America is growing older at a rapid pace. In 1900, 123,000 people were age 65 or older. It was projected that in 1990, however, there would be 32 million people in that age category.1 The result of the increased life expectancy is an increased duration of morbidity ("a period of time preceding death in which an individual is permanently ill or infirm" 1X which increases healthcare costs. It was projected that the health-care costs for the institutionalized elderly alone would be $75 billion in 1990.1 One means of controlling health-care costs while improving quality of life is to keep the aging population as healthy as possible.
Interventions that slow die decline in functional capacity (0.75% to 1 .0% per year after the age of 302) can help improve personal health, enhance enjoyment of Ufe, and improve productivity. Research has found that decline hi aging can be altered by physical activity.3,4 Therefore, exercise is considered an intervention that will help maintain and enhance functional ability as chronological age increases.3
Literature that supports die value of exercise as a positive intervention in the aging process was reviewed and categorized by selected body systems (Rgure 1). The systems included are the circulatory system (cardiovascular and blood components), the musculoskeletal system (muscles, bony structure, and body composition), and the regulatory system (metabolic and nervous system).
Maximal Oxygen Consumption
Maximal oxygen consumption (VO2 max) is the best measure of how efficiently the cardiovascular system transports oxygen to the tissues.3 Studies have consistently revealed that VO2 max decreases with age, but the decline can be slowed by consistent physical activity.5,6 The reduction in VO2 max begins at about age 25 and continues to slowly decrease until age 6S.6*8 For healthy, untrained men, the average decune in VO2 max is 5% to 10% per decade.6 Heath et al6 reported that age, combined with a decrease in exercise and an increase hi body fat, resulted in a drop in VO2 max of approximately 9% per decade. The aging process per se, with weight and exercise held constant, resulted in a 5% decune per decade.6
Although exercise training cannot eliminate the age-related decline, it has been shown that older athletes (59 ±6 years) have a 60% higher VO, max than untrained men of similar age* It should be emphasized that high intensity exercise is not a prerequisite for improvement of VO2 max for elderly populations.8 A 6-month walking program (heart rate less than 120 beats per minute), for example, increased the VO2 max an average of 12% (range 1% to 42%) whereas high intensity exercise (75% heart rate reserve) increased VO2 max 18% (range 1% to 39%) in subjects 63 ± 2 years old.8 Therefore, an exercise program can be designed to increase or maintain oxygen intake without the demands and dangers of an exhaustive workout.
An age-related decline in maximal heart rate has also been substantiated by many researchers.5'6,9 This decline affects the oxygen consumption rate, cardiac output (COX and stroke volume (SV). The age-related CO decline is demonstrated at rest as well as during exercise.4 In older persons, the lower CO during exercise is augmented by increases in heart rate and SV, whereas younger subjects show only an increase in heart rate.10 In other words, the heart has to work harder to maintain CO in older individuals.
When compared with young runners, older athletes (age 56 ± 5 years) demonstrated a 15% to 20% higher systemic vascular resistance.5 This difference in vascular resistance may be partially responsible for the age-related increase in blood pressure.5 Studies have shown that endurance training can significantly reduce the mean blood pressure and the systemic vascular resistance in older individuals.8
Serum lipids and lipoproteins are important blood components due to their association with coronary heart disease and atherosclerosis. Higher levels of total cholesterol and triglycérides are seen with aging; however, the effects of age on low density lipoprotein (LDL) and high density lipoprotein (HDL) are not as clear.4,11 Fitzgerald reported that HDL is unchanged with age and LDL increases with age.4 In contrast, Tran et al found that LDL was not correlated with age but that HDL decreased with age.11
Several studies have shown that exercise decreases the triglycéride levels and increases the HDL levels for middle-aged and older persons.11"13 However, the decrease in triglycéride levels is only maintained for approximately 42 hours before returning to pretraining levels.13 Therefore, physical activity at least every other day is essential. In addition to a consistent physical activity regimen, an exercise intensity of at least 60% of maximal heart rate is essential to attain a positive effect on lipid and lipoprotein blood levels.1 1,12
The immune system is involved with a variety of disease processes ranging from the common cold to rheumatoid arthritis and acquired immune deficiency syndrome. The immune system also manifests age-related impairment. Some of these impairments include hypogammaglobulinemia, a decrease in response to antigens, and an inadequate number or impaired functioning of T cells.14 Although it is known that immune functions deteriorate greatly with age, the exact mechanisms are unclear. Therefore, a treatment to slow the deterioration of the immune responses as a person grows older is also unknown.
