Some people are tall while others are short. Some are top-heavy others bottom heavy. So the way that individuals carry their weight is different even though they may weigh the same amount numerically. Regardless, the key to being pain free is that gravity be our friend. If it is not, our muscles will spend an extraordinary amount of energy trying to counteract its force, which is constant. One consistency regardless of your theory of ideal posture is that the planes of motion should meet at 90° angles. We call this the Right Angle Fundamental. Basically, the body should maintain right angles around the planes of motion as it pertains to the load bearing joints. That's a loaded sentence, so what does that really mean?
Let's start with the planes of motion. There are three planes of motion and each is associated with a particular type of movement:
SAGITTAL PLANE - Divides the body vertically into right and left parts. Flexion and extension occur along the sagittal plane.
FRONTAL PLANE - Divides the body vertically into front and back parts. Abduction and adduction occur along the frontal plane.
TRANSVERSE PLANE -Divides the body horizontally into top and bottom portions. Rotation occurs along the transverse plane.
Regardless of where an individual holds their weight, ideal posture exists when their weight is carried by the skeletal system. In order for the skeletal system to effectively weight-bear, the three planes of motion should meet at 90° angles. When the right angle fundamental is met the body’s eight load-bearing joints are vertically and horizontally aligned to the line of gravity and the horizon respectively. In this case minimal effort is needed from the muscles and ligaments to maintain balance.
So what happens if the right angle fundamental is not met? Let's start with the fundamental concept of planal deviation. Imagine that each of the lines representing a plane of motion is a pane of glass. If one shoulder shifted higher than the other, the glass would break. This would be a transverse plane deviation. If the spine curved to the right from a scoliosis, the pane of glass would break. This would be a sagittal plane deviation. If the shoulders anteriorly rotated or the head jaunted forward from working too many hours at the computer, again the glass would break. This would be a frontal plane deviation. In each of these examples, the movement that breaks the plane of motion is perpendicular to the movement that occurs in the plane. Another important point is that the movement that occurs in the plane helps to strengthen that plane of motion. So, flexion and extension occur in the sagittal plane (and strengthen the sagittal plane), while abduction/adduction break the sagittal plane (but strengthen the frontal plane). Since our bodies are designed to move, a problem only occurs when our bodies don't go back to the right angle fundamental.
By assessing all three planes together we can assess alignment three dimensionally. A deviation in one plane affects all planes. As a result of these deviations, the skeletal system is no longer effectively weight-bearing and gravity is no longer our friend. The stretch sensors (muscle spindles and the golgi tendon organs) deep in the muscles detect excessive or sudden changes in muscle tension and the righting reflexes are invoked. There are five righting reflexes designed to restore optimal position when the body has deviated from it. The reflexes attempt to correct the deviation through a signal relayed from a reflex mechanism that causes a muscular contraction.
In the case of an athlete, such as a gymnast, the righting reflexes are strong and enhance performance by allowing the athlete to overcome the effects of sudden head movements. However, once the righting reflexes function improperly, the body enters into a state of compensated motion. The muscular system will adapt any way necessary to maintain balance against the force of gravity and to keep the eyes parallel with the horizon. For example, if a client has an elevated right hip (transverse deviation) their body may compensate by elevating their left shoulder (transverse deviation), bowing their spine (sagittal deviation) and anteriorly rotating their hips and/or shoulders (frontal deviation) to keep their eyes parallel with the horizon. Ideally, we can move our body through its full range of motion. The agonistic and antagonistic muscle groups are balanced and hold the body in proper alignment. If this is the case the body can typically move efficiently and effectively in all three planes of motion. However due to physical or emotional trauma, poor ergonomics or attitude, posture may become compromised. In this case the body’s ability to move properly through all three planes of motion also becomes compromised, further affecting the balance and structure of the soft tissue system (muscular, fascial, etc).