Both... your chest expands - pushing your rib-cage out, and your diaphragm pushes downwards - forcing your organs to move outwards slightly.
inhaling
The diaphragm relaxes and reduces the space in the chest cavity.
When you breathe, the actions of your rib muscles and diaphragm expand or contract your chest. As a result, air flows in and out.
You can observe respiration by looking for signs such as inhaling and exhaling of air, movement of the chest or abdomen, and listening for breath sounds. Additionally, you can feel for air being expelled from the mouth or nose and check for a pulse to ensure circulation of oxygenated blood.
it separates the chest cavity from the abdominal cavity. other wise they would e everywhere! please reply to this by saying if it helped and what you thought of it (you can do this by 'improving the answer')
When breathing in, or inhaling, the diaphragm contracts, or tightens. When exhaling, or breathing out, the diaphragm expands, or loosens.
The diaphragm relaxes and reduces the space in the chest cavity.
The air pressure in your chest cavity increases when you are exhaling. For air to leave your lungs, it must be at a higher pressure than the air outside. Your diaphragm pushes up against your chest cavity causing the space in your lungs to get smaller. If the volume decreases, the pressure has to rise. Don't believe me? start exhaling, then close your mouth. Your cheeks will puff out because the pressure inside is greater than the pressure outside.
The seated incline chest press exercise helps strengthen the chest, shoulders, and triceps. To perform it properly, adjust the seat and incline to a comfortable position, grip the handles with palms facing forward, and push the handles away from your body while exhaling. Lower the handles back to starting position while inhaling. Keep your back flat against the seat and maintain control throughout the movement to avoid injury.
When exhaling, the diaphragm relaxes and moves upwards, causing a decrease in the volume of the chest cavity. This increase in pressure pushes air out of the lungs.
During inhalation, the diaphragm contracts and moves downward, allowing the lungs to expand and fill with air. This creates a vacuum in the chest cavity, drawing air into the lungs. During exhalation, the diaphragm relaxes and moves upward, forcing air out of the lungs.
The sitting chest press exercise helps strengthen the chest, shoulders, and triceps. To perform it properly, sit with your back straight, feet flat on the floor, and push the weights away from your chest while exhaling. Keep your elbows at a 90-degree angle and avoid locking your elbows at the top of the movement.