Gravity is the only constant environmental stimulus that effects the nerve receptors in your muscles and joints. Under normal conditions the nerve receptors in your muscles and joints can adapt to the change created by gravity. Change created by sudden or repetitive trauma will reduce your body's ability to respond to the effects of gravity. Trauma also creates changes in the ability of your body's joints to move properly. There are many different types of trauma.
Obvious trauma is that which is associated with impact such as auto and sports injuries.
Lesser trauma examples are improper lifting techniques, repetitive movements or poor posture. Chiropractic is not drugs or surgery. It is a hands on method of treatment to cause a change in function of mechanoreceptors in the involved joints to effect the nervous system. Recent studies in neuroanatomy confirm that mechanoreceptors have a direct effect on brain function. Genetically we are all different.