Keeping Fit - Physical changes
P hysically, middle age should be a pleasant plateau—a time to look back on a vigorous youth, enjoy an active present, and prepare for a ripe old age.
Middle age should not be measured by chronological age but by biological age, the condition of various parts of the body. You might say that the middle-aged body is like a car that has been driven a certain number of miles. It should be well broken in and running smoothly, but with plenty of reserve power for emergencies, and lots of mileage left.
Biological age should be measured by the state of the heart, arteries, and other essential organs, the length of life and comparative health of parents and grandparents, temperament and outlook on life, and outward appearance. The way you have fed or treated yourself is important. Eating the wrong kinds of food, being overweight, smoking too much, or worrying too much can add years to biological age.
However, no one should be surprised if he is not in quite the shape he was when he was 25 or 30 years old. At age 40 to 50 it is perfectly normal to have only 80 percent of the maximum breathing capacity, 85 percent of the resting cardiac output, 95 percent of the total body water, and 96 percent of the basal metabolic rate. These factors, however, should not slow anyone down very much.
There is one difference, though, that can be anticipated in middle age. Reaction time and decision-making processes may be a bit slower. This is because the nervous system is one of the most vulnerable to aging. The cells of the central nervous system begin to die early in life and are not replaced, while other organs are still growing and producing new cells. Specific response to input is delayed because it takes a greater length of time for an impulse to travel across the connections linking nerve fibers.
Thus, though you may function as usual under normal conditions, you may find it a little harder to respond to physical or emotional stress. However, if you have followed a sound health maintenance program, including good nutrition, enough mental and physical exercise and rest, and moderate living habits, you should respond to unusual physiological or emotional stress quite adequately.