Physiological Benefits of Exercise - Exercise
Physiological Benefits of Exercise
Professional athletes, marathon runners, or people who exercise regularly tend to look healthier than those who do not exercise. Their bodies are slim, their muscles are firm, and they have more energy. Physiologists have long been struck by the similarities between the effects of sedentary living and aging, so much so that many researchers have concluded that many of the “normal symptoms of aging” may be, in part, symptoms of inactivity. Such effects include changes in the cardiovascular and respiratory system, cholesterol levels, bone mineral mass, joint flexibility, bowel function, immune system function, sleep patterns, sensory abilities, and intellectual capacity.
Exercise Helps Maintain Heart and Lung Fitness. The most important physiological benefit of exercise is that it helps maintain heart and lung fitness. The heart's function is to pump blood (most adults have slightly more than a gallon of blood in their bodies) through more than 60,000 miles of blood vessels. Each day the heart beats approximately 100,000 times, depending on the body's activity. In a 70-year lifetime, an average human heart beats more than 2.5 billion times. The respiratory system, including the lungs, provides the body with oxygen and removes carbon dioxide via tiny air sacs in the lungs called alveoli (which number approximately 300 million).
The heart's ability to pump blood drops an average of 58% between the ages of 25 and 85. By age 70, lung capacity can decrease by 40–50% and muscle strength by 20%. In fact, scientists now think that by the time most people turn 20, their cardiovascular and respiratory functions have already begun to decline, a trend that accelerates throughout life. As the heart becomes less efficient with age, oxygen is thus delivered to the muscles more slowly. Exercise increases the size of the heart muscle and its chamber volume, and greatly improves its efficiency.
Exercise Lowers Hypertension (High Blood Pressure). Diastolic blood pressure rises with age by as much as 10% between the ages of 60 and 70. Poor nutrition, a sedentary lifestyle, and an increasing intake of medications generally combine to increase blood pressure in the elderly. As a result, the heart has to pump harder than normal because of an excess of fluid in the bloodstream combined with narrowed or constricted arteries. Both the pumping of the heart and the functioning of the arteries affect blood pressure.
Along with stress reduction therapies such as yoga, meditation, hypnosis, and biofeedback, regular sustained exercise effectively lowers blood pressure. People with hypertension should consult their physician before starting any form of exercise because even mild exercise temporarily raises blood pressure. The best exercises, according to clinical trials, are those that reduce the level of stress hormones in the bloodstream that constrict the arteries and veins. Progressive weight lifting, walking or jogging three times a week for 20 minutes, stationary bicycling, and a combination of walking, jogging, and bike riding have all been found to lower blood pressure.
Exercise Prevents Loss of Muscle Mass. As people age, they can lose as much as 10–12% of their muscle mass with no appreciable loss in overall body weight. In fact, they normally gain weight. Men in their 80s can lose another 20 pounds of muscle mass, while continuing to gain body fat.
A 1990 Tufts University study cited in The Exercise Bible: The Medical Benefits Of Exercise showed that working out can build muscle mass in elderly people. Ten nursing home residents at the Hebrew Rehabilitation Center for the Aged in Boston, between the ages of 87 and 96, completed two months of high-intensity resistance training using weights. The participants nearly doubled their leg muscle strength, increased thigh muscle size by 9% and improved performance on mobility tests. The researchers concluded that strength training effectively helps people of advanced age with multiple chronic diseases, functional disabilities, and nutritional inadequacies build muscle mass.
Exercise Reduces Body Fat and Helps Maintains Ideal Body Weight. The benefits of exercise in helping people lose weight or maintain their ideal body weight have been extensively documented in many studies. Exercise burns calories consumed as food, and raises the basal metabolic rate (BMR). In order for an individual to lose weight, energy intake must be less than energy expenditure. This can be done by decreasing calorie intake (dieting) or by increasing the rate at which the calories are burned (exercising). To lose one pound, people must consume 3,500 fewer calories than they expend in a typical week–or 500 calories per day. Most individuals will begin to lose weight if they decrease their calorie intake below 1,500 calories per day and engage in aerobic exercise for 15–20 minutes three to four times per week.
