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The sternocleidomastoid are muscles that are considered accessory. They are active for inhalation when needs increase or during high lung volumes as in hyperinflation. These muscles pull the sternum up and increase the size of the upper rib cage in the AP dimension, sometimes taught as pump handle elevation. These accessory muscles are affected by the position of the diaphragm and changes in the ZOA.10Kyndy The diaphragm displaces the abdomen and the rib cage equally during quiet breathing. If the resting tone in the oblique abdominals is insufficient, more than half of the expansion would go into abdominal expansion allowing for superior migration of the anterior aspect of the rib cage. This would decrease the ZOA, change the muscle lengths…show more content…
Weakness in the abdominals can have a snowball effect on posture and will be discussed later.1 Like the diaphragm, the transversus abdominis modulates its activity for both postural and respiratory functions, unlike the other abdominal muscles. It is not active during quite breathing but becomes active as the demands for expiration increase. Its EMG activity is therefore out of phase with EMG activity by the diaphragm. 8,11Hodges/Gandevia 2000 and Hodges/Gandevia/Richardson Various studies have shown that the diaphragm and the transversus abdominis simultaneously contract prior to movements in the extremities. Hodges et al demonstrated this co-activation 20ms prior to the activation of the deltoid when the subject was asked to move an arm into flexion.8 Hodges/Gandevia/Richardson. Hodges monitored the diaphragm by measuring the length of the ZOA because it+ is closely associated with the length of the diaphragm. He believed that the diaphragm+ was contributing to postural stability by, “maintaining the hoop-like geometry” of the abdominal wall.Hodges19 Vostatek stated that the diaphragm was contracting in order to provide abdominal pressure for stabilization of the spine. He also stated that the ribs needed to stay down and only expand out to the sides during inhalation in order to maintain
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