When you are at rest all the muscles of the
body use only about one thirtieth of the oxygen they can use during maximum
effort. With a well-rounded exercise program, they can be made to use much
more. When they do, the heart will respond, pumping harder to get more
oxygen-carrying blood into circulation, and over a period of time, heart
pumping efficiency will increase; the heart will pump more blood with each
stroke. At the same time, lung capacity-much of it never used in sedentary
living-will enlarge to absorb and feed more oxygen into the blood- stream. The
higher oxygen content will aid muscle as circulation improves in both quality
and body; the capillaries penetrating into muscles will open and become more
effective.
A good exercise program also will help to
strengthen the muscles around the veins in the lower part of the body, and this
is of considerable importance. When you stand, the veins in the legs expand and
there may be a tendency for them to become distended with blood which pools in
them 50 that less blood is available for circulation through the rest of the
body. As less blood returns to the heart from the veins in the lower part of
the body, the heart, with less blood to eject with each beat, tries to
compensate by increasing its beat rate. But this is not always effective and
does impose added stress on the heart. The amount of blood that can pool in the
lower veins depends considerably on the amount of pressure by the muscle
tissues around the veins. If the tissues are tight and firm, the expansion of
the veins is limited.
Soft muscles without tone do not provide
much external support to the veins to prevent their expansion. Thus, a good
program of exercise can have many admirable effects throughout the body-in
terms of health of heart, lungs, muscles, blood vessels. We suggest that you
read, in connection with this discussion, the contents of Chapter 8 on
exercise.
A word here about nutrition; It, too, is
vital in the proper care of muscles. A good diet containing the sources of
protein described in Chapter 6 will help you build and maintain strong, healthy
muscles.
