The body’s muscles and nervous system help control your breathing. The lungs are like sponges; they cannot move on their own. Muscles in your chest and abdomen contract, or tighten, to create space in your lungs for air to flow in. The muscles then relax, causing the space in the chest to get smaller and squeeze the air back out. Your breathing usually does not require any thought, because it is controlled by the autonomic nervous system, also called the involuntary nervous system.