Power/HR ratio goes UP after ~1hr of training

I have noticed that ~1 hour into a training session, my HR actually starts to DECREASE per a given power, either while on a steady power Z2 ride or a set of intervals. The decrease is on the order of 5-10 BPM and is seen by Garmin Connect as in increase in Performance Condition, but I am wondering if it really is. This happens on long rides outdoors as well. Any thoughts on why this is?
Thanks in advance!

I have observed similar things: I see it as warmup time.

Seems that I am warmed up the best after 1-2 hours of easy (but not too easy) cycling. Then I hit my best times.

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Same. A good 40 minute into a workout and the engine finally hits its stride.


That’s pretty common. Interpreting heart rate data is not easy for this and many other reasons.

Look for negative decoupling.

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Training Peaks have a few articles on decoupling - positive and negative

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Here’s a 2 hour 10 mins Z2 outing yesterday. A nice amount of negative decoupling.

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