Best Answer: There are two main sets of muscles involved in breathing. The first is the diaphragm which is a two part leaf muscle that pulls down and flattens, when this happens it also pulls down on the bronchials of the lungs and helps to straigten them out so that the air has a more laminer shot into the lungs.he first is the diaphragm which is a two part leaf muscle that pulls down and flattens, when this happens it also pulls down on the bronchials of the lungs and helps to straigten them out so that the air has a more laminer shot into the lungs.