On left low trap and serratus securing the spine...
How does the left low trap and serratus “secure the spine” (as mentioned for management of superior T4 following treatment of it)?
The left lower trapezius muscle rotates the mid thoracic spine to the right as it assists with internal rotation of the left ribs that are attached to the thoracic spine, and movement of the same ribs posteriorly. An individual with a superior T4 syndrome is experiencing difficulty in moving the right first and second ribs into internal rotation and the first and second ribs on the left, concomitantly, into external rotation upon left trunk rotation. During right trunk rotation, all the ribs on the left rib cage need to simultaneously rotate into internal rotation and likewise all the ribs on the right rib cage need to rotate into external rotation. After performing a right subclavius manual technique to increase the length of the right subclavius muscle, spinal rotation to the left is needed to take advantage of implementing internal rotation of all the ribs on the right, since now, ribs one and two on the right can internally rotate and ribs one and two on the left can externally rotate.
By reaching forward with the right arm to activate the right low trap and right serratus anterior for left spinal rotation and scapular movement on the thorax, you re-align all the ribs by moving the right ribs into internal rotation. Reaching forward with the right arm a little more upon exhalation would help this process even more. Then, reverse and move the left arm forward, upon exhalation, to rotate the spine and rib cage to the right. Every time you inhale, with the left arm reaching forward, expand or move back the left posterior ribs a little more. By moving the left ribs back on inhalation with the left serratus anterior, as the spine is being held or stabilized in right trunk rotation, the diaphragm can assist with air flow into the left posterior chamber of the left lung promoting universal posterior thoracic expansion during right trunk rotation without losing internal rotation provided by the left serratus anterior of the left lower ribs.
From this point on, your right lower trap will now experience more stabilization from the left lower and mid ribs and the left lower trapezius during alternating arm reaching or trunk rotation. In essence, the left lower trap is now serving as an eccentric stabilizing force for left posterior thoracic expansion during left heel strike and left arm reach. Without the left lower trapezius and left serratus anterior functioning upon left arm reach, the spine would not need to rotate to the right with the left lower trapezius because it may already be oriented to the right because of lost left posterior thoracic expansion and inability to open the apical or posterior left lung and chest wall. The left first and second ribs staying in an internal rotated state, limits the ability to expand the upper posterior mediastinum or lung tissue. Therefore, following the right subclavius manual technique used for treatment of a superior T4 syndrome, alternating right lower trapezius and right tricep with left lower trapezius and left serratus anterior is highly recommended for spinal stabilization during alternating trunk rotation or gait.