The diaphragm is the main muscle you use for breathing. When it contracts, it flattens and creates space in the chest so air can flow into the lungs; when it relaxes, air is pushed out.

What else it does

  • Helps with coughing, sneezing, vomiting, and childbirth by increasing pressure in the abdomen.
  • Helps prevent acid reflux by putting pressure on the esophagus.
  • Separates the chest cavity from the abdominal cavity.

Simple picture

Think of it like a flexible dome under your lungs: it moves down to pull air in, then springs back up to help push air out.

TL;DR

The diaphragm is a breathing muscle that also supports pressure-based body functions like coughing, urination, defecation, and preventing reflux.