Learning to be aware of your breathing, and to control your breathing is often considered one of the first steps toward controlling the physical and mental effects of stress. Chest breathing is shallow. The shoulders often rise with each breath and only the chest expands. This results in poor exchange of stale air for fresh air. This also contributes to fatigue, because the body's cells don't receive the required oxygen necessary for effective functioning.
People tend to increase shallow chest breathing when stressed.
Conversely, shallow breathing can contribute to feelings of stress. To do this you . need to use your diaphragm. The diaphragm is a large sheet of muscle, like a piece of rubber balloon, stretched over the bottom of the lungs. When breathing is relaxed, the diaphragm expands down on the in breath, creating a negative pressure that pulls air into the lungs. On the out breath, the diaphragm relaxes back into its original position, pushing air out the of the lungs.