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Geriatric Fitness: Effects of Aging and Recommendations for Exercise in Older Adults

Posted on: Friday, 25 March 2005, 03:00 CST

ABSTRACT

The process of aging is associated with numerous changes in all bodily systems that ultimately manifest in a decline in peak physiologic function. Preservation of functional ability in advanced age is predicated on maintenance of the 4 components of fitness- cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition-each of which show changes with aging that adversely impact functional ability. A requisite awareness and understanding of the effects of aging on the components of fitness and understanding of the role of exercise as intervention is of paramount importance. This review presents underlying changes and adaptations within each component of fitness and the effects on overall physiologic capacity from the more overt changes underlying declining aerobic capacity, pulmonary function, and flexibility, to the more latent changes such as demineralization of bone leading to changes in body composition and the contraction- specific decline in the force generating capacity of skeletal muscle. Because exercise and physical activity have been shown to attenuate or delay many of the agerelated changes in the components of fitness, recommendations and guidelines for exercise prescription are offered in the context of the these changes.

INTRODUCTION

In the 30-year period from 1965-1995, the United States has witnessed an evolution in the structure of the age classes evidenced by an 82% increase in those over the age of 65 years. Representing 13% of the population in 1995, current estimates are that by the year 2005, those over the age of 65 will account for 20% of the population in the United States. Additional evidence of the increased population of older adults is noted in those over the age of 85 years, considered the 'old old,' which is the fastest growing segment of the population.1

The process of aging in humans is characterized by a multitude of changes in all bodily systems that ultimately result in a decreased capacity to function.2 Although the incidence of pathology and co- morbidity is greater in older populations than in younger, the process of aging itself is nonpathological and presents in a variety of changes manifesting in reduced functional capacity.3 While variability exists in defining an older population, many of the physiologic changes due to aging are observable by the middle of the sixth decade.

While greater variability exists in the general health status of older adults than in younger, one principle remains constant- functional ability at any age is predicated on maintenance of fitness. Fitness, a familiar but often enigmatic term, encompasses 4 distinct health-related components: (1) cardiorespiratory endurance, (2) muscular strength and endurance, (3) flexibility, and (4) body composition. Nonpathological, yet adverse, age-related declines in the 4 components of fitness are considered pre-disposing factors to the declining functional status of the older population. While it is difficult to differentiate what changes in functional ability are due to aging itself and which are secondary to disuse atrophy and diminished activity, lack of activity is, to a greater degree, responsible for the decline in functional ability observed during aging. However, data have shown that many of the adverse age- related changes in the 4 components of fitness can be attenuated or reversed with exercise.4

As the number of older adults in the population steadily increases, the impending need for greater knowledge of the effects of aging on the components of fitness and understanding of the role of exercise as intervention becomes evident. Because evidence continues to show that disease onset, rate of progression, and severity in older adults may be prevented, delayed, or attenuated with physical activity, knowledge and consideration of age-related changes in fitness is necessary to provide efficacious care to the older population.5 Therefore, it is our intent to present a review of age-related changes in fitness and to present current guidelines, recommendations, and special considerations for exercise in older adults.

AGE-RELATED CHANGES IN THE COMPONENTS OF FITNESS

Cardiorespiratory Endurance

The major age-related changes in the 4 principal components of fitness are listed in Table 1. Peak physiological function generally occurs prior to age 30 and thereafter undergoes an age-related decline of 0.75% to 1% per year.6 The cardiorespiratory system, not immune to such changes, shows a significant decline in the capacity for aerobic activity. Maximal oxygen consumption, the primary measure of cardiorespiratory function, decreases 5% to 15% per decade after the age of 25 years.7 The greatest rate of decline appears to occur after age 40 such, that by age 65, there is an approximate 30% decline in maximal oxygen consumption." In absolute terms, maximal oxygen consumption shows an average annual decrement of 0.28 ml.kg^sup -1^.min^sup -1^ to 1.04 ml.kg^sup -1^.min^sup -1^ beginning in the early 20s.9 This decline is largely mediated by age- related decreases in maximal cardiac output, heart rate, and arteriovenous difference.10-13

Table 1. Effect of Aging on Components of Fitness

Maximal cardiac output is reduced 20% to 30% in older adults when compared with younger individuals.4 Three primary factors underlie this reduction: (1) a decline in maximal heart rate of 6 to 10 beats per minute per decade such that the maximal heart rate of a 70-year- old is 25% less than that of a 20-year-old,10,11,13 (2) a decline in stroke volume reflecting decreased left ventricular myocardial contractile performance evidenced by increased end diastolic volumes and reliance on passive properties of cardiac tissue to increase stroke volume (ie, Frank-Starling mechanism),10,12 and (3) a decline in total blood volume, plasma, and red cells.15

