Works only somewhat. Bending R, L, Front or Back shows respiratory cutoff. Lying down can reduce back expansion. The thorax and abdomen can support excess of 125 lbs. Need to blow 3 lbs.
Lips can resist air much greater than systems behind can provide.
Air pressure and quantity are function of absolute range. Pressure is the result not the cause. QED, tuba upper register requires less than one pound of interoral pressure. Even in high register, think wind, not pressure. There is no causative artificial stiffness, only a result Go by the air, not the appearance of the body Do not be afraid of exaggerated motion.