Breathing & its different types
Physiologically breathing is of 2 types: Abdomino-thoracic and thoraco-abdominal. Females have thoraco-abdominal while males have abdomino-thoracic breathing.
There is 2 reason for thoraco-abdominal breathing in female first is that females have a greater inclination of ribcage than males. This causes the intercostal muscles to raise the ribs more effectively so increasing the action of intercostal muscles accounts for more prominent thoracic breathing also due to the greater inclination of the rib cage females have lesser thoracic dimension.
But why do females have more inclined rib cages? Unlike males where the rib cage plays a role to accommodate lung volume displacement only. In females, the rib cage serves to do all purposes to accommodate both lung volume as well as abdominal volume displacement. This abdominal volume displacement is a functional adaptation to pregnancy. It minimizes the distending effect of the pregnant uterus on the lung and also decreases abdominal pressure.
The second reason is that diaphragm length is 9% shorter in females than in males.
So what about the males, who have more horizontally oriented rib cages?
Males have abdominal-thoracic because their diaphragm is longer than females, which is 9% larger. The males have more horizontally oriented rib cages. So there is inefficient action of intercostal muscle, making thoracic breathing less prominent in them. During inspiration, the diaphragm descends, pushing the abdominal viscera down and raising the abdominal wall. Thus abdominal movement becomes prominent and contraction of abdominal muscles facilitates respiration.
Diaphragmatic breathing could be compensation for inefficient action of intercostal muscles in males. The greater diaphragmatic action in males is linked to male thoracic morphology which is wider at the corner part, greater medial-lateral expansion of lower lungs, and a more pyramidal shape of the male lung.