A major underlying factor precipitating decline in maximal cardiac output is decreased stroke volume. Decreased stroke volume likely reflects a decline in left ventricular contractility, decreased ventricular compliance during filling, and reduced inotropic responsiveness to sympathetic stimulation (B-adrenergic response).16 Age-related increase in end-systolic volumes during maximal exercise is evidence of the decline in pump mechanics and consequently results in decreased ejection fraction.10,13 Additional evidence of declining myocardial mass, declining Ca^sup 2+^-myosin ATPase activity and, in many cases, cardiac ischemia reflect the underlying mechanisms explaining the gradual loss of contractile strength in the myocardium and resultant decline in stroke volume.10,13

Another principle determinant of aerobic capacity, arteriovenous difference, decreases as a function of aging resulting in decreased maximal oxygen consumption. From age 20 to age 65, arteriovenous difference declines from approximately 16 volumes percent to 12 to 13 volumes percent. Systemic factors underlying this decrease include reductions in fiber-to-capillary ratio, total hemoglobin, and respiratory capacity of skeletal muscle.6 The ability to regulate circulation also appears to change with aging. Autonomie control of blood flow changes with aging such that during physical activity, a disproportionate amount of blood is directed away from working muscle toward the skin and viscera-areas with limited ability to extract oxygen.

Additional factors leading to decreased cardiorespiratory capacity with aging include a decline in amount of mitochondrial mass and oxidative enzymes of skeletal muscle, an increase in blood pressure and systemic vascular resistance, reduced dilatory capacity of vessels, reduced baroceptor sensitivity, and reduced orthostatic tolerance.10,14,17 Cellular changes within the cardiorespiratory system impairing oxygen transport and uptake include increased presence of amyloid-, basophilic-, lipid-, and collagen-type substances in the myocardium and major blood vessels decreasing the vessel compliance. Collectively, these adverse changes result in decreased responsiveness to changes in pressure and volume within the heart and vessels and reduce the capacity for cardiac function.18

With changes similar in magnitude to those seen in the cardiovascular system, the pulmonary system likewise demonstrates age-related decreases in functional capacity affecting aerobic performance. While a younger pulmonary system is characterized by a significant reserve capacity capable of adapting to ventilatory demands, a progressive reduction in this capacity for adaptation occurs between the ages of 30 and 60 years, worsening in later years.6 As a function of aging, the pulmonary system demonstrates 3 major signs of advancing age. The first, a gradual increase in the size of the alveoli, is accompanied by a decline in alveolar vascularity leading to a decrease in viable surface area for diffusion. This results in reduced rate and quantity of gas exchange. The second, loss of elastic support structure in the lungs, leads to loss of elastic recoil and premature closure of airways impairing ventilation. The result is an increase in physiologic dead space and reduced volume for gas exchange. As a consequence, ventilation rate increases while tidal volume decreases- a common finding in older adults.6 Third, a weakening of respiratory muscle, along with lossof elasticity, makes expiration more difficult and increases work of breathing.

The magnitude of change seen in the pulmonary system with aging is similar to that in the cardiovascular system. Despite these changes and excluding pathology, pulmonary function remains adequate during exercise conditions in older adults.6 Thus in older adults, as in younger adults, the limiting factor with aerobic capacity does not appear to be pulmonary function, but rather cardiac output.

Muscular Strength and Endurance

The ability to function within one's environment and maintain a high quality of life is of paramount importance to an individual as he or she progresses into the later years of life. A major concern facing older adults and researchers studying aging is the loss of skeletal muscle mass, known as sarcopenia,19 and the associated loss of voluntary strength. However, the detrimental effects of skeletal muscle loss extend beyond the decreased ability to generate force. Resting metabolic rate, regulation of blood glucose, maintenance of core temperature, and the protection of internal structures (bones, organs, nerves, and blood vessels) are all dependent on skeletal muscle tissue and are consequentially affected by loss of muscle tissue.20

Sarcopenia, a process of normal aging, is not likely to be explained by a single cause, but rather by a number of contributors, each adding in varying degrees to the age-related loss of skeletal muscle mass. Possible contributors include endocrine changes, altered cytokine activity, altered protein synthesis and proteolysis, physical inactivity, nutritional factor, and changes in neurological factors.21 The effects of these contributing factors on skeletal muscle mass have 3 consequences: (1) the loss of motor neurons from motor unit remodeling resulting in loss of muscle fibers, especially type II muscle fibers;22,23 (2) the reduction in muscle fiber size affecting type II muscle fibers selectively,24 while type I muscle fibers appear spared the effects of aging; and (3) an increase in the amount of noncontractile tissue, fat, and connective tissue within the muscle belly is substantially increased in older adults.25-27

It is logical that the marked reduction in muscle mass observed with aging would have an adverse effect on voluntary muscle strength and the ability to generate force. Observations from longitudinal study of changes in muscle strength suggest that the quantitative loss of muscle cross sectional area with progressing age is a major contributor to the reduction in voluntary muscle strength.28 While the onset of strength decline is variable, it is generally observed that muscle strength is fairly well maintained through the forties and fifties.29,30 However, once beyond the sixth decade, muscle strength steadily declines with the total decrement in voluntary muscle strength ranging from 30% to 45%.31

