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Strategies for Aging Well

Geithner, Christina A PhD1; McKenney, Diane R BS2

Strength and Conditioning Journal: October 2010 - Volume 32 - Issue 5 - p 36-52
doi: 10.1519/SSC.0b013e3181d9a66c
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AGE-RELATED CHANGES IN STRUCTURE AND FUNCTION ARE A RESULT OF THE SINGULAR AND INTERACTIVE EFFECTS OF GENETIC AND ENVIRONMENTAL FACTORS AS WELL AS NORMAL TIME EFFECTS, DISUSE OR PHYSICAL INACTIVITY, AND DISEASE. ONE OF THE MOST EFFECTIVE STRATEGIES FOR AGING WELL, EXTENDING LIFE EXPECTANCY AND QUALITY OF LIFE, IS TO ADOPT AND MAINTAIN A REGULAR EXERCISE PROGRAM THAT INCLUDES AEROBIC EXERCISE, RESISTANCE TRAINING WITH POWER TRAINING INCORPORATED, FLEXIBILITY EXERCISES, AND BALANCE TRAINING. THIS ARTICLE DISCUSSES AGING DEMOGRAPHICS, DEFINITIONS AND THEORIES, AND RECENT RESEARCH RELATED TO EXERCISE NEEDED TO MAINTAIN OR IMPROVE MUSCULAR FITNESS, FUNCTION, AND QUALITY OF LIFE WITH AGING.

1Department of Human Physiology, Gonzaga University, Spokane, Washington; and 2Department of Physical Therapy, Eastern Washington University, Spokane, Washington

Christina A. Geithner

is a professor in the Department of Human Physiology at Gonzaga University in Spokane, Washington.

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Figure

Diane R. McKenney

is a doctoral student in the Physical Therapy Program at Eastern Washington University in Spokane, Washington.

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INTRODUCTION

Aging demographics indicate a rapid “graying” of the population, with aging “baby boomers” beginning to reach the age of 65 in 2011 accelerating this growth in the United States. The number of individuals older than 65 years in the United States was approximately 37 million in 2006 (25) and just more than 40 million in 2010 (1). The number of individuals of 65 years and older is expected to nearly double by 2030 and will represent approximately 20% of the U.S. population (1,25). The projection for 2050 is more than 88 million of adults of 65+ years, representing 20% of the population (all ages) (1) Life expectancies have increased, but the quantity of added years is not always accompanied by quality of life (25).

Multiple chronic conditions are associated with older age. These negatively impact quality of life through their contribution to functional declines and the inability to remain independent and living in the community. The most prevalent age-related chronic conditions are hypertension, arthritis, heart disease, any cancer, diabetes, asthma, and stroke (14,25). Many chronic conditions can be prevented or ameliorated with behavioral interventions. It is estimated that 35% of premature deaths (not to mention the disabilities associated with chronic conditions) could be averted through not smoking, eating a healthy diet, and exercising regularly (14).

Functional health, the ability to perform both basic and more advanced activities of daily living (ADLs), declines with aging. These changes are because of inactivity-associated deficits in strength, power, endurance, and flexibility. Physical or cognitive function in later years may also be diminished as a result of illness, chronic disease, or injury. In 2005, 42% of people aged 65 years and older reported a functional limitation, and a greater percentage of older women reported functional limitations than men (25). Indicators used to monitor functioning includes limitations in ADLs, such as bathing, eating, using the toilet, and walking across the room; instrumental activities of daily living (IADLs), which include activities such as shopping, housework, and meal preparation; and measures of physical, cognitive, and social functioning (25). Aspects of physical functioning such as walking, stooping, or reaching are more closely linked to physiological capabilities than are ADLs and IADLs (25). The rate of difficulty in performing physical functions increases progressively after age 65 and more sharply in the 80s (17).

Given the aging of the population, the increasing prevalence of chronic conditions with age, and age-related declines in fitness and function, the exercise professional who is educated about older adults and the issues they are likely to face as they age will be better able to assist this segment of the population in aging well. He or she will be able to help older adults realize fitness gains, particularly in muscular strength, power, and endurance, which have significant implications for physical function and quality of life. The purposes of this article are to provide exercise professionals with information that will help them to effectively work with older adults to reduce age-related declines in fitness and function via appropriate exercise prescription and to give aging readers information to assist them in aging well. Age-related changes in physical structure and function are identified, resistance training is discussed as an antiaging intervention, existing research on resistance training to enhance muscular strength and power as well as physical function is reviewed, and suggestions for exercise prescription for muscular fitness and function are offered.

