It’s a popular misconception that FTP is defined as the power someone can hold for a hour. Rather, FTP is power output at LT2 or some steady state around that intensity, called “ functional threshold,” by Andrew Coggan et al. They observed that the trained athletes in their studies could hold that output for something like an hour. However, the population range is really about 40-70 min for trained athletes and likely shorter for some of us “alter kackers.” A 60 min all out effort to complete exhaustion is extremely difficult even for elite athletes under anything but competition conditions, which is why 60 min for time to exhaustion at FTP was always just an approximation and why Coggan and coworkers validated the 95% of 20 min power estimation technique.