THE MUSCLES BONES
FORM the framework; joints
permit movement; and it is the muscles that do the moving when they pull on
bones. The hundreds of voluntary muscles in the body weigh two and one-half
times as much as all the bones together. They constitute the flesh that gives
the body its basic shape. An understanding of muscles and how they function is
very much worth having, since it can help you to use your muscles most
effectively, prevent injuries to them, and prevent progressive deterioration if
an injury should occur. As noted in the preceding chapter, good muscle tone is
an important element in preventing skeletal problems, and as we will point out
in this chapter, tone is also important in maintaining good circulatory
function. Muscles always work by pulling, never by pushing.
Muscle fibers contract and as they do so
the muscle pulls a bone toward it. The body is so engineered that where one
muscle acts to pull a bone in one direction, there is another muscle that can
be contracted to pull the bone in the opposite direction. Thus, for example,
the bulge that can be felt in the front of the upper arm when the lower arm is
drawn up is the body of the biceps muscle. The mate to the biceps, called the
triceps, lies on the opposite side of the arm and when this muscle contracts it
straightens the elbow and stretches the biceps into position for another
contraction.
Muscle
tissue is formed before birth, and a baby's supply of muscle fibers is his
supply for life. The fibers, of course, grow as the child grows. Strength
develops as the fibers do their work of contracting. The arms of a blacksmith,
prizefighter, or weightlifter contain about the same number of fibers as do
those of a little girl but are much stronger and thicker through use.
