How Action Of The Muscle Resembles That Of Machine
( Originally Published 1936 )
As you stand on a beautiful afternoon such as this, with a long stick in your hand, gazing down at a golf ball, or with a baseball in your hand about to throw it towards the waiting catcher, the actions which you perform are basically those of an extremely efficient ma-chine.
The efficient machine is a muscle bundle. Of course, in any complicated action a good many muscle fibers are called into play. A muscle fibril is essentially a string of plasma which would appear as alternate discs of light and dark colored material. In any muscle, these fibrils are bound into bundles so that in the main muscle of the upper arm there are several billion muscle fibrils. When the arm is bent, each of these fibrils contracts, bending the forearm on the upper arm by the movement of the elbow joint.
When, as a result of this contraction, the golf ball rises from the ground and moves upward in the air away from the earth, it does not, as some people say, "defy gravity." It has simply responded to the release of energy in the arm muscle. That energy is released because the muscle is able to convert one kind of energy into another kind.
Very largely this conversion of energy is of a chemical nature. The muscle is a machine which converts sugar into mechanical energy by burnin just as the gasoline motor converts gasoline-in o mechanical energy This is easily proved by sending a sugar solution through a muscle which is undergoing a series of contractions. At the time that the muscle begins to contract, the amount of sugar in the solution lessens and the longer the contraction occurs, the more sugar is used up.
This knowledge of the muscle as a machine using sugar for fuel is a rather recent development, and for a complete elucidation of it the Berlin physiologist, Meyerhoff, received the Nobel prize.
The remarkable thing about the muscle as a machine is that it is possible during one of its phases to burn sugar without utilizing oxygen. It cannot, however, keep this up very long and, as a matter of fact, muscle fatigue is simply due to the fact that the heart cannot pump blood containing oxygen to the muscle fast enough to keep it going. If it were possible to supply a muscle with oxygen indefinitely, that muscle could probably keep on doing work indefinitely.