Understanding why/how Tensions build up in Chest and continue to the Head
In order to maintain the center of gravity over the feet or one foot when the other is off the ground chest is moved to different positions. Even the position of the arms and head will require small adjustments.
With decades of experience it has become apparent that this is accomplished best by what is considered an insignificant muscle pair called psoas minor. This muscle originates on the front of the spine overlapping the last thoracic and first thoracic vertebra. It inserts into the front of the pelvis just in front of the hip socket. When functional as intended it maintains tension so that the top of the lumbar is centered over the pelvis lengthening on one side and shortening on the other to move the center over the hip socket.