///// A G I N G ///// A G I N G \\\\\ A G I N G \\\\\ Part II /////

Aging-2

Age and Training Response

An appropriately graded aerobic training program can augment the aerobic power of 65 year old subjects by as much as 10 ml.kg-1.min- 1 over a 3 month period, effectively reducing the biological age of the oxygen transporting system by 20 years. A lack of aerobic power thus should not limit the independence of a well-trained, active individual unless she or he survives to the unlikely age of 100 years. Aerobic training eliminates premature disability, but has little influence on survival beyond the age of 80 years. Rather, it induces a "squaring" of morbidity and mortality curves, so that good health is preserved until shortly before death (4). Activity patterns in late middle age are quite strong predictors of the likelihood of dependency as a senior (11).

Because initial fitness is quite low, the aerobic condition of a senior can be improved by low intensity of training. Gains are greatest if a heart rate of 130-140 beats.min-1 can be sustained, but useful if slower progress is seen with regular training at heart rates of 110-120 beats.min-1 . In the frail elderly, heart rates rarely exceed 85 beats.min-1, and some training response may then be anticipated even with activities inducing a heart rate of only 100 beats.min-1.

Aging and Musculo-Skeletal Function

Aging leads to a progressive decrease of muscle strength and flexibility.

Muscles

Strength peaks around 25 years of age, plateaus through 35 or 40 years of age, and then shows an accelerating decline, with 25% loss of peak force by the age of 65 years. Muscle mass decreases, apparently with a selective loss in the cross-section if not the numbers of type II fibers. It is unclear whether there is a general hypotrophy of skeletal muscle, or a selective hypoplasia and degeneration of Type II fibers, associated with a loss of nerve terminal sprouting.

Other possible causes of functional loss include a deterioration of end-plate structures, impaired excitation-contract ion coupling, and decreased fiber recruitment. Both contraction time and half-relaxation time are prolonged, and maximal contraction velocity is decreased. Changes are greater in the legs than in the arms, possibly because there is a greater decrease in use of the legs with aging. Muscular endurance at a given fraction of maximal voluntary force apparently improves with age, in part because the muscles now contain a larger proportion of type I fibers and in part because weaker muscle contractions restrict perfusion less than in a younger person.

Loss of strength progressively impedes every day living. It becomes difficult to carry a 5 kg bag of groceries, to open a vial of medicine, and even to lift the body mass from a toilet seat (9). The male/female strength ratio is unchanged, so that women are limited by a loss of strength at an earlier age than men.

Muscle strength can be greatly improved by as little as 8 weeks of resisted training, even in 90 year old subjects (3). Protein synthesis proceeds more slowly than in a younger adult, but cross-sectional comparisons between active and inactive individuals suggest that much of the wasting of lean tissue can be avoided by regular resisted exercise. Stronger muscles further enhance function by stabilizing osteo-arthritic joints, reducing the risk of falls, and lessening the extent of dyspnea.

At one time, it was feared that resisted exercise might cause a dangerous rise of blood pressure, provoking a heart attack. However, if the subject avoids performing a Valsalva maneuver and individual contractions are held for no more than a few seconds at 60% of peak voluntary force, the rise of blood pressure is no greater than would be anticipated during a typical bout of cycle ergometer exercise.

Flexibility

The elasticity of tendons, ligaments and joint capsules is decreased as cross-linkages develop between adjacent fibrils of collagen. Over the span of working life, adults lose some 8-10 cm of lower-back and hip flexibility, as measured by the "sit-and- reach" test. The restriction in the range of movement at the major joints becomes yet more pronounced during retirement, and eventually, independence is threatened because the subject cannot climb into a car or a normal bath, ascend a small step, or complete the movements required for dressing and combing the hair.

Flexibility is thought to be conserved or improved by gently taking the main joints through their full range of motion each day. If muscle weakness and arthritis are already advanced, such activities are best attempted in warm water. Buoyancy then supports body-weight, and warmth increases the immediate flexibility of the joints.

Bone Structure

There is a progressive decrease in the calcium content and a deterioration in the organic matrix of the bones with aging. However, the dividing line between normality and pathology is unclear, and it is also uncertain how far a decrease of habitual physical activity contributes to the age-related calcium loss. Changes are more marked in women than in men, due in part to sex differences in the hormone profile and in part to a lower intake of calcium and good quality protein in women.

The calcium loss can begin as early as 30 years, and in women the process accelerates for some 5 years around the menopause. In later old age, the bones become so weak that a mild fall, a bout of coughing, or even a vigorous muscle contraction can cause a "pathological" fracture. A fracture of the hip quite commonly initiates irreversible bed rest and death. A deterioration of the vertebrae also contributes to senile kyphosis.

