An added advantage is the greater amount of speed and control which may be commanded in this way. The lax arm, being in a neutral state as regards motion, can be contracted in any desired direction without loss of force or of time, whereas a taut muscle cannot further effect motion of the arm without relaxation of its antagonistic muscles, which takes time.
Muscular Control
Considerable contral over one’s own muscles is necessary in order perfectly to relax arm and shoulder muscles just before the adjustment and then to utilize a measured and determined quantity of force in a desired direction. To acquire this much practice is necessary—practice on the living subject. The desired end may be hastened, however, by acquiring the abstract property of muscular control or by developing control already gained.
Many different forms of exercise will aid in the acquisition of muscular control and the ability to relax and then to follow the relaxation with an instantaneous whiplike contraction in a given direction. The best of these is without doubt bag-punching. The movements employed with a punching-bag, especially the lateral quadruple movement with both elbows and both hands, tend to develop precisely the sort of control needed for correct adjusting. The beginner can do no better than to practice in this way, by which, it must be remembered, only a necessary property, and not by any means the exact movement, may be acquired.
Amount of Force
The amount of force used in an adjustment varies so much in different spines and in different parts of the same spine that it is quite impossible to state any correct estimate of it in terms of physical units. In general the Cervicals move with least resistance, then the Dorsals, then the Lumbars, and finally the Sacrum and Ilia as hardest of all to displace or replace.
In developing additional force when it is found that the force first used on any vertebra has been insufficient to move it, remember this law: Work equals one-half Mass times the square of the Velocity. In other words, doubling the speed of the movement increases its effectiveness four-fold; tripling it, nine-fold.
The increase in force should never be effected by increasing the weight or pressure upon the patient’s body, for reasons which should be clear from a study of previous pages, but always by increasing the speed of the movement.
Names Used to Describe Movements
The names herein employed to indicate certain movements, each a well-defined method of procedure for the accomplishment of some special end, are the names or descriptive terms which seem to be in the most general use at this time. Few of these movements have arrived suddenly; most of them are the result of gradual growth and evolution: so with the terms by which they are known; they have gradually become a part of the common language of the profession. Usage sanctions them, though some of them are cumbersome, unwieldy, or entirely inappropriate.