Difficulty maintaining power at recommended cadence. Is recommended or preferred cadence better? I find that it's easier to maintain my power at a lower cadence. For example, 75 RPM versus 95 RPM. I'm using TrainerRoad. Recently, I've experimented with a higher cadence. 

On one of the workouts, I could only complete 3 of 5 sets. It felt like hitting the wall which never happened to me before on TR.



During FTP tests, I felt that I could test higher for the interval with a cadence that's almost 10 RPM lower.
See VO2 Max 2 and VO2 Max 3.


Even for a recovery week's endurance workout, my hip flexors surprisingly lasted a little more than enough for the workout. Maybe those muscles were my weakest links.



Is it possible that my legs were heavy, making lower cadence even more efficient? My thigh's circumference is 20" and my shin's circumference is 14.5". My height is 5 feet 7.

Is it better to do an FTP test with the ideal cadence or the most efficient cadence (the one that allows you to produce the most power)?

For my workouts, should I select the cadence that works best for me regardless of their recommendations?

Is it likely that my FTP was too low for a high cadence?
GCN did a couple of videos on the subject (1, 2) . In the first linked video, the presenter said that "what current research seems to point to is that is that people ride at their energetically optimum cadence when they're toward their maximum power output. However, they tend to ride at too high a cadence when they're riding at lower intensity." Also that everyone's different, leg size factors into cadence, etc.

Sounds to me like you should do what your body is telling you to do. You're obviously experienced enough that you're not going to blow your knees out riding stupid-low cadences.