I’ve found posts here that already kinda explain things, but I’m not sure they are specific to my question.
Rode tonight outside 50 miles in 2:45. Pushed pretty hard a good bit of the ride because the weather’s awesome and I was feeling great. But I don’t know that I was pushing 0.95 IF for 3 hours.
From what I’ve found, IF = NP / FTP
But how does duration play into that? I guess I’m confused on the use of FTP directly on a calculation for a 3 hour ride.
The calculation of IF is independent of duration. It’s simply NP/FTP like you said. Combining IF and duration gives you TSS.
Though if your IF for the ride came out to 0.93 for a 3 hour ride and didn’t feel pretty empty then your FTP is likely higher than you have it set at now.
In my experience I’ve found that IF and NP can be misleading for rides with a large power variations.
I was having some confusion about my easyish long rides being 0.8-0.85 IF for up to 5 hours, but if I looked at my NP it would be a number that there’s no way I would hold for that time.
I’ve also done a similar ride to you where my IF was 0.95 for 3 hours, it was a hard ride, but it was done a day after an FTP test so it’s unlikely my FTP was that wrong.
I think IF/NP is more about equivalent training stress than equivalent performance, but even then, it’s just an arbitrary calculation and would apply differently to different athletes. e.g. you might expect a crit racer to handle a higher NP that a time trialist relative to their FTP.
This seems like my experience yesterday as well. I also did an ftp test of sorts the day before too.
By Ramp test, my ftp is 249
In my best hour doing the Alp Du Zwift “climb” I avg 239 with NP 241, that was a totally solid effort with zero breaks. 68 minutes total up AlpdZwift.
My long ride yesterday was avg power 170 and NP 232.
Thanks folks who responded, I think I’ve had the epiphany I was looking for.