Kalijah, we still have to balance science and common practice. There are quite a few very "physical" lead players that even use ADDITIONAL force on the breathing mechanism with a technique called the wedge. I am talking about very successful pros. There must be several alternatives. if we want to change pitch while playing, we only have two mechanisms: the tension surrounding the lip tissue and the intensity with which we blow. In fact the Germans have a term for this called "Überblasen" or overblowing. An advanced embouchure does not need the extreme changes in tension or air pressure that "weaker" ones do but still both methods work even when applied to "dummy" lips. That is often attributed to the stability, control and flexibility of the aperature. I believe there is an additional force of compression of the lip tissue caused by increased "blowing" pressure and the resultant back pressure from the horn. That will "clamp" the lips with an air cushion. We have a standing wave in the horn that will tend to stay at whatever frequency it currently is until we "disturb" it. The above mentioned mechanisms will accomplish exactly that.