Your body takes in air. This passes through the lungs and into your diaphragm. This is technically in your belly.
- Breathing system in a body
- Keeping in air
Swimming is a sport where you may want to keep some air in your body as you move. For example if you free dive, without equipment, you want to save air in your body. As you dive down you exhale a little of that air and as you return you expel more air. The good thing is as you change atmospheres, for example depth, when free diving you can gain more air as you go back up to the surface, thus keeping you in air until you reach the surface. Most people who want to float will also keep air in their diaphragm expanding it so that they can float on the surface of water. Likewise for those who want to sit down at the bottom it requires breathing out all the air possible so that they will sink to the bottom.
Yoga teaches one how to breathe better in order to balance the body. With Yoga you may expand your belly and then reduce it as you breathe in and breathe out. This allows you to learn how to keep air in and out as you move into a new position.