In Myokinematic Restoration, James Anderson talks about how tightly woven anatomically the psoas major is into the right diaphragm leaflet. Can we then assume that activation of the right psoas can be used and is advantageous to use as a method of activating the right diaphragm/pulling it down to enhance right intercostal expansion?
The interesting thing about the psoas major and the diaphragm is that they have similar influence on the spine in the sagittal plane, but they have an opposite influence on the spine in the transverse plane. In other words, in the transverse plane, the right psoas major compliments (or is agonistic to) the left leaflet of the diaphragm; and the left psoas is agononistic to the right leaflet of the diaphragm. They work with one another through their “tightly woven” attachments ipsilaterally in the sagittal plane to enhance the extension activity of an extended patient, but work with each other contralaterally across the anterior vertebral bodies in the transverse plane. So, if you activate the right psoas, you are enhancing the sagittal influence of the right diaphragm leaflet and the transverse influence of the left leaflet (something that is desirable in both planes at both of these sites).
As far as using the right diaphragm to enhance right apical expansion is concerned, its incorrect to view it that way. In fact, it is the torsional respiratory influence of the left diaphragm (not the right) that is primarily responsible for expansion of air into the right chest wall and mediastinum.