The mantra is, " when power exceeds FTP, fatigue will occur much sooner, whereas power just below FTP can be maintained considerably longer".
However, if you look at power duration curves using maximal data, people can maintain a power above FTP for up to approximately 60 minutes, some for over 60 minutes, almost 70 minutes and others only approximately 30 to 40 minutes, but on average just under 60 minutes. But after approximately 60 minutes, when power has dropped below FTP, wattage continues to fall at approximately the same rate as it did from approximately 20 minutes to approximately 60 minutes. It does not plateau or become steady state but continues to fall.
According to the dogma, we are unable to maintain power above FTP for very long - if this is the case why are we able to maintain a power above FTP for so long?
If FTP is what it is claimed to be, we should be able to maintain power just below FTP for longer. But this is not seen on the power duration curve. Power continues to fall beyond approximately 60 minutes at approximately the same rate as it did before between approximately 20 and 60 minutes.
There isn't a threshold on the power duration curve, there isn't an area on the curve at around the 60 minute mark where power falls off at a substantially slower rate, there isn't a threshold like part of the curve and it is not true that we can't maintain power above FTP for very long, because we can produce power slightly above FTP for almost as long as we can maintain FTP.
I don't dispute that power at FTP correlates closely with MLSS, or other markers just that the threshold does not seem to be visible on the power duration curve.