Exercises to Lose Weight
The following forms of exercise have been shown to burn a significant number of calories in only a 30-minute period. The figures are calculated for a 130-pound woman.
|Aerobic Exercise (intense)||Calories Expended|
|Cross-country skiing (walking speed)||252|
|Cycling (9.4 mph)||177|
|Golf, pulling cart||300|
|Handball or squash||660|
|Ice or roller skating||400|
|Jogging (5 mph)||480|
|Running (8-minute mile)||375|
|Stair climbing (moderate pace)||285|
|Step aerobics (6-inch step)||175|
|Step aerobics (8-inch step)||208|
|Strength training (free weights)||150|
|Walking (on pavement)||141|
|Walking (treadmill at 3 mph)||132|
|Walking (2 mph)||120–150|
Physical energy expenditure (PEE) has the greatest impact of any other variable on total caloric requirements. Whereas the average sedentary person usually expends only 300–800 calories a day in physical activity, athletes in training or workers engaged in heavy manual labor may expend as many as 3,000 calories.
Exercise Improves Glucose Tolerance and Reduces Insulin Resistance. Exercise not only helps control weight gain, but it also plays an important role in improving glucose tolerance and reducing insulin resistance–both significant factors in the development of diabetes. Glucose tolerance is a measure of the body's ability to metabolize glucose as it is released into the bloodstream. This ability usually declines with age. Since insulin's ability to convert glucose in the cells is also reduced, glucose can gradually increase to dangerous levels in the bloodstream.
Increased muscle activity, however, accelerates the transport of glucose into muscle cells regardless of the presence of insulin, thereby helping to compensate for insulin resistance. Consequently, exercise can sometimes be a useful tool for controlling type II diabetes and may even help prevent it in some cases. It may also forestall the serious complications of the disease.
Exercise Helps Maintain Bone Mass and Prevent Bone Loss. Bone is constantly being formed and reabsorbed throughout a person's life. Until the age of 35, more bone is deposited than removed, leading to a net gain in bulk and strength. After 35, however, the trend gradually begins to reverse.
According to the June 1994 Tufts University Diet & Nutrition Letter , 24 million Americans, 80% of them women, suffer from osteoporosis, a progressive condition in which bones lose mass and become extremely brittle and prone to injury. Osteoporosis begins when the body cannot make new bone fast enough to replace bone loss. Both men and women lose some bone mass as they age, but the rate of loss is much slower in men (who have denser bones to begin with) than in women, and osteoporosis is rarely a problem for men. Conversely, according to Kurt Butler and Lynn Rayner, women who live to the age of 80 usually lose a third to two-thirds of their entire skeletons and up to six inches of their height.
The process of bone loss typically begins in a woman's mid-30s, some 10–15 years before the onset of menopause, at a rate of 0.5–1% a year. This loss increases to 2–5% in the first 10 years following menopause, and then tapers off to about 1% per year. In the decade after menopause, women typically lose 5–10% of the bone-sustaining minerals in their spines alone. As a result, according to the National Osteoporosis Foundation, one-third of American women over 65 suffer spinal fractures and 15% break their hips because of osteoporosis.
Exercise appears to stimulate bone mineralization. Even though women who exercise regularly tend to have lower estrogen levels and be thinner (two states associated with higher risk for osteoporosis), the effect of exercise more than compensates for those factors, giving these women denser and stronger bones than women who do not exercise regularly. A study at the Queen Elizabeth Hospital in Toronto, Ontario, compared bone densities of sedentary women between the ages of 50 and 62 with those of women who engaged in aerobic exercise and others who did both aerobic and strengthening exercises. The active women of both groups experienced similar significant gains in bone mass, while the sedentary women showed a loss.
After puberty, the only way women can increase their bone mass is to continually exercise. It is still unclear whether women in their 70s can significantly increase their bone mass. It also appears that those bones most directly stressed by exercise increase in size the most. Nancy Lane, a rheumatologist at the University of California in San Francisco, has extensively researched the bone density of older female runners. She suggests that exercise can slow the rate of bone loss during menopause, while the benefits from gains in strength and balance help to prevent falls.
A study at Washington University School of Medicine in St. Louis suggests that lifting weights is the best way to build bone mass. The Bone Mineral Mass (BMM) was significantly higher for those participating in a weight-bearing program (more than six hours per week of rigorous weight lifting) combined with aerobic exercise (more than 40 miles per week of running or more than six hours per week of aerobic dance classes) than for sedentary people or people participating only in aerobic exercise. Other studies have shown that competitive master swimmers have greater bone mineral content than non-athletes.
