When you search online you get conflicting information. I’ve seen it stated that CP is c.6% higher than FTP but that doesn’t make sense to me as CP is the aerobic contribution. I’ve also seen it stated that CP is lower than FTP.
My mathematical understanding:
Take a rider with CP = 300W and W’ = 25,000J
60 minutes = 3,600 seconds, therefore 25,000J spread over 3,600 seconds is 7W
Therefore, this rider could ride at 307W for 60 minutes
Repeating the above for 40 minutes or 70 minutes, you get 310W and 306W respectively, so as far as I can see, CP should be a figure that is a few percentage points lower than FTP
Personally, I use CP for my training. It’s far more helpful for me to understand my capabilities across multiple (sub 60m) periods and it fits in better for a season full of road and crit racing. But am I misunderstanding the relationship between FTP and CP?
Its a can of worms/ popcorn but for me FTP is a number to train to and there’s some debate whether you can actually hold it for an hour, especially as you age, whereas CP is the actual number an individual can hold for a given period of time (not necessarily an hour). So in my thinking FTP might be higher than CP, at the extreme the same for an hour; but for periods sub 1h CP might be higher than FTP, especially over short durations, but I’m no coach
My understanding is that the maximum power you can sustain for a given period is a function of your CP plus your W’. So using the example rider in my first post, for 20 minutes, they could hold 321W, but that’s still comprised of a 300W CP with the other 21W coming from the 25,000J spread over 1,200 seconds. So the CP figure doesn’t change whether the period is under or over an hour.
(Some people occasionally refer to things like CP20, which is different to what I’m trying to focus on in the Critical Power and W’ model!)
The problem for me with CP is the multiple definitions for interpreting the power curve graph.
. I can fined no standard for where/when CP should be measured based on time. please let me know if you do find one. Most academic definitions are require on lab vo2max and Gas Exchange Threshold testing.
eg “ Critical Power is your highest sustainable rate of aerobic metabolism (without a continual loss of homeostasis). It equates to roughly 30-40 minutes of high-intensity cycling” -RCA
The problem within that definition is it limits the time component less than 60 min which in theory would give a higher number than FTP
Academically : “ CP was originally defined as the external power output that could be sustained ‘indefinitely’ or for ‘a very long time without fatigue’ This definition should be considered theoretical, however, since it is clear that no exercise can ever be undertaken indefinitely. Rather, it is now understood that CP separates power outputs for which exercise tolerance is predictably limited (exercise >CP which may be sustained for a maximum of perhaps 30 minutes.
30 min would give more than ftp presumably, But again this is not specific to cycling
Sidestepping your analysis, lets start with some basics.
In Skiba’s book he references a study that puts CP at the highest power that most can sustain for 20-40 minutes. So FTP is lower, unless you feed the CP model some longer efforts and use GoldenCheetah’s (GC) Extended CP.
I’ve compared my self-assessed FTP to GC’s Extended CP and they are within a watt or two of each other. As far as I’m concerned, FTP and CP are essentially the same if you properly feed the CP model. Otherwise if you only use something like 3 minutes, 6 minutes, and 12-14 minutes, in my experience, the CP model overestimates the tipping point between stable and unstable.
In the book Skiba tries to dismiss FTP in his misunderstandings section by trotting out the “strongly correlated with LT1” argument and missing the entire point that it is a field test for maximal lactate steady state - the very thing that defines a separation between stable and unstable physiology which is the same as what CP purports to do! Same same if you aren’t in a room of physiologists trying to debate words and defend mathematical models that have limitations and suffer from garbage in, garbage out.
