There is a general rule of thumb - what you can do on your own in training, will predict what you are capable of in a race. I believe this to be true. If I am honest, I haven’t tried to test a 6 hour run race at the 3 hour pace I gritted through in training a few times, but I think up to reasonable distances, and especially around FTP and threshold testing, this is a fair statement.
So if we know:
- "CP" Stands for Critical Power or Critical Pace. In other words "The best effort you can do for" and the number is the minutes. So CP30 = "The best effort you can do for 30 min". CP60 would be the "best effort you can do for 60 min." and so on.
- what you do on your own you can do for 2x the duration in a race.
Then consider this too
Anytime you DOUBLE duration, you can predict a 5% drop off in output.
OK. So what does this mean when considering FTP tests on the bike?
Lets remember true FTP is what you can do for an hour (CP60) in a race. So, if you did a 30 min all out RACE that would tell you your (CP30), which you would then must subtract 5% to predict a CP60.
However, remember our rule above. What you ALONE predicts what you can do for double the distance in a race. So if you did a solo CP30 effort there would be no need to subtract the 5%.
This is also why I do not like testing for 20 min.
- Most happen in a group environment, so you have outside motivation
- Its not a clean doubling effect. So even if you do subtract 5% its still going to leave you a bit high in terms of FTP prediction
- A lot of people become good at “training for the test”. Therefore, its not a actual indication of their ME (Muscular Endurance)