Just like any other muscle, your diaphragm contracts and relaxes. Not only is it the primary muscle designed to help you breathe, but it also creates stability and power. Training this muscle alone can increase both your endurance and your athletic explosiveness.
When the diaphragm contracts it pulls down lower on the ribs and the spine. As it pulls down air fills the lungs which sit directly above the diaphragm. When the diaphragm relaxes and returns to its rested state it naturally forces air back out of the lungs. Other muscles play a part in the exhale as well which we will look at another time.
When the diaphragm pulls down it presses down on all of your organs and the entire abdomen. This creates a great amount of pressure. This tension helps to keep the spine and entire torso rigid. Almost all sports and exercises use this pressure to generate high amounts of force and to help the body support heavy loads.
This single parachute-shaped muscle in the middle of your body is the most important muscle for any athletic activity yet you have likely never thought to train it as much as your hamstrings or other muscles. To begin doing so start with back breathing. Check out the video below for a demo!