Generalized loss of strength with aging, while easily observed, differs in magnitude depending on the specific muscle contraction type examined (Figure 1). Isometric (ISO) muscle strength, measured when there is no change in the muscle length under load, appears to be lost at approximately 1% to 1.5% per annum after the sixth decade.32 It is not uncommon for healthy older adults in their 60s and 70s to exhibit 20% to 40% less voluntary ISO strength than their younger counterparts, while the very old (80 years or more) can demonstrate reductions in voluntary ISO strength of 50% or more.31

Figure 1. The curvilinear relationship between age and maximum voluntary strength in the human life span. Reprinted with permission from Muscle & Nerve.31 Copyright 2002, John Wiley & Sons, Inc.

The age-related loss of voluntary concentric (CON) strength, measured as the muscle is allowed to shorten under load, demonstrates reductions similar to ISO strength. Concentric strength can decline as much as 56% by the ninth decade.33 Akima et al34 confirmed that CON strength of the knee extensors at various angular velocities was significantly decreased in men in their 40s, 50s, 60s, and 70s when compared to men in their 20s. Further evidence of the substantial reduction in CON strength was offered when Frontera et al28 concluded that loss of CON knee extensor and flexor strength of older adults ranged from 23.7% to 29.8% at angular velocities of 60 and 240/s. The average rate of decline for CON strength of the knee extensors and flexors is reported to be 14% and 16% per decade, respectively, for both men and women.35 Concentric strength loss is not only limited to the quadriceps and hamstring muscles. Several studies have found CON strength deficits with aging in various other muscles, eg, Poulin et al36 (elbow extensors), Porter et al37 (dorsiflexors), and Hughes et al35 (elbow flexors & extensors). The loss of CON strength with aging may be so severe that the very old often fall below the minimum level required to perform activities of daily living (Figure 1).33

The third and least studied measure of muscle strength is eccentric (ECC) force, measured as the muscle lengthens under load. The lack of information regarding ECC strength in older adults is extremely surprising since ECC contractions are an integral part of many activities that often cause older adults difficulties (eg, deceleration of the body during walking & descending stairs) and because ECC strength can be measured reliably using isokinetic dynamometers.38 It was not until the last several years that ECC muscle strength has been examined in older adults and ample evidence has shown that ECC muscle strength is less affected by the aging process than ISO and CON strength.36,39-41 Preservation of ECC muscle strength is supported by the work of Porter et al,39 Hortobagyi et al,42 and Bellew and Yates.41 Both Porter et al39 and Bellew and Yates41 concluded that peak torque in older men and women, when expressed as a percentage of young, was greater for ECC contractions than concentric or isometric. Similarly, Hortobagyi et al42 reported that younger subjects showed significantly greater CON strength when compared to older adults; however, there was no difference between younger and older ECC muscle strength. Furthermore, regression analysis revealed that ISO and CON strength declined 32N (7.21b) and 31 N (6.91b) per decade, respectively, while ECC muscle strength declined only 9N (2.01b) per decade.42 In general however, it appears that the normal aging process that severely diminishes ISO and CON muscle strength in later life does not affect ECC muscle strength to the same degree (Figure 1).

The mechanisms underlying the preservation of ECC strength in older adults are not fully understood but may stem from the age- related structural and functional changes within the muscle. Hortobagyi et al42 proposed the following potential mechanisms for the preservation of ECC strength with aging: (1) increased contribution of passive elements (ie, connective tissue), (2) decreased sarcomere instability with aging, and (3) modification to the detachment and reattachment sequence of actin-myosin cross- bridges.

Flexibility

Flexibility is generally considered the ability to move one or more joints through a complete range of motion. The American College of Sports Medicine (ACSM) expands this definition to encompass the functional use of available range of motion thus, flexibility is considered the range of motion of a single or multiple joints and the ability to perform specific tasks.41 Regardless of the presence or lack of pathology in old age, declining range of motion is pervasive in older adults and data show that loss of flexibility and joint range of motion result in a decline in function.44-46

Evidence for declining joint range of motion in older adults is plentiful.47-50 Investigators examining loss of flexibility in cross- sectional designs consistently report a progressive decline in mobility of spinal and peripheral joints with aging.47,50 Previous data have shown that, as a function of aging, flexibility generally decreases 20% to 30% from age 30 to 70.51,52 However, a significant decline in spinal mobility of up to 50% has been reported in older adults into their late 70s.51,52 The rate at which joint flexibility declines also appears to differ between upper and lower extremity joints. Data from subjects 18 to 88 years of age have shown a less precipitous rate of decline in joints of the upper extremity than in lower extremity joints.46 Lung et al45 have suggested that this observation is due to the continued use of the upper extremities throughout life when age-related decline in mobility and activity may diminish use of the lower extremities.

