I am an amature adult player (started when I was 40). For years I've been trying to solve an embouchure problem and I am now at the point of total frustration. The problem is that my embouchure is literally intermittent. For many days in a row it will be fine, well controlled, and it is a pleasure to play, top note is a none-strained high-C. The only thing that stops me is fatigue which I don't push pass. When I am at the point when I can no longer form and support a note properly I put the trumpet down for the day. Then, based on no pattern that I can discern, for two or thre days in a row I literally can't form an embouchure. My clean range is reduced to approximately the low-G to the first E on the staff. And no amout of warming up with slow, long, easy notes, solves the problem. It is as if one day you could use your legs to run an jump and the next day you are too weak to walk accross the room.