Cournand lecture: Mechanical action of the abdominal muscles.
The abdominal muscles, by causing a rise in abdominal pressure and a cranial displacement of the diaphragm, 1--deflate the lungs (minimize the increase in FRC which normally occurs when adopting the standing posture), 2--exert an expanding force on the lower rib cage, which may counterbalance or even dominate the insertional (expiratory) force they exert on the lower ribs by way of their insertions, 3--improve the pressure-generating ability of the diaphragm. In addition, because they prevent the diaphragmatic dome from descending during inspiration, they also improve the rib cage expanding action of the diaphragm.
D000009:Abdominal Muscles / Q000502:physiology*; D000818:Animals; D001696:Biomechanical Phenomena; D003964:Diaphragm / Q000502:physiology; D004285:Dogs; D004576:Electromyography; D006801:Humans; D007366:Intercostal Muscles / Q000502:physiology; D008168:Lung / Q000502:physiology; D009119:Muscle Contraction; D011312:Pressure; D012119:Respiration; D012272:Ribs / Q000502:physiology; D013314:Stress, Mechanical; D014939:Work of Breathing