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AGING AND AGE-RELATED CHANGES

Each of us is aging from the moment we are conceived until the moment we die. The complete process of aging may be said to go from “sperm to worm” (106, p. xx). When we are born into this world, we are dependent on others. As we grow and mature, we increase in size and function and we mature physically. As we age further, we lose functional capacity. Aging is most often defined as this functional decline over time.

Aging categories that have been identified include chronological aging, cosmetic aging, social aging (changes in interactions with others with age), psychological aging (age-related changes in perception and behavior), and economic aging (changes in financial status with age) (20). Aging may result from disuse or reduced physical activity, disease, and age-related causes and their interactions. Functional losses fall into 4 categories: (a) functions totally lost, (b) structural changes, (c) reduced efficiency, and (d) altered control systems or reduced reserve capacity to respond, or changes in homeostatic processes (106).

Two types of aging are commonly identified in the literature: normal or eugeric aging, which refers to the changes in function that are not produced by disease, and pathogeric or pathological aging, which refers to the effects on the aging process resulting from environmental perturbations, genetic mutations, and accidents of nature or the human environment (106).

A third type of aging is optimal aging in which function is preserved at the highest level and quality of life is maintained. Successful aging, as proposed by Rowe and Kahn (90), is the balance of 3 components: absence of disease and disease-related disability, high functional capacity, and active engagement with life. In optimal or successful aging, independence and quality of life (which incorporates physical health, psychological state, level of independence, social relationships, personal beliefs, and relationship to salient features in the environment (115)) are preserved, and healthy life expectancy is extended. A physically active lifestyle is a key contributor to aging successfully or aging well. In fact, physically active older adults are more than twice as likely to be rated as aging successfully, even after controlling for demographic covariates (5).

Inevitable structural and functional changes occur with age in major organ systems (4,106). These are summarized for selected organ systems in Table 1. Some of the changes that have the most deleterious effect on functional performance and quality of life are those that affect the muscular system. Sarcopenia is a Greek term meaning “poverty of flesh” and refers to the loss of muscle mass and strength because of aging, having a muscle mass index (muscle mass in kilograms/height in meters squared) less than 2 standard deviations below the mean for a young age group (61). Approximately 10-25% of adults younger than 70 years and more than 40% of the elderly older than 80 years are sarcopenic (61). Muscle mass is lost at a rate of 1-2% per year after age 50, and strength declines to a greater degree (61). Much of this loss in muscle mass can be attributed to age-related processes; however, reductions in physical activity with age that result in disuse atrophy are also to blame (93). Significant reduction in muscle mass, sarcopenia, results in muscle weakness and functional limitation in the elderly. Sarcopenia is associated with mitochondrial dysfunction and the accumulation of mitochondrial DNA (mtDNA) deletions (105).

Table 1

Table 1

Table 1

Table 1

Age-related loss of muscle fiber number and size alone fail to account for the magnitude of age-related strength loss (7). The strength decline with age occurs about 3 times faster than that in muscle mass (2.6-4.1% per year), suggesting a decline in muscle quality (34,59). From the second to tenth decades of life, there is an average motor unit (MU) loss of 25% and up to a 50% loss in total MU number (7). MUs are remodeled with aging resulting in a decrease in the total number of viable MUs. Age-related neural degeneration preferentially affects type II muscle fibers, and reinnervated by larger MUs, changing them from fast-fatiguable to fast-fatigue-resistant fibers. Remodeling of MUs results in decreased muscle strength or the ability to produce large forces, decreased rate of force development, and reduced control of force output (7). Age-related neural changes that affect muscle function include reduced activation of agonistic muscles and greater coactivation of antagonists (59). Fortunately, we can slow or even reverse some of these aging-related declines with exercise training.