Exercise Helps Maintain Joint Flexibility. Joint flexibility is also a special concern of the elderly because the aging process gradually diminishes the amount of fluid in the joints. Rheumatoid arthritis, the most common disorder of the joints, is caused by inflammation of the lining of the synovial capsule (the fiber tissue surrounding bones and cartilage). Exercises for rheumatoid arthritis sufferers help maintain cartilage, mineralize underlying bone, strengthen shock-absorbing muscles and ligaments around joints, and increase joint flexibility. Several new programs at the University of Michigan Medical Center, for example, suggest that weight lifting in water helps distribute synovial fluid around the cartilage and throughout entire joint spaces.
Exercise Reduces Depression and Negative Moods. With aging, a reduced cerebral blood flow causes a depletion of neurotransmitters (biochemicals in the brain that send instructions from neuron to neuron), which may affect memory, attention span, concentration, and learning function. The neurotransmitters norepinephrine, serotonin, and dopamine require oxygen for their synthesis and metabolism, and regular endurance exercise is an excellent way to supply this oxygen to the brain.
Depression is linked to disturbances in these neurotransmitter levels–a major reason why aerobic exercise is now being prescribed for depressed patients. The mood improvement experienced after vigorous exercise may also be related to a better biochemical balance in the brain.
Exercises which require the least expenditure of energy produce the least amount of change on depression and mood levels. Any exercise to lower depression must be progressive because people who start with high intensity workouts are most likely to quit and therefore will not realize the benefits of exercise.
Exercise Helps Increase Life Expectancy. Can regular exercise lengthen life expectancy? Dr. Ralph Paffenbarger's study of 1,700 Harvard alumni whose weekly energy output in walking, stairclimbing, and active sports totaled at least 2,000 calories had a 28% reduction in all-cause death rates. For those expending 3,500 calories a week in exercise, death rates were an astonishing 50% lower. Life expectancy was 2.15 years greater for those who expended more than 2,000 calories than for those who expended less. In practical terms, because even sedentary people burn 1,000 calories a week in physical activity, this improvement in longevity can be gained by walking or jogging 8–10 miles a week. In general, regular physical activity has a beneficial impact on life expectancy by reducing the likelihood of chronic diseases such as heart disease, obesity, and diabetes. However, there is no evidence to support the contention that physical activity can actually lengthen lifespan (the maximal obtainable age of a particular person).
The physiological benefits of exercise are perhaps most evident in coronary artery disease (CAD). Hypertension (high blood pressure) is considered a major risk factor for CAD and is less likely to develop in people who are physically fit. Exercise, whether it is accompanied by weight loss, also raises the body's production of high-density lipoprotein (HDL), an effect associated with a lower risk of CAD. Both elderly and young men appear to exhibit similar HDL rises, with the degree of benefit apparently commensurate with the intensity of exercise. Even brisk walking for 2.5–4 hours per week, however, is sufficient to raise HDL levels. HDL is especially important to men over 50, for whom it is the single most important cardiac risk factor.
In Paffenbarger's long-term study of the health and lifestyles of approximately 17,000 male Harvard alumni between the ages of 35 and 74, those who exercised relatively strenuously for 4.5–8 hours per week reduced their chances of coronary disease by approximately 50%.
Exercise Reduces Back Pains. Back pain is almost always associated with muscular weakness. Regardless of whether this weakness is a cause or an effect of pain, exercise can usually produce increased strength and function of the back muscles and decrease pain. Dr. Richard A. Deyo, Professor of Medicine and Health Services at the University of Washington School of Medicine, uses exercise to reduce the number of days back-pain patients spend in the hospital. According to an article by Joel Posner in the March 15, 1992 issue of Patient Care , Deyo prescribes a minimum bed rest period for back-pain patients, normally no more than two days if necessary (most doctors recommend two weeks in bed). Dr. Deyo suggests that prolonged bed rest may increase later back pains because it contributes to bone loss, general weakness, and blood clots in the legs. Light weight lifting, preferably with hydrotherapy; swimming; rowing machines; stretching; and yoga have all been found to be effective in relieving back pain.