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Aging |
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Aging
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AgingWith each passing year, the composition of the population in America and probably many other "modern" societies is becoming older. This population increase of older citizens appears to be due, in part, to the large number of individuals of all ages who are experiencing modifications of lifestyle in a variety of ways including better working conditions, improved health/medical opportunities, and changing activity levels. Pollock et al (1) noted that the activity levels of elderly people has increased during the previous 20 years. However, it was estimated that only 10 percent of elderly individuals participate in regular vigorous physical activity and that 50 percent of the population who are 60 or more years of age described their lifestyles as "sedentary". Scientific studies and personal experiences continue to link many of the health problems and physical limitations found in the aged to lifestyle. Sedentary living appears to be a major contributor to the significantly adverse effect on health and physical well-being. Certainly there is increasing evidence indicating the vital need for improved national and international policies for better fitness, health, and sports for older individuals. In order to address some of these indicators, new attitudes and policies must emphasize activities and resources to meet the minimal requirements for keeping older people in good health, preventing their deterioration with age, and meeting the special interests of individuals with various disorders. In addition to the difficulties that hospitals, insurance companies, children of the elderly, and legislators face, the medical and scientific communities require time to determine the most appropriate solutions for improving the quality of these lengthening lives. Many of the myths about aging are being disproved while the true nature of age-related changes appears to be less bleak than previously thought. Increasingly, disuse and disease, not age alone, are revealed as culprits. There is an increasing awareness of the need for more emphasis on fitness to maintain wellness and prevent degenerative illness, for more research to understand the aging body of the healthy older person, and to determine the exercise needs of the ill and/or the handicapped. It is a fact of life that muscle tissue suffers some diminution from age. Age-associated changes in organ and tissue function such as a decline in fat-free mass, total body and intracellular water, and an increase in fat mass (2) may alter the physiological responses to exercise or influence the effect(s) of medication. However, in reality, any discussion about "age," realistically utilizes arbitrary time periods apportioned eons ago by men who evaluated time relative to the number of revolutions of the earth around the sun and the rotation of the earth on its own axis. These predetermined periods may or may not have any relationship with the aging of the cells in the body. The linkage between the chronological age and the biological age of people is imprecise. Perhaps a more accurate consideration of the relationship between chronological and biological age would be one that is non-linear, may differ with gender, or be dependent on other factors. It is an inevitable evolutionary consequence that individuals within a species differ in many ways. The characterization of an individual on the basis of a chronological age scale may be practical but biologically inappropriate. Function may have a greater influence on determining biological age rather than the number of times the earth has revolved around the sun. It appears that biological age can be affected by genetic code, nutrition and, most importantly, physical activity. Astrand (3) suggested that as an individual ages, the genetic code may have more of an effect on the function of systems with key importance in physical performance. He also noted that a change in lifestyle can definitely modify the "biological age", either upward or downward, at almost any chronological age. It has been suggested that the disparity of older persons is a hallmark of aging itself (4). It is important to determine how much age variance is due to the passage of time and how much is caused by the accumulation of other, non-time dependent, alterations. Previous attitudes towards physical adversities observed in the elderly were that they were attributable to disease. More recently, a third dimension associated with poor health in older persons has been described by Bortz (4) as "The Disuse Syndrome". For example, one of the most common markers of aging was thought to be a decreased lean body mass. However, analysis of 70-year-old weight lifters revealed no such decline. The components of the Disuse Syndrome has been similarly grouped by Kraus and Raab (5) in their book, "Hypokinetic Disease" and are:
Use is a universal characteristic of life. When any part of the body has little or no use, it declines structurally and functionally. The effects of disuse can be observed on any body part such as atrophied intestinal mucosa when a loop is excluded from digestive functions or the lung becomes atelectatic when not aerated. A lack of adequate conditioning and physical activity causes alterations in the heart and circulatory system, as well as the lungs, blood volume, and skeletal muscle (6,7,8,9). During prolonged bed rest, blood volume is reduced, heart size decreases, myocardial mass falls, blood pressure response to exercise increases, and physical performance capability is markedly reduced. On the other hand, although acute changes within the cardiovascular system result in response to increased skeletal muscle demands during exercise, there is evidence that chronic endurance exercise produces changes in the heart and circulation which are organic adaptations to the demands of chronic exercise (10,11,12,13,14,15). Cardiac performance undergoes