What is the most important muscle to aid in breathing?

The diaphragm is the most important muscle to aid in breathing because it is the primary muscle responsible for the process of inhalation, which is vital for bringing oxygen into our lungs. The pectoralis major is a chest muscle that is mainly used for arm movements and would not directly contribute to our breathing. The intercostal muscles are located between the ribs and are also involved in breathing, but they primarily assist with expanding and contracting the rib cage, rather than controlling the movement of the diaphragm. The abdominis muscles, which make up the abdomen, assist with exhalation by compressing the organs in the abdominal cavity, but they are not the main muscle involved in the active process of breathing. Thus, the diaphragm is the most important muscle for breathing.