Is it effective to do outside MTB training with power measured as RPE?
Yep, I’ve used this and also used %HR(threshold) as a way to approximate %FTP. I know that HR is not supposed to be that reliable but got consistent bumps in FTP ramp tests throughout. Switched to PM now but dont feel I lost heaps using %HR only (just chose that as I wasn’t confident with RPE), it is more about just selecting appropriate trials to keep you in the “zones”
For my outdoor rides I use a Garmin Oregon which doesn’t connect to power meters but does connect to HRMs. However the devices I have (Garmin and Lifeline) are very intermittent with how they work - sometimes I’ll get a full couple of hours of data, other times I’ll get 20-30mins then it flatlines at whatever value the last genuine value was.
After a while if you log both RPE and HR data you get an intuition for how a ride feels, particularly below LT1/VT1. For VO2max/anaerobic work, just go as hard as you can for the interval period. Threshold I go with the Chris Boardman analysis:
Can I maintain this? If yes then I’m not going hard enough, if no then I’m going too hard, if the answer is “maybe” then I’m about right.