What Are The Characteristics Of Muscle?

Muscles are among the things that set man and the animals apart from most plants in that they impart the ability to move. And not only do muscles enable us to get about on our feet and do many things with our hands, but many of the vital functions of our bodies depend largely upon our muscles. Breathing, the circulation of the blood, digestion, excretion and reproduction, all are dependent on our muscles, of which there are from five to six hundred or more.
Muscles account for 40 to 50 percent of the body's weight. They consist of about 75 percent water, 20 percent protein, 2 percent fat, as well as various kinds of minerals or salts. Individual muscles vary in length from about an eighth of an inch, in the inner ear, to eighteen or more inches, in the legs. Perhaps the tiniest muscles are those that cause our hair to stand on end when we are frightened or that give us goose pimples when we shiver from the cold.
Some muscles can lift a thousand times their own weight; some can exert a tension of forty pounds per square inch of their cross section. The muscle of a clam can keep a viselike grip for hours without apparently consuming any energy. The muscles of our hearts and our lungs work from the cradle to the grave without stopping. Some of our muscles can contract and relax in a fraction of a second. The muscles of certain insects are able to move or vibrate at fantastic rates—from 55 times a second in the case of some beetles, to as many as 1,046 times a second in the case of the midge, a tiny fly.