Much of the loss in flexibility or joint range of motion is a manifestation of age-related changes in the musculotendinous unit and biochemical, or viscoelastic, properties at the tissue level, particularly in the primary supportive protein of connective tissue, collagen.41 In younger years, collagen fibers show a more uniform, parallel formation-a formation that is conducive to stretching and lengthening. With aging, collagen fibers begin to lose their parallel orientation, likely due to declining solubility and increased crosslinking of tropocollagen, the fundamental unit of collagen fibrils.53 These structural changes in the soft tissue matrix lead to a decrease in the linear pull relationship in the collagen tissue ultimately resulting in decreased extensibility of the connective tissue. Such changes in the mechanical properties of soft tissue are readily noted in the length-tension relationship with a greater rate of increase in tension per unit change in length of older muscle versus younger muscle.54

The decline in flexibility of the muscle complex is reportedly due to an increase in the stiffness or rigidity of the noncontractile structures with age, which include skin, connective tissue, joint capsule, extracellular fluid, cartilage, ligamen\ts, tendons, and blood vessels.54 When considering the relative contribution to joint stiffness of nonmuscle versus muscle tissues, the significance of the loss of pliability in the nonmuscular tissue becomes apparent. The degree to which specific soft tissues contribute resistance to joint range of motion has been quantified.51 In order of magnitude, the joint capsule accounts for 47% of the total resistance to joint movement, muscle and fascia 41%, ligaments and tendons 10%, and skin 10%.51 From these data, the nonmuscular tissue, the tissue that shows significant change with age, accounts for the majority of the resistance to passive joint motion.

Further evidence of age-related increase in intramuscular connective tissue appears to be related to the predominant skeletal muscle fiber type present. The magnitude of collagen deposition and crosslinking appears to be dependent on whether the muscle is primarily comprised of slow-twitch or fast-twitch skeletal muscle fibers.55 Tissue analyses of predominantly slow-twitch muscles (ie, soleus) and fast-twitch muscles (ie, extensor digitorum longus) have shown more extensive presence of age-related collagen crosslinking in muscles that are predominantly fasttwitch muscles. With aging, an increase in the presence of collagen crosslinking in both the contractile and noncontractile tissues necessarily results in a decreased ability to lengthen the muscle-tendon unit.56 As a result, the ability to move the joint decreases and flexibility is diminished.

Evidence of age-related changes in the ligamentous tissue also reflects loss of flexibility. By middle age, both ligament and ligament insertional bone begin to show evidence of weakening.57 Decreases in the viscosity of ligaments in combination with increased collagen crosslinking leads to less compliance and greater loss of joint range of motion over time.58 Additional age-related changes within the joint such as formation of osteophytes and the onset of degenerative joint disease are also likely causes of the decrease in joint range of motion with aging.1

Body Composition

Body composition is most simply defined as the relative proportion of fat and fat-free tissues within the body.59 Because obesity and excessive fat content are associated with increased risk for a variety of chronic diseases, such as coronary artery disease, hypertension, hyperlipidemia, and certain cancers, assessment of body composition provides a method of establishing optimal weight and fat content for health and physical performance.59 However, whereas body composition analysis is most commonly used for establishing guidelines in younger adults prior to the onset of disease and in athletes to optimize performance by monitoring changes in lean versus fat components, use of body composition analysis for these same purposes in older adults is much less common. This is likely due to the fact that many of these disease processes may already be present in the older population or use for optimization of sport performance does not necessitate such methods.

Analysis of body composition in its most fundamental form divides bodily mass into fat mass and lean mass. Separation of bodily tissues into these 2 distinctions is referred to as the 2- compartment model of body composition. The lean body mass is fat- free weight and includes the skeleton, total body water content, muscle, connective tissue, organ tissue, mineral content, blood vessels, and teeth. Fat mass is composed of essential and nonessential fat stores. Essential fat is generally considered the lipids that are part of the tissues and organs such as the brain, nerves, heart, lungs, liver, and mammary glands whereas nonessential fat is found in the adipose tissue.

Because many of the specific tissues in the fat and lean compartments are affected by the processes of aging, their relative contribution to the overall body composition changes. The most overt age-related change in body composition initially observed is an increase in gross body weight secondary to accumulation of fat tissue. Beginning in the mid-20s, body weight steadily increases and continues until the mid-50s, and then begins a slow decline thereafter.6 This gain in body weight is primarily due to an increased deposition of adipose tissue-the nonessential fat. From the late teens to approximately age 60, percent body fat in males increases from an average of 15% to 28%. Similarly, women over the same time period show an increase in percent body fat rising from an average of 25% to 39% by age 60.6

While the amount of fat increases as a function of aging, the distribution of bodily fat also changes. Whereas in younger years a greater proportion of the adipose tissue is stored subcutaneously, with aging, a greater proportion of the fat is located internally, or viscerally. Because of this, body composition assessment using skinfold techniques must be certain to use equations specific to older adults lest erroneous interpretations be made.