direct and indirect age-associated changes. There is a reduction in contractility of the myocardium (16) and this increased stiffness impairs ventricular diastolic relaxation and increases end diastolic pressure (17). This suggests that exercise-induced increases in heart rate would be less well tolerated in older individuals than in younger populations. The decline in maximal heart rate is known and the cause is multifactorial, but is mostly related to a decrement in sympathetic nervous system response. Fifty percent of Americans who are more than 65 years of age have a diagnostically abnormal resting electrocardiogram (18). Another factor associated with aging is a progressive increase in rigidity of the aorta and peripheral arteries due to a loss of elastic fibers, increase in collagenous materials, and calcium deposits (19). When aortic rigidity increases, the pulse generated during systole is transmitted to the arterial tree relatively unchanged. Therefore, systolic hypertension predominates in elderly hypertensive patients. Other bodily systems demonstrate age-related alterations. Baraoreceptor sensitivity decrease with age and hypertension (20,21) such that rapid adjustment of the cerebral circulation to changes in posture may be impaired. Kidney functioning reveals a defect in renal concentrating ability and sluggish renal conservation of sodium intake causes elderly patients to be more susceptible to dehydration (22). Hyaline cartilage on the articulator surface of various joints shows degenerative changes and clinically represents the fundamental alteration in degenerative osteoarthritis (23). A decrease in bone mass (osteoporosis) can reduce body stature as well as predispose the individual to spontaneous fractures. Older women are more prone to osteoporosis than older men and may reflect hormonal differences (23). Older persons are less tolerant of high ambient temperatures than are younger people (24) due to a decrease in cardiovascular and hypothalamic function which compromises the heat dissipating mechanisms. Heat dissipation is further compromised by the decrease in fat-free mass, intracellular and total body water, and an increase in body fat. Unfortunately, the effects of disuse on the body manifest themselves slowly since humans normally have redundant organs which can compensate for ineffectiveness or disease. In addition, humans are opaque so that disease or deterioration are externally unobservable and, thus, go unheeded. For example, the early changes in bones due to osteoporosis are subclinical and are normally detected only after becoming so pronounced that fractures ensue. Cummings et al. (25) mentioned the difficulty of distinguishing manifestations in musculoskeletal changes due to disease from those related to aging. Muscle mass relative to total body mass begins decreasing in the fifth decade and becomes marked during the seventh decade of life. This change results in reduced muscular strength, endurance, size, as well as a reduction in the number of muscle fibers. Basmajian and de Luca (26) reported numerous alterations in the electrical signals associated with voluntary muscular contractions with advancing age. As yet, there are no findings yet published that have definitively located age-related musculoskeletal changes in either the nervous or the muscular system. The diaphragm and cardiac muscle do not seem to incur age changes. Perhaps this is due to constant use, i.e. exercise, or possibly a genetic survival mechanism. There is growing consensus that many illnesses are preventable by good health practices including physical exercise. Milliman and Robertson (27) reported that, of the 15,000 employees of a major computer company, the non-exercisers accounted for 30 percent more hospital stays than the exercisers. Lane et al (28) reported that regular runners had only two-thirds as many physician visits as community matched controls. The beneficial effect of exercise on diabetes has long been recognized and is generally recommended as an important component in the treatment of diabetes (29). Regular endurance exercise favorably alters coronary artery disease risk factors, including hypertension, triglyceride and high density lipoprotein cholesterol concentrations, glucose tolerance and obesity. In addition, regular exercise raises the angina threshold (30). Jokl (31) has suggested three axioms of gerontology:
The health in older people is best measured in terms of function, mental status, mobility, continence, and a range of activities of daily living. Preventive strategies appear to be able to forestall the onset of disease. Whether exercise can prevent the development of atherosclerosis, delay the occurrence of coronary artery disease, or prevent the evolution of hypertension is at present debatable. But moderate endurance exercise significantly decreases cardiovascular mortality (32). Endurance exercise can alter the contributions of stress, sedentary lifestyle, obesity, and diabetes to the development of coronary artery disease (33). Consider, for example, the four-time Olympic discus champion, Al Oerter. At the age of 43, he focused his training to qualify for the 1980 Olympic Games which would have been his 5th consecutive Olympiad. Al Oerter threw his longest throw -- 220 feet -- but, since the U.S. boycotted the 1980 Moscow Olympic Games, his chance was denied. By the time of the 1984 Los Angeles Games, Al was forty-seven years old. Even at an age well beyond most Olympic competitors, he again threw his best, exceeding 240 feet in practice sessions. Al's physique and strength suggested that his biological age was less than his chronological age. Biologically, he was probably between 25 and 30, although chronologically he was 15 to 20 years older. Unfortunately in the competition that determined which athletes would represent the United States, Al suffered an injury which precluded him from trying to achieve an unprecedented fifth consecutive Olympic Gold medal. Read more of this article
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