Anatomy of Alignment:
The median plane is the slice that splits the body into left and right halves. Straight down the middle, our true midline, with the body balanced either side.
The median plane is a straight line when seen from the front or back, and a 2-D shape when viewed from the side.
Median = Midpoint, middle.
Plane = A flat, two-dimensional (2-D) surface.
The body must be "correctly arranged" to create the median plane, where:
Our midline anatomy that should align on the median plane includes the linea alba at the anterior (front) of the body and the nuchal ligament and supraspinous ligament at the posterior (back) of the body.
The first step in aligning the body and creating the median plane is to work with your Base-Line muscles: pelvic floor Base, rectus abdominis Line.
Your Base-Line muscles provides sensory feedback about the relative positioning of your midline, so focusing on using these muscles helps to increase awareness of your sense proprioception (your sense of position, motion and balance).
Sensory information about the positioning your midline anatomy is provided by many other sources too. All will help to guide you in how to move in order to increase alignment, and improve your posture.