In humans, muscles have a mixture of both aerobic and anaerobic
fibers. The aerobic muscles make up the foundation of the aerobic
system. These fibers account for the majority of muscle bulk in the
human body, more than 80 percent. This fact corresponds to the abil-
ity of humans to be better endurance animals than sprinters.
Aerobic muscles have two general functions: physical activity,
which helps us move and support our skeleton, and metabolic func-
tion, generating energy and other tasks. Aerobic muscle fibers physi-
cally get us through the day and they’re the ones we want working
during physical performance; they have the ability to work well for
long periods. They allow us to sit, type and walk throughout the day;
they protect the spine, hips and all other joints and bones. Without
good aerobic muscle function, we’re more vulnerable to joint prob-
lems, bone stress and other mechanical injuries.
Aerobic muscles thrive on physical activity. Without it, we can’t be
as healthy. Since most people are no longer naturally active, artificial
activity, otherwise known as exercise, is necessary. The intensity of
your exercise is a key factor, which I’ll discuss shortly. Briefly, aerobic
muscles are relatively slow-action muscles, capable of enduring easy
to moderate levels of activity for long periods of time. This means you
should be able to endure a long day’s work without getting exhaust-
ed, and still have energy to spare. They are well endowed with blood
vessels, so the more these muscles are used, the more blood flows
through them and the entire body. This improvement in circulation
brings more oxygen to all cells, and removes waste products, which
are always being produced. Conversely, the person who is very inac-
tive may have 70 percent of his or her blood vessels closed down!
The metabolic aspects of the aerobic muscle are the other key
components of the aerobic system. Within these fibers we produce
long-term energy through the conversion of fat in the muscle’s fat-
burning engines, the mitochondria. As fat-burning improves, the
body gets an unlimited supply of energy, and the fat deposits on your
hips, thighs, abdomen and even in your arteries can diminish. The
aerobic muscles also help antioxidants break down potentially dan-
gerous free radicals. Taking all the antioxidants you need won’t help
if your aerobic system is not working efficiently. The make-up of the
DEVELOPING MAXIMUM AEROBIC FUNCTION • 187