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ANTIAGING INTERVENTIONS

Two interventions known to enhance skeletal muscle function, and thereby protect against age-related muscle loss, are caloric restriction and exercise training, particularly resistance training. Recent research by Hepple et al. (42) in rats found that caloric restriction prevents the age-related decline in mitochondrial oxidative capacity, thus preserving aerobic function in aged skeletal muscles. Caloric restriction also slows the loss of skeletal muscle and prevents the loss of muscle fibers, probably because of decreased production of reactive oxygen species and reduced mitochondrial abnormalities and dysfunction (11,67). Caloric restriction also attenuates the declines in function that occur with aging (83). Restricting calorie intake in animal models to 40-60% of an ad libitum diet, although maintaining adequate nutrient intake, has been shown to increase maximum life span by 30-40% (65,66). Caloric restriction also reduces the rate of decline in organ function and slows the onset of age-related diseases including diabetes, cancer, and Alzheimer's disease (57,113).

Although many may not find caloric restriction to be a palatable alternative to aging, there is a more attractive intervention worth consideration, a physically active lifestyle. Physical activity reduces risk for a variety of chronic diseases including coronary heart disease, diabetes mellitus, cancer (colon and breast), obesity, hypertension, bone and joint diseases (osteoporosis and osteoarthritis), and depression (25,112). Regular exercise is related to reduced morbidity (30) and mortality (78) in aging populations. It also contributes substantially to healthy aging by relieving symptoms of depression, helping to improve mobility and functioning, and maintaining independent living. Regular aerobic exercise improves arterial compliance (62), reduces systolic blood pressure, increases stroke volume and cardiac output, and increases glucose tolerance and insulin sensitivity (72,81). In addition, regular aerobic exercise of moderate intensity resulting in sufficient energy expenditure (200 kcal/d (78), or >1,000 kcal/wk (57)) reduces morbidity and all-cause mortality (72,81). Additional benefits have been documented with higher exercise intensities and expenditures.

A comprehensive exercise program includes aerobic work, resistance training that incorporates power training, flexibility exercise, and balance training. Such a program is a practical and relatively inexpensive weapon in the battle against chronic disease and age-related decline in functional performance. Resistance training has multiple positive effects on muscle mass and function, including enhanced MU recruitment, improved excitation-contraction coupling and calcium handling, and increased synthesis of contractile proteins (21). Other benefits include providing relief from arthritis pain, improving balance and reducing the risk of falling, strengthening bones, and reducing blood glucose levels (14,25).

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RESEARCH ON THE EFFECTS OF RESISTANCE TRAINING ON MUSCULAR STRENGTH, POWER, AND ENDURANCE IN OLDER ADULTS

Based on a meta-analysis, Hunter et al. (44) found that resistance training in older adults results in marked gains in muscle mass, strength, and power and functional improvements. In a review of 62 randomized controlled trials using progressive resistance training interventions, Latham at al. (55) found progressive resistance to have significant positive effects on leg extensor strength and some aspects of functional limitations, such as rising from a chair and gait speed; however, the effects disability were not clear.

Table 2 summarizes 28 studies designed to improve strength in older adults, (10,12,13,15,24,26,31,35,37-40,43,45,49,53,58,64,68,74,86,98,100,102-104,109,111), whereas Table 3 summarizes 11 studies focused on improving power (18,22,27,29,31,46,48,52,69,95,99). The majority of the research on resistance training for strength has included both men and women, although some studies have included only 1 sex (Table 2). Sample sizes have ranged from fewer than 10 to more than 100 participants (n = 109 (24); n = 113 (64)), with most having a total of approximately 20-40 (Table 2). Training studies typically have smaller sample sizes, and the subsequent limitation is being able to generalize the results to the population. The age of the participants in these samples ranges widely from 50 to 95 years, and most of these studies have included 60-to 80-year olds (Table 2). Studies vary quite a bit in the detail to which they report the health, disabilities, functional capacity, and other characteristics of the samples involved; however, the exercise prescriptions for strength do not vary based on the age of the participants and neither do those for power (Table 3). If anything, a justification is made for lower extremity exercise, particularly involving knee and hip extension, because lower extremity strength tends to show rather deleterious decrements with age. As the population ages, there is considerably more variability in health and function, and this is reflected in many of the samples of the studies reviewed.