A primary mediating factor underlying the increase in bodily fat is an age-related decline in metabolic rate. From approximately age 20 years to 65 years, metabolic rate decreases about 10% with an additional 10% decline noted thereafter.6 This decline in metabolic rate is the result of numerous factors including declining participation in physical activity, cardiovascular limitations, and changing endocrine function. But perhaps no one factor has a more significant impact on metabolic rate than does age-related loss of skeletal muscle-sarcopenia. Loss of viable, metabolically active muscle tissue not only has a direct effect on total body composition by decreasing the fat-free, or lean, portion of total body mass, but also an indirect effect by decreasing metabolic rate and reducing caloric expenditure.

Because the bony skeleton contributes a significant portion to the overall fat-free mass, age-related loss of bone and mineral content adversely affects body composition. Bone mass generally peaks in the mid-to-late 20s and is thereafter followed by a near linear decline.60,61 Age-related loss of bone occurs in both men and women affecting women twice as often as men. The general rate of bone loss is less precipitous in men than women, estimated at 0.3% per year for men. Initially, the rate of loss in women is similar but quickly escalates to 2% to 3% on an annual basis from the perimenopausal period until 5 to 8 years following menopause.60 By age 90, data suggest that women will lose nearly 50% of the maximal bone mass in the axial skeleton and approximately 30% in the appendicular skeleton.60-62

CURRENT GUIDELINES AND RECOMMENDATIONS FOR FITNESS IN OLDER ADULTS

Commensurate with their increase in the general population, the presence of older adults in clinical environments has risen. Greater demand, therefore, is placed on clinicians to understand the aging process and the differences in physiologic capacity in older versus younger adults. When considering exercise for older adults, certain fundamental principles must be acknowledged: (1) aging does not occur uniformly across the population therefore, chronological age does not necessarily reflect physiological age; (2) knowledge of the normal effects of aging on variables measured during exercise is critical; (3) differentiation of changes in fitness due to age- related decline, deconditioning, and pathology is difficult; (4) while aging itself is imminent, its rate may be amenable to exercise; (5) the existence of an active or latent disease process is more likely in older adults than younger; (6) older persons are more likely than younger persons to be taking medications which may dampen or exaggerate the normal physiologic responses to exercise or alter the capacity to perform exercise; and (7) exercise training does not prevent the process of aging, but it does increase functional ability.63,64

The most common chronic diseases present in older adults are coronary artery disease, arthritis, hypertension, diabetes mellitus, and obesity.17 Used as intervention, exercise is known to attenuate or reverse many of the manifestations of these disease processes. Despite convincing evidence of the benefits of exercise in advanced age, the US Department of Health and Human Services' report on physical activity and health reported that less than 25% of older adults engage in physical activity on a regular basis at a level appropriate to improve physical capacity.65 Perhaps contributing to this sedentary pattern is the observation that today's older population was raised at a time prior to the widespread recognition of the benefits of exercise and during a time when exercise in the later stages of life was not common and was, in many cases, discouraged as too stressful, injurious, or inappropriate for older adults. Only in the last few decades has exercise, including aerobic exercise and resistance training, become a recommended part of a healthy lifestyle for older adults. The acceptance of exercise in old age is evidenced by the American College of Sports Medicine's 1998 issuance of its Position Stand on Exercise and Physical Activity for Older Adults which included exercise recommendations and guidelines for older adults, including the frail and very old.1

The American College of Sports Medicine (ACSM) is recognized as a leading authority for recommendations and guidelines for exercise prescription and testing for special populations including older adults. Its guidelines are widely accepted and used in laboratory and clinical settings. The ACSM guidelines for risk stratification prior to exercise participation specify that persons categorized as low- to moderate-risk may participate in exercise at an intensity of 40% to 60% V0^sub 2max^ without an exercise test.63 However, older adults necessitate special consideration. According to ACSM guidelines, men greater than 45 years of age and women greater than 55 are,by age alone, determined to be at moderate risk, and high risk with one or more signs or symptoms suggestive of cardiovascular or pulmonary disease (Table 2). It is recommended that individuals at moderate risk have a current medical examination (within 1 year) for vigorous exercise and a physician present for maximal exercise testing, but for those at moderate risk, ACSM guidelines do not specify the need for these with moderate exercise or submaximal testing. Those at high risk are recommended to have a current medical examination and presence of a physician during submaximal and maximal exercise testing.59 Use of a screening questionnaire such as the Physical Activity Readiness Questionnaire (PAR-Q) can help to identify those with preexisting conditions in these individuals prior to exercise testing or beginning an exercise program.

More recently, ACSM guidelines for exercise have followed the 'FITT' principle-where 'F' represents frequency of exercise in days per week; 'I' represents intensity as percent of maximal capacity; 'T' represents time, or duration, of exercise; and 'T' represents type, or mode, of exercise.63 A tabular summary of the ACSM's exercise prescription recommendations for cardiovascular, muscular, and flexibility components of fitness is presented in Table 3.59 In keeping with the FITT principle, ACSM recommendations for the cardiovascular, muscular, and flexibility components of fitness are discussed.

