the diaphragm to lengthen or shorten the chest cavity, and the elevation and depression of the ribs to increase or decrease the diameter of the chest cavity. These movements depend on the functions of the upper abdominal muscles. Overall, the muscles that elevate the chest cage are muscles of inspiration (inhalation), and those that depress the chest are muscles of expiration (exhalation). (Health Central) If forceful expiration is require
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