to the original post at all. What you describe would result in a higher than expected heart rate AFTER a hard effort. For example, let's say that I am walking at a slow pace and my heart rate steadies out at 80 bpm. Now I go and run a hard 1/2 mile interval and my heart rate gets up to 160 bpm. As soon as I stop running, I start walking at a slow pace again. My heart rate will not immediately go back down to 80 bpm. It is going to take some time. This is partially due to "oxygen debt."

During the initial stages of a warm up you have the opposite effect. Your heart rate is TOO LOW for a given effort because it takes a bit of time to ramp up. During this period of time when heart rate is ramping up to where it should be, you are developing an "oxygen debt".

---

Simplify, Train, Live