Suppose middle C is to be played with a force of eight ounces.
This force can be secured in many ways. I can drop my arm (the normal adult arm weighs from 6 to 15 lbs.) from a considerable height,
letting gravity accelerate the movement and increase its force.
This will be far in excess of what is needed. Accordingly, as the finger appoaches the key, I must inhibit the descent of the arm by contracting the forward abductors of the shoulder. If this inhibition be just the amount needed, the finger will reach the key with the desired force-effect of eight ounces. The movement as a whole will have been incoordinated, since there would have been an obvious waste of effort.
The inhibition of descent will have been a coordinated movement since the goal was reached.
If, in order to produce the same effect, I raise my arm for a part of the distance, sufficient , when it is dropped, just to produce the desired force effect, the entire movement will be coordinated, because there are no excess movements either in force or amplitude.
We are now in a position to understand the relationship between relaxation and coordination, which are by no means synonymous terms.
A coordinated movement necessitates the presence of just that degree of muscular relaxation that will transmit the desired force
to the desired point in the proper time. The degree of relaxation depends entirely upon the force required to produce the effect,
more rigidity or less than necessary will produce an incoordinated movement.
An incoordinated movement results from excess relaxation as well as excess contraction.
Too much relaxation (as in
locomotor ataxia[1]) may produce a movement just as inefficient
as that produced by too lit tle relaxation, as in paralysis of a musclenerve .