Table 2

Table 2

Table 2

Table 2

Table 2

Table 2

Table 2

Table 2

Table 3

Table 3

Table 3

Table 3

Training frequencies of 1-3 days per week have been used, with 3 days per week being the most common by far, and training durations have ranged from 6 weeks (53) to 104 weeks or 2 years (10). The most common length for training programs is 12 weeks (9 of 28 studies; 10-12 weeks for 12 of 28 studies, Table 2). Training intensity varies considerably from 1 to 6 sets of 3-18 repetitions (reps) at 20-85% 1 repetition maximum (1RM); however, the most common combination appears to be 3 sets of 8 reps at 80% 1RM (Table 2).

Strength gains observed range from 5 to 174% across studies and vary across age ranges. The lowest strength gains were found in active women older than 60 years (74), whereas 2 of the greatest improvements in strength to date have been found in knee extensor strength in 10, 86- to 96-year-old men and women (174%) (26) and 11, 85- to 97-year-old men and women (40). Although most studies do not go into great detail regarding the health and functional status of the participants, it is safe to say that greater gains would be expected in deconditioned frail elderly with compromised functional status than those who are relatively active and whose function is not limited. In addition to gains in strength, 2 studies reported that resistance training resulted in improvements in muscular endurance (24,110), and 3 studies reported gains in functional fitness (10,24,100). Thus, resistance training has been shown to improve muscle strength, muscle endurance, and functional performance.

In a review of the effects of strength training on sarcopenia, Porter (84) indicated that earlier research on exercise for older adults emphasized low-intensity resistance exercise or endurance training and that this type of training did not result in significant gains in muscle mass or strength. More recent research has incorporated higher-intensity resistance training, and some studies have included both low- and high-intensity training. A review by Latham et al. (55) found that the effect size for 37 interventions using high-intensity resistance training was greater than that for 9 low-intensity interventions. Latham et al. (55) also found that studies of longer duration (>12 weeks) had a greater effect size than those of shorter duration (≤12 weeks). Four of 5 studies incorporating low- and high-intensity resistance training reviewed in this article (49,98,102,103,110) indicate that strength gains with high-intensity training are greater than those achieved with low intensity training (49,98,102,103) by approximately 15-20%. In summary, a dose-effect relationship exists between the intensity of resistance training and the strength gains achieved.

Lower-intensity strength training regimens (e.g., 20-50% 1RM) have the benefits of being more appropriate for those individuals who are apprehensive about starting a high-intensity resistance training program (e.g., 80% 1RM), promoting better adherence, reducing the risks of acute and overuse injuries, and for enhancing strength in the early phase of programs for individuals for whom heavy joint loading is contraindicated (e.g., individuals with osteoarthritis) (32). Both low- and high-intensity resistance training, 3 times per week, have been shown to reduce oxidative stress in older men (111) and may also mediate oxidative damage, antioxidant capacity, and mtDNA damage (47), that is, reducing factors associated with age-related declines in muscle function.

Fewer studies have involved strength and endurance training combined as compared with strength-only training (44). Hunter et al. noted that the results of these studies supported a synergistic effect of combined training on endurance performance compared with endurance-only training, as well as a synergistic effect on agility and dynamic balance performance. In a study comparing adaptations with strength-only and a combination strength and endurance training program in middle-aged adults, Häkkinen et al. (36) found similar strength development as measured by 3 lower extremity tests. However, only the strength-only training group achieved an increase in rate of force development during isometric knee extensions. Thus, the addition of endurance training to strength training in older individuals may limit improvements in important functional tasks that require rapid force generation, but an important consideration is that any functional improvement achieved is important (44).

The risk of disability can be greatly reduced, and functional independence can be enhanced in later life with the preservation of muscle power (23). Resistance training studies designed to improve power in older adults (Table 3) have used relatively small sample sizes of men and women from age 56 to 98 years, although the range of sample sizes is quite variable (n = 11-112). Training program duration has ranged from 8 to 16 weeks and has commonly involved 3 sessions per week of 3 sets of exercises, number of repetitions ranged from 4 to 15 (most in the neighborhood of 8-10 reps), and intensity has varied from 20 to 80% 1RM. In contrast to strength training protocols, power training protocols focus on explosive movements or exercises in which the concentric phase of the movement is performed as quickly as possible. Power has been assessed using a variety of exercises, including knee extension, leg press, half squat, stair climbing, vertical jump, arm pull, and bench press, and using isokinetic dynamometers and pneumatic resistance machines. However, most have focused on knee extension and leg press movements (59), and these exercises are most frequently used for training and testing. Training has elicited gains in power in all but one study (31), with improvements of 2-97%, most of which exceeded 20%.

