Two ways of creating air pressure
Air flow from the lungs is created when the pressure inside lungs (your chest) is greater than outside. There are two ways to create this pressure.
- Take a deep breath and sigh. The weight of your body (gravity) creates pressure inside your chest and the air escapes without effort on your part. See Yawn and Sigh
- If there is any air in your lungs, you can engage the muscles of your upper body to increase the pressure within your chest (thorax). This will also cause the air to escape. Engaging muscles requires some effort.
It is useful to be able to master both of these methods. Visualizing lung capacity will help us to understand when these different methods are appropriate.