Some people who exercise believe they have fewer infections.15 Whether exercise improves the immune system, however, is still open to question. Several investigators have found an increase in white blood cells or granulocytes after exercise or training. l6 However, others have found no change or even a decrease in white blood cells.15,16 Therefore, further study is necessary to reveal what factors may benefit the immune system as one ages.
EFFECTS OF EXERCISE AND AGING ON SELECT BODY SYSTEMS
Muscle Strength and Endurance
Muscular strength begins to decline around the age of 40 with an accelerated decline after the age of 60. 17 Changes in lifestyle or the decreased use of the neuromuscular system are the primary causes of this muscular strength loss.18 Physical training has been shown to improve muscle strength as well as slow its decline.2'17,19 Pavlou et al studied the effect of exercise on the muscular strength of middle-aged men and found a significant (22%) increase in muscle strength.19 These findings have been verified by Laerum and Laerum17 and Landin et al.2
Short-term muscle power has been shown to be affected by muscle temperature. Davies and Young20 found that for older men, the peak power output in a vertical jump was increased by 20% with an increased muscle temperature. The authors concluded that heating a muscle before use changes the capacity of the muscle to generate power. Heating the muscles of a client via a warm bath or whirlpool may improve the muscle power and thereby improve the chances that the client can carry out activities of daily living with greater ease.
Skeletal muscle endurance does not follow the age-related decline as seen with muscle strength.21 The maintenance of skeletal muscle endurance may be due to the decline in fest-twitch muscle fibers with little change in slow-twitch muscle fibers.21 Fasttwitch fibers are associated with lactate accumulation which, hi turn, decreases muscle endurance.21 Therefore, because the elderly have proportionately fewer fast-twitch muscle fibers, the endurance of the muscle may not change due to a decreased lactate accumulation during dynamic exercise.21
Another important aspect of mobility is flexibility. Physical training has been reported to decrease the age-related decline in flexibility.2'4,17,18 However, Walker et al found no significant difference in joint movement between older subjects with high and low leisure-time activity levels.22 These findings indicate that an exercise-related increase Ui flexibility cannot be assumed.
The major age-related skeletal system change is osteoporosis, in which both the matrix and mineral content of the bone deteriorate.2,3 Osteoporosis begins at an early age and occurs four urnes more frequently in women than in men. The bone loss begins in women around 30 to 35 years of age with a steady decrease of 0.75% to 1% per year until the postmenopausal period, when the decline is 2% to 3% per year.2,23,24 However, for men, the decline in bone mass begins at age 50 to 55 with a steady decline of about 1% per year.2,4
Hormonal, genetic, nutritional, and mechanical factors contribute to the age-related decline in bone mass along with immobilization, physical inactivity, and weightlessness.23'24 For example, a 39% calcaneus bone mineral loss was shown in three healthy young men following 36 weeks of immobilization.23 Further evidence that decreased mechanical force on the bone results in loss of bone density has been shown via studies of weightlessness in space. Despite sufficient calcium intake, the bone will lose density unless weightbearing activity is performed.24
Active women have been shown to have significantly higher bone mineral content than inactive women.24,25 Older women (50 to 73 years old) who exercised for 1 hour twice weekly for 8 months increased their bone mineral content 3.5%, while sedentary controls of similar age lost 2.7% during the same period.25 Smith et al showed similar results when older women exercised three times per week.24
Body composition involves analysis of body fat as well as lean body mass (muscle and boneX both of which are affected by aging and exercise. In healthy youth, the body is composed of approximately 10% bone, 30% muscle, and 20% adipose tissue.26 These ratios change with a decline in lean body mass beginning at 1 8 years for women and 21 years for men.27 By age 75, the typical composition is 8% bone, 15% muscle, and 40% adipose tissue.26 This age-related loss in lean body tissue (mostly muscle) and increase in adipose tissue is well substantiated.3,4,26-27
Because exercise stimulates protein synthesis and prevents protein wasting, exercise preserves lean body mass and decreases fat stores.28 Lean body mass has been shown to be maintained until the age of 65 in middle-aged and older athletes (age 40 to 7O).7 The percent of body fat loss ranges from 1% to 6% depending on the individual's participation in a conditioning program or diet.29 Despite consistent training, older athletes will exhibit higher levels of body fat than young competitive runners, although their body fat is much less than for the general population of the same age.5-7 Therefore, as chronological age increases, a wellbalanced diet combined with an appropriate exercise program can preserve muscle mass and decrease fat stores.
Basal Metabolic Rate
Metabolism is influenced by exercise (exercise increases the basal metabolic rate up to 30 times that of restingX30 body temperature, ingestion of food or fluids, hormonal activity, and aging. After the age of 3 years, there is a progressive decline in basal metabolic rate.4'31 In older people, the decrease in basal metabolic rate is due to a decrease in skeletal muscle mass.32 Therefore, if skeletal muscle mass can be maintained with appropriate exercise, the agerelated decline in basal metabolic rate may become less significant.