Cardiorespiratory Endurance

According to the FITT principle, older adults should engage in cardiovascular exercise a minimum of 3, but preferably all, days of the week at an intensity range of 40% to 85% heart rate reserve (HRR) or maximal oxygen uptake reserve (VO^sub 2^R) (Table 2). If exercising at the higher end of the range, exercise should be performed 3 days per week, alternating days of vigorous cardiovascular exercise with days of low intensity or no cardiovascular exercise. Intensity of exercise must be considered in the context of the overall health status of the individual. An initial conservative approach is advocated. Initiation with low intensity exercise should minimize the onset of musculoskeletal complications while increasing compliance. Intensity guidelines established for aerobic exercise in younger adults generally can be applied to older adults.63 As such, an exercise intensity between 55% to 65% and 90% of maximum heart rate (HR^sub max^), or between 40% and 50% and 85% of VO^sub 2^R or HRR is recommended.

Because deconditioned or persons of lower fitness levels may demonstrate improvements in cardiorespiratory function at intensities less than 50% HRR or 55 to 64% HR^sub max^, the broad range of exercise intensity is intentional. For those at greater levels of fitness, the higher end of the intensity range may be required to demonstrate further adaptation or to maintain current fitness. The ACSM's Guidelines for Exercise Testing and Prescription states that these ranges have been used for nearly 30 years to increase favorably maximal aerobic capacity in primary and secondary prevention programs.63

Table 2. Signs and Symptoms of Cardiovascular and Pulmonary Disease. Reprinted with permission from Lippincott Williams & Wilkins. ACSM's Health-Related Physical Fitness Assessment Manual. Dwyer GB, Davis SE, eds. Philadelphia, Pa: 2005:44. Copyright 2005, Lippincott, Williams, & Wilkins.

Table 3. Exercise Recommendations Using ACSM's 'FITT' Principle. Reprinted with permission from ACSM's Guidelines for Exercise Testing and Prescription. 6th ed.63 Copyright 2000, Lippincott Williams & Wilkins.

Some differences do exist however, when applying these guidelines to older adults. One such difference is the recommended use of a measured peak heart rate versus an age-predicted maximal heart rate. This is predicated on the variability in peak heart rate in persons over 65 years of age. Secondly, controversy exists over the use of a percentage of heart rate reserve or use of a percentage of maximal heart rate when prescribing exercise for older adults.66 More recent ACSM guidelines recommend use of heart rate reserve whereas other experimental data suggest using heart rate expressed as a percentage of maximum. Kohrt et al66 assert, that in healthy older women 60 to 72 years, prescribing exercise intensity as a percentage of heart rate reserve is not recommended because it is not equivalent to percent VO^sub 2max^ and use of heart rate reserve necessarily results in exercise being performed at a higher than expected percentage of maximal aerobic power as based on ACSM guidelines for exercise prescription. Therefore, when prescribing exercise in older adults, Kohrt et al66 advocate use of heart rate expressed as a percentage of maximal heart rate versus percentage of heart rate reserve.

Because maximal aerobic capacity is lower in older adults, at any absolute submaximal work rate an elderly individual is closer to anaerobic threshold compared with someone who is younger.67,68 For example, if a 20-year-old subject with a VO^sub 2max^ of 60 ml.kg^sup -1^.min^sup -1^ and a 60-year-old subject with a VO^sub 2max^ of 40 ml.kg^sup -1^.min^sup -1^ each exercise at the same absolute work rate of 20 ml.kg^sup -1^.min^sup -1^, the younger subject is exercising at a relative work rate of 33% while the older subject is at 50%, thus closer to the anaerobic threshold. However, evidence shows that when exercising at the same relative intensity (ie, same percentage of VO^sub 2max^ or percent heart rate max), older adults perceive the exercise to be easier than do younger adults.66 This results in a similar relative, but lower absolute work load for the older adult. Using the same example subjects and a relative work rate of 50% VO^sub 2max^, the younger subject works at 30 ml.kg^sup -1^.min^sup -1^ whereas the older subject works at 20 ml.kg^sup -1^.min^sup -1^, thus a lower absolute work rate. It is possible that the difference in perceived exertion is related to a reduction in lactate production secondary to a lower absolute work rate.66 The lower absolute work rate would likely show less recruitment of type II skeletal muscle fibers and thus a dampened lactate response.66

Recommendations for time, or duration, of cardiovascular exercise vary based on the health status of the individual. However, 30 minutes of continuous or cumulative aerobic exercise is recommended. The ACSM guidelines suggest that for those who cannot sustain 30 minutes of continuous aerobic exercise, use of shorter bouts of 10- minute periods throughout the day is acceptable. Of course, those with greater initial fitness are advised to engage in continuous exercise for 20 to 60 minutes. With regards to exercise progression and the FITT parameters of intensity and time, the ACSM recommends that older adults initially increase exercise time (duration) rather than intensity.