In studies comparing strength and power training (29,52,69,95), results are consistent in that power gains have been significantly higher with power training. In one power study incorporating different levels of resistance, greater resistance (i.e., a higher percentage of 1RM) resulted in greater increases in force at peak power or FPP, and a dose-response effect was observed between intensity or percentage of 1RM and gains in FPP (19). Power training has also been found to be more effective than strength training in improving functional performance (69).

In a recent review of high-velocity power training in older adults, Sayers (96, p. 62) summarized the benefits of resistance training in older adults, stating that it “is essential to counter the age-related declines in muscle mass, strength and power that occur with aging”. Sayers (96) provided a convincing case for high-velocity power training over strength training for improving and retaining functional performance because power is more critical to functional tasks such as a chair rise and stair climb (6), or walking speed required to safely cross an intersection (91). Gains of 14-15% in peak muscle power have been achieved with high-velocity training at various percentages (i.e., 20, 50, and 80%) (19) of 1RM, and high-velocity power training at approximately 20% of 1RM resulted in the greatest improvement in balance in older adults compared with intensities of 50 and 80% of 1RM (77). The results from power training studies suggest that the speed of movement during power training rather than the intensity (i.e., percent 1RM) may be a critical variable in functional performance improvement (96). In addition, perceived exertion during high-velocity power training at 40% of 1RM seems to be lower than that of traditional strength training at 80% of 1RM (95), and lower perceived demand of the exercise is related to greater exercise adherence to or compliance with a resistance training protocol. More research is needed to determine the optimal determinants of compliance with resistance training protocols in older adults (96).

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RESISTANCE TRAINING PRESCRIPTION FOR OLDER ADULTS

Resistance training has multiple antiaging benefits. It helps maintain muscle mass and strength as one ages and can induce muscle fiber hypertrophy (27,97) and increase strength (15,31) in older individuals. In addition, the greater one's peak muscle mass, the less one is likely to experience disability (reduced functional capacity) because of sarcopenia in older age (61). Resistance training also increases oxidative capacity in older individuals (80). Resistance training thereby serves as not only an effective but also a potent countermeasure for skeletal muscle aging (47). What are the recommendations from the literature regarding using resistance training to achieve these benefits in older adults?

Hunter et al. (44) reviewed earlier studies using resistance training in older adults and found no consensus regarding the optimal training program. In the studies reviewed in this article, exercise prescriptions vary considerably. The most common prescription for strength training is 3 sets of 8 reps at 80% 1RM, 3 days per week for 12 weeks (Table 2). The exercise prescription for improving power frequently involves 3 sets of 8-12 reps at 50-80% of 1RM with an emphasis on high-velocity concentric contractions or explosive movements (Table 3). Neither prescription appears to be based solely on the age of the participants in the research studies reviewed because fitness levels and functional status tend to be more variable with increasing age.

Based on a fairly recent meta-analysis by Rhea et al. (89) and their own review of the literature, Hunter et al. (44) offered the following guidelines for resistance exercise prescription, which are on the more rigorous end of the spectrum: 2-4 sets of 8-15 reps at 60-80% of 1RM, 2-3 days per week. In contrast, the exercise prescription for resistance training given in recent recommendations for physical activity and public health in older adults by the American College of Sports Medicine (ACSM) and the American Heart Association (AHA) (72) and that in the newly revised ACSM's Guidelines for Exercise Testing and Prescription (2) are perhaps the most conservative of those found in the literature for older adults. These guidelines endorse at least 1 set of 10-15 reps at a moderate-intensity effort (5-6 on a 10-point effort scale) of 8-10 exercises using all major muscle groups, at least 2 days per week, 48 hours apart or on nonconsecutive days. Stair climbing and other strengthening activities can be incorporated into a progressive program of weight training or weight-bearing calisthenics (2). This prescription is aimed toward improving muscular fitness, that is, both strength and endurance, as do other prescriptions found in the research (Table 2). The primary focus of resistance training prescriptions seems to be weighted more toward strength, and although gains in both strength and endurance may be desirable, if endurance-focused training is added to strength training, it should be performed no more than 3 days per week (44).

