Originally Posted by DaveLeeNC

I suspect that you are correct - my guess at fat burning percent is probably way off (and probably varies greatly depending).

Regarding my FTP a few years ago when I measured it (20 min test) it was around 260. But I hit age 70 soon and back in 2018 I had a 6 month period of half or less my normal riding, my fitness fell off a cliff, and now despite going back to former training levels, 260W is and will remain a memory. I seem to be a solid 15W (maybe even 20) less than I was in 2017.

I did a couple of 30 minute Fartlek sessions the other day and they were both neither easy nor 100% of what I could do. And they both came out at 425'ish watts per half hour (850W per hour). Back in 2016 I did a solo century at 820 KJ/hour - like I said - memories only.

dave