The Truth About Aging
- BY PETER BRUNO, M.D
Time waits for no man. But the passage of time does
not mean decline - not necessarily.
Many physiological changes come with age. Some of .these
changes can be attributed to natural processes that
take place in the body, others to external factors.
Over time, for example, cells gradually and steadily
deteriorate, becoming less proficient at self-repair
and replication. But, people also tend to exercise less
as they get older, and this disuse may have more to
do with the aging process than has been traditionally
believed. In fact, recent studies of senior athletes
have prompted physicians to redefine the physiology
of aging as the physiology of disuse. These physiological
changes can be better understood when they are broken
down into categories.
Cardiovascular capacity. The function of the heart
muscle and the peripheral vascular system change with
age and decreased physical activity. Stroke volume-the
amount of blood pumped out of the heart with each beat-falls
approximately 30 percent Over a lifetime, and the heart
enlarges. As a result, resting cardiac output is reduced
by 58 percent. Lung compliance increases, the chest
wall becomes stiffer and less mobile, and the maximum
amount of air that can fill the lungs decreases by 40
to 50 percent by age 70. To compensate, the heart must
work at a 20 percent higher rate. A program of vigorous
physical activity can boost the power of the lungs,
the heart and I the body's blood vessel network, so
that a maximum amount of oxygen can be taken in, which
then can be processed processed efficiently for use
by the muscles.
Reaction time. From a person's peak, nerve conduction
velocity slows 10 percent to 15 percent until age 60.
So when an older tennis player sees a ball coming, t
he's going to take 10 percent longer to react. The time
is short, but it's perceptible. Someone who has played
many years, however, knows how to anticipate and can
react automatically. What an older play loses in reaction
time, he can make up with experience.
Muscle mass. Most people, as they move from young adulthood
into middle age, lose between six and seven Pounds of
muscle, or lean body mass, every decade. This adds up
to a loss of almost 30 percent of the total number of
muscle cells between the ages of 20 and 70. What's more,
the muscle cells that , remain begin to atrophy, or
The result is that muscles can't contract with as much
force and so exert diminished strength. A decline in
the number of muscle cells is inevitable, but a decline
in the size and strength of . the muscle cells that
remain is not. Many studies now indicate that exercise
can not only slow but reverse the decrease in muscle
Bone mass. Bone mass typically increases by radial
growth until about age 30, after which there is plateau,
then a decline. Regular workouts, however, help maintain
bone density and thereby J ward off osteoporosis. Free
weight Nautilus machines, walking and running are key
exercises. Apparently, the stress that gravity exerts
during such activities helps bones maintain their mineral
content. Rather than weakening bones, repeated stress
causes them to stay strong-and in some cases become
Metabolism. Metabolism slows, and the basal metabolic
rate-the rate at which the body expends calories while
at rest in order to carry out such functions as breathing
and cell division-decreases at an estimated two percent
every 10 years, starting at age 20. So with each passing
decade, 100 fewer calories are needed per day. At the
same time, -relative body fat increases with age. Regular
exercise helps compensate for the natural decline in
the basal metabolic rate. The built-up muscle cells
created by exercise counteract the need to reduce calories.
This is because muscle, as opposed to fat, is relatively
active tissue requiring extra caloric fuel to maintain
Protection against chronic disease. Regular exercise
also helps reduce risk for coronary heart disease by
directly affecting risk factors for the disease. For
example, routine physical activity helps prevent clogged
arteries by decreasing blood pressure and elevates the
amount of high density lipoprotein, or HDL, the "good"
cholesterol. Although doctors have always recommended
lowering total blood cholesterol to thwart heart disease,
many now believe that an elevated HDL, combined with
a reduced-fat diet to lower bad LDL cholesterol, offers
an even better chance of staving off heart attacks.
It is impossible to avoid growing older. But it is possible
through exercise to slow down physiological changes.
A study of 17,000 Harvard alumni found that those who
lived longer and had the highest quality of life were
not the ones who had been athletes at Harvard but the
ones who exercised regularly after college.