Galvão and Taaffe (32) have recommended that volume and training frequency be prescribed to provide a sufficient stimulus for the desired outcomes without exacerbating injury or pain, and consideration should be given to training frequency and volume, so as not to have a negative impact on the participant's enjoyment of the exercise session and training program and, thus, reduce adherence. Their prescription offers a bit more flexibility than that of ACSM and AHA (72). More specifically, Galvão and Taaffe (32) recommend incorporating resistance training into the activities of older adults at least once a week, with 1-3 sets at 40-50% 1RM, performed at variable speeds (i.e., some higher-velocity work at least once a week). The recommendation for 1-3 sets is based on that fact that multiple sets may not be necessary for significant strength gains given that many older adults may be in a detrained state to begin with. The lower intensity (40-50% 1RM) is based on similar strength gains achieved with lower or higher percentages of 1RM as long as training volume is similar. Also, lower-intensity exercise tends to be associated with a reduced risk of injury and greater exercise adherence. The inclusion of explosive or higher-velocity training is geared toward power development and related improvements in functional status (32,54).

It should also be noted that the principle of progressive overload has been used in a number of studies of resistance training in older adults (68,100,110), with regular 1RM assessments and adjustments of the training intensity to continue to obtain strength or power gains over time. A recent position stand provided by the ACSM (87) on progression models in resistance training for healthy adults indicates that the optimal resistance training prescription include concentric, eccentric, and isometric muscle actions and bilateral and unilateral single and multijoint exercises. This position stand also indicates that the exercise prescription should be tailored to the client's level of training and experience with resistance training, as well as his/her physical capacity and goals. Frequency, intensity (sets, reps, percent 1RM, work-rest ratios) and the rate of progression vary depending on all of these factors.

It is clear from the literature that the prescription for resistance training in older adults varies considerably, as it should. The exercise professional must consider the individuals for whom exercise is being prescribed - their level of deconditioning or fitness, familiarity with resistance training, and any special needs or functional limitations (arthritis, injury, pain, balance issues, etc) - to incorporate an appropriate frequency, intensity, duration, and mode. Including some low-intensity (e.g., 40% 1RM) high-velocity training to enhance muscular power is frequently advised to improve functional performance (32,45,54). A variable intensity prescription might be used for those with advanced sarcopenia and/or elderly women to increase recuperation between high-intensity bouts. Resistance training can also be used effectively with individuals affected by arthritis (82), and the intensity of the exercise prescription is different for those in the acute arthritic stage versus the chronic stage (82).

With regard to how to work effectively with and prescribe a safe resistance training program for older adults, Mahady (60, pp. 4-5) has offered numerous guidelines for the exercise professional. He extols the use of machines over free weights with older adults for the mode of exercise because machines require less skill to use, provide more back support by stabilizing body position, generally allow lower levels of resistance, and enable increased resistance levels through small increments (for progressive overload). In addition, machines allow greater control of the range of motion during exercise and provide a more efficient workout (60).

Although the use of weight machines may be an appropriate starting point in a progressive resistance training program for deconditioned or frail elders, or individuals with balance issues, potential gains in core strength and stability as well as balance improvements are likely to be limited compared with those that could be achieved with multijoint and multiplanar movements using free weights and with power training. In addition, it should be noted that less-expensive alternatives to weight machines and weights have been effectively used to improve both strength and power. Fahlman et al. (24) used Thera-Bands to improve upper-body strength, endurance, and overall function in older men and women (mean age approximately 75 years) with limited functional ability; and Skelton et al. (99) used elastic tubing and rice bags with adults from 76 to 93 years of age to achieve an 18% (but nonsignificant) improvement in lower limb power. A variety of exercise equipment and modes can be used to effect improvements in fitness and function.

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RESEARCH ON MOBILITY, BALANCE, AND RISK FOR FALLS

Of the risk factors for limited mobility and falls in the elderly, impaired balance and gait are the 2 most significant (17). Reduced muscle mass and strength are associated with increased frailty, an increased risk of falls, and eventual functional limitations. Mobility problems may lead to falls, which in turn may result in hip fractures. After age 50, the risk of hip fractures increases, and many individuals who experience a hip fracture do not survive the first year postfracture or do not regain the ability to walk without assistance, which leads to institutionalization. Maintenance of mobility is central to the issues of independence and quality of life in the later years of life.

