Symmetry and asymmetry
When we look at man, we normally see two arms, two legs, a head in the middle, as well as the nose, two eyes, and so on. There appears to be a pronounced (left-right mirror) symmetry. Symmetry is found beautiful and attractive. Various theories and therapies assume a symmetrical structure of the human body. Yet something strange is going on here. An explanation.
The adaptability of man
An important feature of man is that he/she can adapt. Stimuli given to the living body initiate change processes so that the body can process these stimuli better the next time. Example: when I regularly hop on my right leg, my right calf muscle will develop in strength and the Achilles tendon in strength. But my left calf muscle and Achilles tendon remain as before. In the living body all tissues can adapt: muscle, tendon, cartilage, bone, and so on. The speed of adjustment differs per type of tissue.
The role of behavior
People can be recognized by their behavior, including how they move. This movement behavior is typical per person. It is subject to little change if the person is not disturbed by, for example, pain or a fracture. The body thus continuously receives the same stimuli for change, for example when walking. This way the body will adjust itself until it has optimally formed to be able to carry out this movement behavior efficiently. Because movement behavior is asymmetrical behavior, the body will form asymmetrically.
Asymmetric behavior? When I walk from A to B, do I use left and right equally? Answer: maybe, but the way I use my left and right leg is different. Examples: the left and right pass can be different in length, with the one foot I walk slightly more outwards than with the other, with the one arm I swing more than with the other, and so on. Take a look at the wear patterns of the shoe soles: these are seldom equal to the left and right.
Effects
For example, the consequences of the asymmetrical adjustments in the body translate into: unequal leg length, one shoulder is higher than the other, the nose is slightly crooked, the construction of the first cervical vertebra (atlas) is different on the left-right. Note: this concerns normal (so-called functional) adjustments and not errors.
This has consequences for the physical examination and its interpretation. In the first place, it is possible to predict on the basis of behavioral tests how the body has developed asymmetrically, for example which leg will be longer. Secondly, it can be predicted how a joint (for example left hip compared to the right) will move asymmetrically. This way the head/neck can also turn one side further than the other. In the third place, this may mean that symmetry in the form or in the movement can actually be deviant .... The starting point that the human body is symmetrical in form and function is not sustainable. A phenomenon that must be taken into account in practice.
See also the articles about preferential movements and mass mechanics, and orthomanipulation.