The muscles down the midline of your body are involved in the valsalva maneuver. Your mouth, larynx, abdomen, diaphragm, sphincter, et al. Imagine yourself pusbing a heavy piece of fur iture across the room. You can feel these muscles engage. These are the muscles Bill Parry says to keep lose. I dont want to put words in his mouth because it was a long time ago, but he said it's easier to achieve this by focusing on the sphicter muscle. By keeping it loose, the rest of the muscles kind of follow.