Balance is reduced in older adults as indicated by more pronounced postural sway, with 50% of older adults sufficiently destabilized to need assistance with balancing (17). In addition, stride length and walking speed are reduced, significantly reducing walking efficiency. These balance and gait impairments, coupled with reductions in muscular strength and particularly power, result in diminished ability to cope with environmental hazards and balance perturbations, leading to falls.

The risk of falls increases by 35-40% in individuals older than 60 years and is greater in women. Falling is the leading cause of fatal injury in adults older than 70 years. Fall risk is increased with arthritis; orthostasis; impairment in muscle strength, cognition, vision, balance, or gait; depressive symptoms; and the use of 4 or more prescription medications (107) and as the number of risk factors increase, the risk of falling increases (73,108). The U.S. Preventive Services Task Force has recommended that all individuals of 75 years and older and those of 70-74 years of age who have a risk factor for falling be counseled about specific measures to prevent falls (85). The Task Force has also recommended that elderly individuals who are at high risk of falling receive individualized multifactorial interventions in settings in which adequate resources are present to deliver such services.

Several prospective, randomized, controlled studies of physical activity and fall risk have been done on older adults (aged 60+ years) with durations of 2-12 months that resulted in reductions in fall risk of roughly 15 or 20-40% (51). Interventions have involved home-based balance and strength training; combinations of resistance training, endurance training, flexibility training, and balance training, including Tai Chi (114); and water walking and deep water running (50). Tai Chi training has been shown to reduce response time and co-contraction of antagonistic muscles and improve performance on 4 clinical measures of functional balance. Tai Chi training also resulted in reduced tripping and increased step length and mechanical loading at the hip when stepping onto an unstable surface, which may suggest greater confidence and self-efficacy (33). In contrast, other prospective, randomized, controlled studies of physical activity and fall risk have not shown a reduction in fall risk, and some studies suggest that more active individuals are at greater risk for falling (51). It seems that physical activity alone does not reduce fall risk but that combination programs involving resistance training, flexibility training, and/or some type of balance training are the ticket.

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RESISTANCE TRAINING PRESCRIPTION FOR BALANCE, MOBILITY, AND REDUCED FALL RISK

To prevent falls, the ACSM and AHA (72) recommend that community-dwelling older adults with substantial risk for falls perform activities that maintain or improve balance. ACSM's most recent recommendations for frequent fallers or individuals with mobility problems include 2-3 days per week of neuromuscular training, which combines balance, agility, and proprioceptive training (2). “General recommendations include using (a) progressively difficulty postures that gradually reduce the base of support (e.g., two-legged stand, semitandem stand, tandem stand, and one-legged stand); (b) Dynamic movements that perturb the center of gravity (e.g., tandem walk and circle turns); (c) stressing postural muscle groups (e.g., heel stands and toe stands); (d) reducing sensory input (e.g., standing with eyes closed); and (3) tai chi”" (2, pp. 193-194). However, no specific prescription is given for intensity, duration, or mode of exercise. It appears that more research is needed to establish an optimal or at least effective exercise prescription with regard to improving balance and mobility and reducing risk for falls.

At least 1 group of researchers has attempted to provide a more specific prescription for these aspects of fitness. Oddsson et al. (76) recommend balance training that incorporates exercises to maintain voluntary control of balance (using balance balls, balance disks, or other tools), perturbation exercises that focus on recovering balance, and dual-task exercises (that include a cognitive challenge) to improve balance control. Sessions should “constantly challenge the postural control system with exercises that incorporate elements related to the demands of normal activities of daily living” (76, p. 18). Oddsson et al. (76) recommend 5 levels of exercise to be incorporated in a balance training program: (a) sitting and standing exercises with external support; (b) sitting exercises without external support; (c) standing exercises including double leg stance and no external support; (d) standing exercises including single leg stance, gait, and no external support; and (e) perturbation exercises, reactive and proactive responses. This type of program has been shown to result in improvements in functional status and postural control variables (9). If done in a group exercise format, a dynamic atmosphere favorable to socialization can be established and promoted.