The thermorégulation system of the human body is an efficient temperature control mechanism.32 However, exercise, excessive heat, humidity, age, and other factors can have a significant effect on the thermoregulatory mechanism.4,33
Age-related and exercise effects on thermorégulation are inconclusive, but older persons have been reported to have less efficient thermal control systems.3,31'32 Both heat gain and heat loss are not as effective in older persons.32 Heat production is decreased due to a decrease in muscle mass and resulting decrease in basal metabolic rate. When exposed to cold, older people begin to shiver later, thereby delaying heat production.32 Exercise is an intervention that may improve the shiver response.34
Heat-loss changes in the elderly have been reported to be related to the sweat response.32 Irion et al (cited in Eisenman33) found that older men had a significantly lower evaporative heat loss, and older women also had a reduced sweat rate.35 Dehydration can also reduce sweat rate and result in an increased rectal temperature.35 The problem of dehydration may be greater in older persons because there is a 10% to 20% decrease in body water between the ages of 20 and 90 years of age,33 and the older person has a decreased sensitivity for acquiring necessary fluids.32
Highly trained individuals are known to have greater adaptive abilities to thermal loads than untrained individuals.30,34 An enhancement of sweating and an increase in forearm vasodilation are among the adaptive abilities34 that can lead to increased dissipation of heat.32 The thermoregulatory modifications contribute to a relatively lower core temperature during exercise and a decreased demand on the heart and circulatory system.34 Because exercise training can increase heat dissipation, enhance shivering, increase muscle mass, and increase VO2, exercise training may improve the thermoregulatory system of older persons. Therefore, the incidence of hypothermia, heat exhaustion, and heat stroke may be reduced.
The nervous system is one of the chief organs and regulators of the body. As the communication and coordination center of the body, the nervous system is involved in sleep patterns, psychological parameters, and cognitive functioning. Generally, aging has a deleterious effect on nervous system functions. However, regular physical activity reduces the agerelated decline in oxygen consumption; therefore, it has been proposed that fit elderly perform better on tests of psychomotor function and intelligence.4'36,37
Aging affects the brain, spinal cord, and the peripheral nerves. Payton and Poland reported that the brain's weight decreases from 10% to 20% between the ages of 20 and 90.18 This decrease in brain cells is due to cell atrophy and death. With a decreased cerebral blood now, brain functions are also decreased. Brain waves slow in healthy elderly persons and sleeping patterns change.18 Learning ability, intellectual capacity, and memory have age-related declines.3,18 Nerve conduction is reduced about 0.4% per year beginning at age 204,18 which results in a decreased reflex response and sensory acuity and an increase in arousal threshold.
FORMULA FOR COMPUTING THE EXERCISE HEART RATE
There is a paucity of research on the relationship among aging, sleep, emotional stress, and physical activity. When healthy middle-aged persons and healthy elderly persons participated in a 10-week training program, the investigators found that the sleep patterns of the exercise group improved 43.8% and 25.9%, respectively, while the control group improved 18.8%.38,39
Studies examining the effect of exercise training on anxiety and depression have produced inconsistent findings.36,37,39 Blumenthal et al found a nonsignificant decrease in anxiety scores after exercise training,39 whereas Dishman found a decrease in state anxiety scores.36 Other studies reviewed by Hughes failed to show sufficient evidence that exercise relieves anxiety.37 Some studies have shown trends toward a decrease in depression when persons participate in conditioning programs,37,39 whereas other studies have shown little evidence that exercise decreases depression.36-37
The age-related decline in cognitive functioning appears to be modified with physical activity.4'36 Older persons who participate in an exercise program have been found to score higher on cognitive and memory tests.37
The need for exercise does not change as a person grows older. Numerous studies have demonstrated that exercise has many benefits for the aging body. Exercise reduces the agerelated decline in VO2 max, reduces mean blood pressure and systemic vascular resistance, preserves lean body mass and decreases fat deposits, increases HDL and decreases triglycérides, increases bone mineral content, improves basal metabolic rate, increases muscle strength, and increases cognitive functioning (Figure 1).
With the many benefits of exercise, it is essential for nurses to include physical activity as an important intervention in plans of care to increase the functional capacity of their adult clients. The exercise prescription (Figure 2) needs to include aerobic exercise at 60% of maximal heart rate (Figure 3)40 at a frequency of at least every 42 hours. If clients already have an exercise program, nurses need to encourage them to maintain their program so the benefits can be realized.
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EFFECTS OF EXERCISE AND AGING ON SELECT BODY SYSTEMS