The Truth About Aging

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 shrink.
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 mass.

Bone mass. Bone mass typically increases by radial growth until about age 30, after which there is plateau, and
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 stronger.

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 itself.
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.


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