July 15th
By failure, I assume you mean exhaustion. If so, your durations won't be exactly 20mins. Anyway, testing to exhaustion is my preferred way to identify data points on my MP curve. As to extrapolating your FTP (60MP) from any single data point, it's tricky unless you have a good idea of your full MP curve from multiple tests to exhaustion at different durations. This is because the anaerobic work capacity to aerobic capacity relationship varies quite a bit between individuals. My suggestion is to do a couple of other MP tests to exhaustion (e.g., 3min and 8min) and use the Monod Critical Power Model to estimate max sustainable power at any duration. One caveat: note that the Monod Critical Power Model tends to overestimate MP at longer durations. Here's a free Monod Critical Power calculator:
Thanks. I have used Monod before, however as i'm much stronger over 15-20 minutes than I am over shorter anaerobic periods, Using the power cure from files I have (3 & 8 Minutes), the estimation of CP value is 308w, which is in line of what GC gives me. It is also the same if i use 20 minute data rather than 8minute.
Well, it's generally not a good idea to cherry-pick values from your ride files for the Monod CP Model. As to how good the estimate is, it really depends on your purpose for the estimate. If it's to set power targets for training rides, it should be good enough although personally I prefer taking 90% of my recent max power for a given duration, a methodology I use across the full spectrum of the power-duration curve. If it's for the purpose of setting a target power for an individual time trial of an estimated total duration, I'd suggest doing a ride to exhaustion at what the model outputs. I use the Monod CP Model regularly and the primary shortcoming is that it tends to overestimate max sustainable power for long durations. So, I discount estimates > 60mins when I use it. BTW, I think too few cyclists take advantage of testing to exhaustion. It sounds scary, but it's actually not. I feel great within 15 minutes of a test to exhaustion. And, when you use the Monod CP Model, it doesn't matter what the duration to exhaustion is. You get a valid number (in seconds), whatever the number is. You don't need 3mins exactly. 2:48 or 3:27 or 4:08 work just fine.
