Marinades don't penetrate nor do acids tenderize,except for making the outer mushy. Papain, if not time controlled, will turn the meat to mush also. Sorry to be the bearer of bad news but at least you have something that will tenderize. Nothing is going to make tri tip melt literally like butter.
The diaphragm is the major muscle responsible for breathing. It is a thin, dome-shaped muscle that separates the abdominal cavity from the thoracic cavity. During inhalation, the diaphragm contracts, so that it's centre moves caudally (downward) and its edges move rostrally (upward).
Breathing is a task that involves some of the back muscles, which is why pain in the upper back when breathing is often a sign of a pulled or sore muscle. The upper back muscles may be injured, though lower back, abdominal, and diaphragm muscles are also often affected by every breath.