Training Zones?

Well, I've now trained one session with my zones based off of my LT field test, and I already see a problem with using heart rate. Yesterday, I went to roughly the middle of Zone 2 (endurance) according to power and my heart rate just barely hit the minimum for that zone. My perceived exertion was also telling me I was in the right spot, so I didn't go any harder to force my HR up.

Afterward, I plotted all of the data I have from rides where I measured both HR and power (unfortunately, only 4 so far, including my test... I don't always wear the HRM, and no power if I ride outside). Then I plotted the training zones I was using. The training zones are based on the table shown at the Cycling Peaks website.


It looks to me like my power numbers are OK relative to the training zones, but that my HR numbers are low. I think the most likely explanation is that my HR was higher than it probably should have been for my test. If I take the training zone line and shift it down by about 10bpm, it makes the data from my other three rides look OK. Also, I discovered that if you project this new line back to zero Watts, you get 42bpm, which is just a few beats off of my resting (lying down) HR. Maybe it's just a coincidence, but this kind of relationship makes sense to me.


So, my plan is to shift my HR numbers down 10bpm and see how things go. I'll try to be more diligent about strapping on the HRM when I ride on the trainer, to take data if nothing else. We'll see if my test at the end of this month gives me a lower HR.