Cardiac Drift (or why use power)

Just downloaded my t6 data (not really interested in HR, but have been tracking EPOC to see how it scales with power for no-power-able rides).

 

Now, if you read last nights post, you know I did 4x10 @ ftp ramp downs (starting @ the top of L4 and ramping to the bottom so the average is exactly FTP).

 

Something you notice not so much in the power file but becomes obvious in the HR trace only is cardiac drift:

 

Click to see full size (like all of my images here).

 

See how the HR during each interval steps up?  But the workload is identical (the averages and normalized powers for each intervals are within 3w of each other - it was in erg mode).

 

How do you think power would have varied if following the same workout description but used HR as the pacing tool?

 

Food for thought.

 

-g