The type, or mode, of activity one uses for cardiovascular exercise should be individualized as well. Because overt or latent arthrogenous pathology such as osteoarthritis is more common in older adults, exercise mode should be one that does not present excessive skeletal stress. To increase compliance, the activity should be accessible and of minimal cost, thus walking is highly recommended for cardiovascular exercise. With groups of individuals for whom weight-bearing exercise such as walking is not feasible, aquatic and stationary cycle activities are suitable alternative modes of cardiovascular exercise.

Muscular Strength and Endurance

Only in the last few decades has resistance training become a widely accepted form of exercise for older adults. Studies have demonstrated that the aged human is able to respond to resistance training as well as and, in many cases, demonstrate superior relative increases and functional gains than younger populations,69 even in adults into their tenth decade of life.70 The appealing nature of resistance training in combating sarcopenia is its ability to yield increases in muscle mass (hypertrophy) and maximal strength. Furthermore, resistance training has been shown to increase the fiber area of type I and both type IIa and IIb muscle fibers, and increase the total cross-sectional area (CSA) of the leg extensor muscles in healthy older women.71 Additional reported benefits of resistance training in older adults include increased power, increased reaction time, improved control of balance, increased endurance, improvements in body composition secondary to loss of fat mass and addition of lean mass, and an increase in general physical ability.29,71 However, current guidelines for exercise in older adults recommend that resistance training be used as a supplement to cardiorespiratory exercise rather than the sole means of exercise.63

As with the application of cardiorespiratory exercise, a resistance training program must be tailored to the individual needs and abilities of the person and, since the health status of older adults is so variable, great variation exists when designing resistance training programs for older adults. What remains principle to all resistance training programs is the idea that progressive overload is necessary for adaptation. That is, progressive placement of greater than normal demands on the musculature is necessary to stimulate the positive adaptations resulting from such loading.72

In keeping with the FITT principle, resistance training should be performed 2 to 3 days per week with at least 48 hours between sessions. Study of the optimal number of training sessions per week was performed by Taaffe et al73 who examined the effects of 1, 2, or 3 training sessions per week on neuromuscular performance in older adults 65 to 75 years of age. Once or twice weekly training sessions produced similar increases in muscle strength when compared to 3 times per week. Based on the available data, novice and previously untrained older adults should begin with 1 to 2 se\ssions per week, increasing to 3 when they have shown a positive response to the resistance training and demonstrated proper lifting technique.

A single set of 10 to 15 repetitions at a self-perceived exertion of 9 to 11 on the Borg scale (very light to light) for inexperienced persons, and 12 to 13 (somewhat hard) for experienced persons is the recommended intensity.63 It is recommended that when selecting resistance training exercises for a participant one should start with 8 to 10 exercises with one exercise per major muscle group.74 Major muscle groups include quadriceps, hamstrings, pectorals, latissimus dorsi, biceps, and triceps. Similar to recommendations for cardiorespiratory exercise, as strength increases, the overload principle is maintained by first increasing the number of repetitions, then by gradually increasing the resistance. Using the single set of 10 to 15 repetitions guidelines, progressive overload is elicited by increasing the resistance only when an individual can perform 15 or more repetitions at the present load, not before.

The time, or duration, parameter of resistance training is a product of the total volume of the training session. Volume is the total amount of weight lifted in a session and is a product of the number of repetitions, number of sets, and load of each repetition.72 For example, high loads cannot be lifted for many repetitions whereas lower loads can, thus requiring more time (duration). A duration of 20 to 30 minutes is attained if adhering to the FITT principle for resistance training. However, the literature has often demonstrated that older and even frail older adults are capable of benefiting from greater volumes performing 2 to 3 sets,75-78 and often 4 to 5 sets79,80 at high training intensities. In general, 1 to 3 sets is sufficient to bring about the required adaptations to the skeletal muscle system and the number of sets should be determined in accordance with the experience level of the participant, ie, begin performing one set and increase the number of sets with experience.74 Because resistance training can take many forms-free weights, Nautilus, Universal, pulleys, body weight resisted exercise-the type (mode) of resistance exercise is variable.

