Arches and Angles
Newton’s first law of motion states that an object tends to remain in its current condition until acted upon by outside forces. For example an object sitting still remains still until pushed or pulled, and a moving object maintains its path until outside forces alter its course. This action is referred to as inertia.
The outside forces acting upon an object in motion can be obvious, such as gravity when a baseball is thrown. Immediately after releasing the ball gravity begins to push the ball downward and friction of the air over the surface of the ball cause it to curve. Gravity and friction are two outside forces that overcome the forward inertia of the ball. These outside forces make it necessary to throw the ball in an arc in order to hit the intended target and also combine to allow the pitcher to throw both breaking pitches and fast balls.
Another example of outside forces that influence forward inertia is that of a marble traveling through a tube. If a marble is propelled through a tube it will follow the path of the tube, as the tube curves so does the marble, the walls of the tube are the outside force that act upon the forward inertia of the marble.
Mechanical engineers use this law of motion when constructing a building. The weight of a building, its occupants and fixtures are in motion downward due to gravity. Since all of these things are being pushed straight down their motion is in a straight line. To keep the size of building support structures reasonable, as well as their cost, the mechanical engineer uses arches and angles to divert this downward motion and spread it out over many smaller support beams.
The muscular-skeletal system of the human body is an amazing combination of the marble in the flexible tube example, (muscles, tendons and ligaments) and the arches and angles of the building example, (bones and joints). We have the ability to alter our structure continuously to adapt to whatever motion, or energy, of an object pressing or pulling us.
In taijiquan we refer to five bows or arches in the body, they can clearly be seen when performing the standing meditation posture embracing the pillar. The first arch is formed by drawing a line from one foot to another, up the leg through the pelvis and down the other leg. The second bow or arch is formed by drawing a line from one hand along the arm across the chest down the other arm to the opposite hand. The third arch is formed by tracing a line down the arm through the arm pit and down the same side of the body. The fourth arch is found in the knee by following a line up the back of the leg from the foot to the hip. The fifth arch is formed by the natural curve of the spine.
By maintaining these arches, even if very minutely, you will be able to hold your structure and withstand outside forces or energies. The collapse of any of the arches will precipitate a domino effect and an eventual collapse of the whole body. When this happens you will need very strong muscles to recover; this is also the point where injuries are most likely to occur due to the external energy or your own muscular forces exerted on the joints, as either of these may exceed the strength of the ligaments holding the joint together.
The natural arches of the body give us strength of structure and the waist gives us flexibility. It is through the flexibility of the waist that we can move to adjust our aches to receive an incoming energy at the proper angle. Knowing how to move the waist to properly realign the arches is the understanding of peng-lu-ji-an.