Why is my heartrate initially higher in a longer ride?

[roleypup]

What time of the day were you doing these rides? If you were feeling too-cold at the start but then warmed up & felt comfortable… I wonder if that would explain HR drift.

Also, check your cadence profile over the whole ride. If your self-selected cadence drops over the course of a ride, then it will encourage a slight drop in heart rate.
Lower cadences cause:

1. Lower muscle pump
2. Increased pedalling force for the same power output, ensuring greater recruitment of type-2 fibres → less oxygen is required for the same power output, therefore less cardiac activity is required.

This thread has a more in-depth explanation:

Cadence vs HR at a constant Power - is there an explainable relationship?

I’m completing an adaption week, so had a low power ‘Andrews’ session. In the last 15 minutes instead of sticking rigorously to the plan, I decided to test this relationship, but would like to know more what it tells me. I set my Power at 75% and held this rigorously. Over 5 x 3 minute intervals I stepped up the cadence twice then stepped it down twice and let TR monitor my HR. The results: Cadence - 87 … … 96… … …105… …96… … 87 HR… … 102->112… ->117… . ->123… ->120… ->115 I wa…