During which phase of breathing does the diaphragm push air out of the lungs?

The diaphragm plays a critical role during expiration, which is the phase of breathing where air is expelled from the lungs. During this phase, the diaphragm relaxes and moves upward into the thoracic cavity. This upward movement decreases the volume of the thoracic cavity, leading to an increase in pressure within the lungs compared to the external atmosphere. As a result, air is pushed out of the lungs due to the pressure difference.

In contrast, inspiration is the phase where the diaphragm contracts and moves downward, increasing the volume of the thoracic cavity and drawing air into the lungs. The terms resting and ventilation refer to different aspects of breathing and do not specifically identify distinct phases like inspiration and expiration. Ventilation is a broader term that encompasses the entire process of moving air in and out of the lungs, rather than focusing on the mechanics of either phase. Thus, expiration is the correct choice as it directly involves the action of the diaphragm pushing air out of the lungs.