Originally Posted by
asgelle
It's not that you choose to do a 37 minute test, but rather you don't choose any specific time. The idea behind doing a Monod and freeing up the time is that the exact duration doesn't matter. Therefore, errors in pacing don't carry forward to errors in the results. To do an accurate fixed time test, the rider has to choose the effort that can be maintained for exactly the length of the test. To do a fixed effort test, pacing falls out of the equation. Pick a power that you think you can maintain for about 20 minutes and maintain this as long as possible. If it turns out the power chosen can only be maintained for 18 minutes or can be maintained for 24 minutes, it doesn't matter. Similarly for a power that can last about 5 minutes.
Good point. However, IMO the difference between failing at 19min and 21min can be explained away with associated errors and differences in mental toughness/motivation rather than a real difference in physiologically or biochemically defined "fitness." Or... if the tests purpose is to isolate and measure the aerobic system a small error in pacing is insignificant as the power/time-to-fatigue curve is pretty flat in that region.