There are of course special considerations when using resistance training in older adults. If able, resistance training using machine devices is preferred over free weights as machines require less coordination, provide stability for the body, permit use of low initial loads, allow smaller increases in load, permit more controlled range of motion and thus, are less likely to result in injury.74 Use of explosive, ballistic exercises is discouraged in favor of slow, controlled motion throughout the available range of motion. Whereas the attempted expiration against a closed glottis (Valsalva maneuver) may improve lifting performance in experienced athletes, older adults should be encouraged to maintain their normal breathing pattern during resistance training, or even exhale during the lifting phase of the movement.81

A final consideration lies in the quantification of strength. The traditional method of quantifying maximal strength in younger populations is to measure the maximal amount of load that can be lifted through a full range of motion in one repetition-a one repetition maximum (1RM).72 Until recently, use of this technique was not advocated in older adults due to the general, yet unsupported, idea that use of such strenuous activities in this population would lead to injury and harm. However, a recent review of this methodology in older adults has shown that, when controlling for pre-existing injury and pathology, injury rates among older adults are no different than in any other age group and that the disinclination toward the use of the 1RM is unfounded.82

Flexibility

A flexibility training program is a planned, deliberate, and regular program of exercises intended to progressively increase the usable range of motion of a joint or set of joints.43 Age-related decline in activity level and disuse result in shortening of soft tissues whereas active movement promoting increased localized circulation promotes increased pliability of soft tissues and increased flexibility.56 Thus, the basis for exercise and physical activity as interventions to age-related loss of flexibility is the empirical observation that range of motion and soft tissue extensibility can be improved with exercise.

Reports on the efficacy of exercise interventions are somewhat variable. Intervention studies have reported significant improvements in flexibility in major joints of the body following participation in various types of exercise programs while others report no association between exercise activity level and flexibility.83-86 More recent studies using resistance training or Tai Chi as exercise have shown improved range of motion in previously inactive older adults.87,88 Despite these findings, evidence-based guidelines for flexibility programs in older adults are limited due to methodological flaws including small sample size, lack of randomization, and poorly defined groups and exercise parameters. As a result, identification of specific parameters for a flexibility protocol is not feasible, thus a clear dose-response relationship does not exist. Perhaps this lack of evidence is the manifestation of the generalized lack of attention given to flexibility exercises in comparison to cardiovascular and muscular strengthening activities. Nevertheless, much of the data that are available suggest that flexibility can be improved and mobility enhanced through participation in exercise-and not specifically flexibility exercises but exercise in general.

Application of the FITT principle to flexibility can be made based on guidelines from the ACSM. Stretching exercises as part of a flexibility program should be performed 2 to 3, or more, days per week. More specifically, these stretching exercises should be incorporated into a more comprehensive exercise program integrating cardiorespiratory and muscular strengthening activities. Each exercise should be performed at an intensity such that the degree of stretch induces a mild discomfort but not pain with the movement being smooth and at a slow to moderate speed, rather than ballistic. Following a brief warm-up, current recommendations are for a 10 to 30 second stretch with at least 4 repetitions per stretch. The duration, or time, of the program should be long enough to sufficiently stretch the major muscle groups.

Flexibility activities are noted in different types, or modes, of popular exercise programs including Tai Chi, calisthenics, yoga, and Pilates. However, it is recognized that other aerobic exercises such as walking, dance, cycling, etc, can increase range of motion. Thus, improvements in joint range of motion may occur through participation in specific stretching exercise programs, or as part of other cardiorespiratory and muscular exercise programs. Nonetheless, current guidelines for fitness in older adults advocates the incorporation of specific stretching exercises in any exercise program for older adults.63,89

CONCLUSION

The process of aging imposes numerous changes in the functional capacity of the human body. Cardiorespiratory endurance, muscular strength and endurance, flexibility, and body composition all show adverse changes as a function of aging. Efficacious delivery of clinical care is predicated on knowledge of the normal physiological changes occurring with aging and the manifestations on functional capacity are requisite when working with older adults. While the degree to which a lifestyle void of physical activity contributes to age-related decreases in fitness remains unclear, 4 conclusions may be drawn from the available body of scientific knowledge: (1) exercise as an intervention is useful for maintaining and optimizing the components of fitness in older adults; (2) musculoskeletal function is improved with a balanced program of cardiorespiratory, resistance training, and flexibility activities; (3) older adults who have remained physically active do not undergo a decline in fitness to the same extent as those who have been inactive; and (4) despite aging, older adults can experience adaptation to exercise in a manner similar to that of younger adults.90

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James W. Bellew, PT, EdD;1 T. Brock Symons, PhD;2 Anthony A. Vandervoort, PhD3

1 Associate Professor of Physical Therapy and Director of Research, Osteoporosis Center at the Louisiana State University Health Sciences Center, Shreveport, LA

2 Post-Doctoral Fellow in the Division of Rehabilitation Sciences, School of Allied Health Sciences, The University of Texas Medical Branch, Galveston, TX

3 Professor, Schools of Physical Therapy and Kinesiology, Faculty of Health Sciences, University of Western Ontario, London, Canada

Address correspondence to: Jim Bellew, PT, EdD, 1501 Kings Hwy, Rm 310 SAHP, Shreveport, LA 71130, Ph: 318-675-6821, Fax: 318-675- 4208 (jbelle@lsuhsc.edu).

Copyright Cardiopulmonary Physical Therapy Journal Mar 2005

Source: Cardiopulmonary Physical Therapy Journal

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