When Does Expiratory Muscles Contract?

Expiration muscles come into action when you force expiration. The expiratory muscles are the abdominal muscles and intercostals. It is rare if a patient is contracting abdominal muscles for quiet breathing and he is trying to force expiration.

Which muscles get contracted during expiration?

During forced exhalation, internal intercostal muscles which lower the rib cage and decrease thoracic volume while the abdominal muscles push up on the diaphragm which causes the thoracic cavity to contract.

What do the expiratory muscles do?

Muscles that helpful in expanding the thoracic cavity are called the inspiratory muscles because they help in inhalation, while those that compress the thoracic cavity are called expiratory muscles and they induce exhalation.