Dropping HR during a race (10k), what does that mean?

Happened to me two weeks ago when I ran a 10k in a middle of a training block. Aerobic system was fine but legs were heavy and couldn’t push.

do you drink a sh*t ton of alcohol?

lol, nope, I wish.

It's very common when the legs can't continue to deliver the effort to maintain the HR.

On something like 6x1000m, I'd notice on the last one that at a point, I'd hit close to max HR and it would then drop back a bit...

I should add that this is one reason that V02 max on a treadmill might not reflect true V02 max as the legs give out before the limits of oxygen capacity are reached.

How do you measure HR? Wouldn't rule out error if you don't use a strap. Did your pace fall off with the decrease? Sometimes you just don't have the legs. Usually HR follows pace when that happens.

That happened to me when I raced a HM a few months ago. Felt aerobically great but my legs turned to lead the last 4ish miles.

It was just the optical HR monitor on the watch. I can usually spot the bad data though, and like I said, it's either an abrupt increase or decrease. This was just a steady decline. The pace was very similar as the race went on, which is why it was so odd.

I may question the device used to measure your heart rate.

Entirely possible. My other theory is this. I know I felt tight and flat the first few miles and finally loosened up in the second half. So it's possible that instead of pushing hard later in the race, I mailed it in because the same pace was coming easier. And it was easy to convince myself I was still running hard. But I really don't know for sure.

A bit overtrained during the race, makes sense being in a marathon block