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).
Considerations. The wall of your chest is flexible. This helps you breathe normally. Stiff tissue called cartilage attaches your ribs to the breast bone (sternum). The intercostal muscles are the muscles between the ribs. During breathing, these muscles normally tighten and pull the rib cage up.