Regular load-bearing exercise can halt and sometimes even reverse bone mineral loss through the eighth decade of life. Such a regimen is particularly effective when accompanied by a high calcium diet (1500 mg/day). In women, many authorities also recommend the administration of estrogens, although the risks of such therapy require further assessment.

Aging and Metabolic Function

Many hormonal control mechanisms work less efficiently in an older person. For example, the pancreas and the thyroid are affected by damage to and/or a decrease in the number of secreting cells, and the ventricular muscle has a decrease in the number or the affinity of catecholamine receptors. Clinical consequences of these hormonal changes include the development of maturity-onset diabetes, and myxedema, with resulting obesity, poor cold tolerance and depression.

Diabetes mellitus presents immediate risks of ketosis, hyperglycemia and hypoglycemia. Long-term complications (skin infections, ulcers, peripheral vascular arteriosclerosis, myocardial ischemia, peripheral neuropathy, retinopathies and cataract formation) can also limit the subject's exercise tolerance. However, moderate exercise with some restriction of energy intake is an effective treatment for maturity-onset diabetes mellitus; many patients are thus spared the complication of long-term insulin therapy and rigid control of food intake. Exercise may also correct both obesity and depression in the patient with hypothyroidism.

Athletic Performance

The age of peak athletic performance depends upon the key functional element required of the successful competitor. In events where flexibility is paramount (for example, gymnastics and brief swimming events) the top competitors are commonly adolescents. In aerobic events, performance usually peaks in the mid-twenties, as gains from prolonged training, improved mechanical skills and competitive experience are negated by decreases in maximal oxygen intake and flexibility. Because of a longer plateauing of muscle strength, performance in anaerobic events declines less steeply, and in pursuits such as golf and equitation, where experience is paramount, the best competitors are aged 30-40 years.

Caution is needed in drawing physiological inferences from athletic records, since the pool of potential competitors decreases with age. Moreover, the motives of older participants often change from competitive success (winning at all costs) to social interaction, and some participants in Masters events lack cumulated skills, since they did not begin competing until they reached their late thirties.

Risks of Exercise

The risk of a cardiac emergency is increased substantially when a person is actually exercising. Some physicians have thus argued that older people who intend to exercise should undergo exhaustive preliminary screening, including an exercise electrocardiogram. This may be desirable if the person intends to embark on very strenuous competitive training, but it is undesirable if an older individual merely wishes to make a small increase in their habitual daily physical activity.

It is usually difficult to motivate older people to exercise regularly. Insistence on extensive screening suggests that physical activity is dangerous, and creates additional barriers of cost and time which reduce the likelihood that an intention to exercise will result in active exercise behavior. In fact, the interpretation of exercise ECGs is very difficult in many elderly persons, and there is little evidence that either a clinical evaluation or a stress electrocardiogram can detect those who will have an adverse exercise outcome. Moreover, the person who begins an exercise program is at a lower overall risk of sudden death than a sedentary peer, and perhaps because of a less ambitious attitude toward exercise, the relative risks of physical activity (deaths when exercising vs deaths when sedentary) decrease rather than increase as a person becomes older. Finally, if a well-loved form of exercise does provoke sudden death in an 80-year-old, this is a more pleasant end than many alternative ways of dying.

Nevertheless, certain precautions can increase the safety of exercise for the older individual. The recommended dose of exercise should do no more than leave the participant pleasantly tired on the following day. Recovery processes proceed slowly, and vigorous training should thus be pursued on alternate days. In individuals with pre-existing articular disease, walking should be substituted for jogging or running; fast walking offers an adequate training stimulus, with less risk of slipping, and a much smaller impact stress on the knees. Weight-supported activities such as swimming and aquabics are particularly helpful for those with joint problems. Vision, hearing and balance are all poorer than in a younger person. The senior should thus avoid sports where there is a risk of collision with opponents or stationary objects. If there is a history of falls, special care is needed in pursuing activities that require a good sense of balance (whether climbing, skiing and cycling, or merely walking on a slippery pool deck). In older people taking hypotensive medication, there is a danger of a sudden loss of consciousness when standing at the end of a bout of exercise, particularly if the room is hot, or the veins are relaxed by a period in a pool. Environmental extremes are poorly tolerated, and if the weather is extremely hot or cold, activity should be taken inside an air-conditioned facility (for example, rapid walking in an indoor shopping mall). For those who are extremely frail, some physical conditioning can be achieved using exercises taken from a sitting position.

Exercise training cannot restore tissue that has already been destroyed, but it can protect the individual against a number of the chronic diseases of old age. More importantly, it maximizes residual function. In some instances, biological age is reduced by as much as 20 years. Life expectancy is increased, partial and total disability are delayed, and there are major gains in quality-adjusted life expectancy. Exercise is thus a very important component of healthy living for the senior citizen.