irey,
I’m glad you asked this, it brings up an important issue when using power.
Power meters do not have to be accurate. They just have to be consistent. If your power meter says that your rFTP is 1,000,000 watts, that’s fine. As long as your displayed power is 1,000,000 watts every time for that same actual output. You would put in 1,000,000 watts as your FTP into the zone calculator, and your zone 2 would be 700,000 to 830,000 watts.
There is no international organization that validates accuracy of power meters. It’s up to the manufacturer, and they are going to be different. I once did a cycling interval workout with a hub, chain, crank, BB, flywheel, and pedal-based power meter connected to 6 separate devices. Same workout, same output… 30 watt difference between the lowest and highest watt reading for the same intensity. Which one was right? Technically, only one of them, but we’ll never know. For our training purposes, all of them are right a long as they are consistent.
Finally, run power will always be higher than cycling power. That is normal. I’d expect to see at least 30 watts difference between your cycling and run FTP.
However, 425 is high for an easy run, that’s for sure. But, if you are getting 425 for every single easy run, then I’d have no reservations using it. The key with the HRM is to ensure the strap is tight and consistent between runs. That might get it back down to a more expect value for an easy run.
David