(a) Abdominal breathing: It is calm breathing which drives mainly by movements of diaphragm. During expiration, flattening of diaphragm, a pressure is creates on abdominal organs. Due to this abdominal organs also create pressure on abdominal wall, thereby abdomen swells. It becomes normal in expiration. In this swallowing and flattening of thorax is much less. (b) Forced Breathing: It is also called deep breathing. During this the intercostal muscles and abdominal muscles also contract which greatly reduces the volume of thoracic cavity thus exerting additional pressure on the lungs. The contraction of internal intercostal muscles decreases the volume of thoracic cavity by pulling the ribs and sternum dorsally and downward whereas the contraction of abdominal muscles causes abdominal organs to press the diaphragm upward which in turn bring about additional pressure on lungs as a result of which more than normal amount of air is thrown out. During prolonged exercise, exhaustion or nervousness we take deep breath which is a voluntary activity. During this time, not only diaphragm gets fully contracted but external intercostal muscles also undergo complete contraction which increases the volume of thoracic cavity 20 - 25% more than during the usual breathing and so 20 - 25% more air is filled in the lungs.