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PRESCRIPTION FOR FLEXIBILITY

Recommendations from ACSM and AHA for older adults (72) include flexibility training on at least 2 days per week for at least 10 minutes per day, using static stretches of 10-30 seconds in duration and performing 3-4 repetitions per stretch, involving all major muscle groups. More recent guidelines from ACSM recommend the same frequency of stretching, with moderate-intensity (5-6 on a scale of 0-10), and incorporating “any activities that maintain or increase flexibility using sustained stretches for each major muscle group and static rather than ballistic movements”"(2, p. 193). Flexibility exercises can be done on the same days as resistance training and aerobic training as part of the cool-down portion of a workout. Flexibility training provides a nice complement to resistance training by balancing the emphasis on muscle shortening in lifting with stretching and lengthening. Flexibility exercise also helps to counteract the stiffening of joints and postural changes (i.e., kyphosis) that occur with aging and may contribute to better function and, therefore, quality of life.

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PRESCRIPTION FOR CARDIORESPIRATORY ENDURANCE

To promote and maintain health, ACSM and AHA (72) recommend that older adults perform moderate-intensity aerobic activity for at least 30minutes, 5 days per week, or at least 20 minutes of vigorous-intensity aerobic activity, 3 days per week; or some combination of moderate-and vigorous-intensity activity 3-5 days per week. The more recent ACSM guidelines for exercise for aerobic fitness add that the moderate-intensity activities can be done for up to 60 minutes per day for greater benefit, in bouts of at least 10 minutes each to total 150-300 minutes per week or at least 20-30 minutes per day of more vigorous-intensity activities to total 75-100 minutes per week or an equivalent combination of moderate- and vigorous-intensity activity (2). This activity is in addition to routine ADLs of light- and moderate-intensity of 10 minutes duration or less. Initially, deconditioned or inactive older adults can approach these levels of activity gradually using multiple bouts of activity lasting 10 minutes or more in duration (2). There are benefits from lower levels of activity even if older adults do not meet prescribed guidelines. Something is better than nothing!

Additional information regarding exercise prescription for older adults and that more specific to chronic conditions and disability can be found in review articles (28,63,75), although the guidelines for resistance training provided therein are based at least in part on less recent research.

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STRATEGIES FOR AGING WELL-SUMMARY AND RECOMMENDATIONS

Aging is associated with great potential for significant changes in structure and concomitant declines in function, often accompanied by chronic conditions, which can have detrimental effects on our quality of life. As life expectancy increases and older adults make up a growing percentage of the population, our need to understand the factors that increase health and vitality increases (106) in order to maintain quality of life. Research has provided us with strategies for slowing the rate of aging, improving functional performance, and enhancing quality of life. One of the most potent and inexpensive of these is exercise.

“The old adage ‘use it or lose it’ is a key rule for maintaining physical independence as a person grows older” (88, p. 93). A comprehensive physical activity program for older adults includes aerobic exercise, resistance training including power training, neuromuscular training, and flexibility exercise. One component in particular, resistance training, is associated with a long list of documented benefits, including increased muscle mass and strength, and enhancements in functional performance (particularly with power training), which is related to being able to maintain independence and protect quality of life. Thus, resistance training programs designed to improve strength and power hold great promise for helping us age well. The potential benefits to society are the reduced health care burdens posed by individuals with declining physical function and the maintenance of an underappreciated community resource, our elderly.

The exercise professional who is familiar with age-related changes and challenges that face older adults is poised to assist them in aging well by helping them to improve their fitness, particularly muscular fitness. Muscular strength, power, and endurance have significant implications for physical function and quality of life. As prescriptions for resistance training vary among studies and as older adults vary considerably in health, fitness, and functional status; the exercise professional will need to carefully consider the exercise prescription. What will best suit his/her older clients in terms of their baseline levels of fitness and function and their goals, and what can be done safely to assist clients in their achievement are key to individualizing exercise prescription. In addition, armed with this knowledge of the benefits of resistance training and knowing from the research the types of prescriptions that have yielded gains in fitness and function, we can all take steps to age successfully.

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                  Keywords:

                  age-related changes; strength training; power training; functional performance

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