Resistance Exercise to Prevent and Manage Sarcopenia and Dynapenia

Abstract

For well over twenty centuries the muscle wasting and weakness that occurs with old age has been a predominant concern of mankind. As eloquently reviewed by Narici and Maffulli (Narici & Maffulli, 2010), the Classic Greeks (4^th and 5^th centuries BC) detested the degrading effects of aging on their bodies and considered it a chronic, incurable, and progressive disease. However, by the 1^st century BC and the 1^st century AD the perspective on physical frailty and aging started to change as Cicero and others began to view aging not as an irreversible illness, but rather a modifiable condition. In fact, in his ‘Essay on Old Age’ in 44 BC Cicero argues that ‘it is our duty… to resist old age, to compensate for its defects, to fight against it as we would fight a disease; to adopt a regimen of health; to practice moderate exercise; and to take just enough food and drink to restore our strength’. While Cicero’s suggestion to use exercise to combat muscle wasting and weakness was logical, it did not truly gain steam in the scientific and medical communities until the latter part of the 20^th century. In particular, a series of landmark studies published in the early 1990’s by Fiatarone and colleagues in the Journal of the American Medical Association (Fiatarone et al., 1990) and the New England Journal of Medicine (Fiatarone et al., 1994) highlighted the profound role that progressive resistance exercise training¹ (RET) can have on increasing muscle strength, muscle size and functional capacity in older adults. For instance, the first of these studies demonstrated that institutionalized, nonagenarians (i.e., individuals from 90 to 99 years old) were able to increase their muscle strength, on average, an astounding 174%, their mid-thigh muscle area 9.0%, and their gait speed 48% with 8-weeks of high-intensity progressive RET (Fiatarone et al., 1990). By the start of the 21^st century we knew that muscle fiber types of older adults were able to hypertrophy (~30% increase in size with 16 weeks of high-intensity RET), transition their fiber type (from type IIX fibers to IIA), and had the capacity to incorporate new nuclei into the fibers (Hikida et al., 2000). These adaptations are comparable to what is observed in younger individuals suggesting that the muscle of older adults is not limited in its ability to adapt. Some two decades later, there is now evidence indicating that high-intensity RET, when coupled with other targeted multidisciplinary interventions, results in lower mortality, nursing home admissions, and disability compared with usual care after hip fracture (Singh et al., 2012).

With the demographic profile of the United States, and the world for that matter, changing (e.g., more than 14% of the entire U.S population is now greater than 65 years (Bureau, 2015)) there is a continued and growing interest in developing effective interventional strategies to combat muscle wasting and weakness associated with aging. To date, the scientific evidence suggests that high-intensity, progressive RET (also commonly referred to as ‘strength training’) is one of, if not the most, effective interventional strategies to enhance muscle size and strength in the elderly (Bird, Hill, Ball, & Williams, 2009; Chale et al., 2013; Charette et al., 1991; Fiatarone et al., 1990; Fiatarone et al., 1994; Hikida et al., 2000; Kalapotharakos, Diamantopoulos, & Tokmakidis, 2010; Liu & Latham, 2009; T. Manini et al., 2007; Sylliaas, Brovold, Wyller, & Bergland, 2011; Van Roie, Delecluse, Coudyzer, Boonen, & Bautmans, 2013). Accordingly, in this article we will briefly review the current literature regarding the use of RET to prevent and manage sarcopenia and dynapenia, and provide pragmatic advice for patients and practitioners on the resistance exercise prescription for older adults. First, however, we will discuss sarcopenia and dynapenia with special attention on their operational definitions.

Sarcopenia is a term, originally proposed by Rosenberg in 1989 (Rosenberg, 1989), specifically referring to the loss of muscle mass associated with ageing. However, the meaning of this term has often been extended to the age-related loss of muscle strength and/or physical function. Although sarcopenia is certainly a contributor to muscle weakness, it has been argued that these two terms should not be used interchangeably since this would imply a direct proportionality between the two (Clark & Manini, 2008; T. M. Manini & Clark, 2011; T.M. Manini, Russ, & Clark, 2012; Narici & Maffulli, 2010; Visser & Schaap, 2011), which is not the case as a variety of other neural and muscular factors contribute to force output that are independent of muscle mass (For review see: (Clark & Manini, 2008; Duchateau & Enoka, 2002; T. M. Manini & Clark, 2011; T.M. Manini et al., 2012; Narici & Maffulli, 2010)). Accordingly, the term dynapenia was proposed by Clark and Manini in 2008 to specifically refer to the loss of muscle strength and power associated with aging (Clark & Manini, 2008).

While there are semantic debates in the literature, there is progress towards developing criteria/criterion for the diagnosis of clinically significant sarcopenia and/or dynapenia in recent years. For example, the European Working Group on Sarcopenia in Older People incorporates aspects of 1) physical function (i.e., gait speed), 2) muscle strength, and 3) muscle mass into a singular diagnosis of sarcopenia (Cruz-Jentoft et al., 2010). Other criteria, namely those by the Foundation for the National Institutes of Health’s Sarcopenia Working Group, attempted to define low muscle mass and muscle weakness independently using a data driven approach in a pooled sample of 26,635 older adults (Studenski et al., 2014). While there are significant efforts being put forth by both researchers and practitioners in the development of diagnostic criteria, it is important to note there are no established agreed upon definition for these common conditions at this time.

RET and the Management and Prevention of Muscle Wasting and Weakness

While sarcopenia and dynapenia are realized to be major clinical problems for older adults, until recently there has been little wide spread support for ways to combat these debilitating conditions. However, research on the effects of exercise and nutrition on sarcopenia and dynapenia has rapidly expanded in the past one to two decades (Sayer et al., 2013). Today, there is still limited evidence suggesting that pharmacologic interventions effectively ameliorate sarcopenia and/or dynapenia. However, there is strong and growing evidence that progressive RET can combat both sarcopenia and dynapenia (Burton & Sumukadas, 2010), as RET has a profound effect on virtually all of the physiological mechanisms in the nervous system and the muscular system known to influence strength (Duchateau & Enoka, 2002; Russ, Gregg-Cornell, Conaway, & Clark, 2012). For instance, maximal motor unit discharge rates, a key ‘neural factor’ involved in muscle strength, increased 49% in older adults following only 6-weeks of high-intensity progressive RET (Kamen & Knight, 2004). Non-mass dependent muscular factors, such as muscle fiber fascicle length and tendon stiffness, have also been observed to increase (10% and 64%, respectively) following RET in older adults 64%, respectively (Reeves, Maganaris, & Narici, 2003). Additionally, RET is also a powerful stimulus for inducing muscle hypertrophy as illustrated by 24-weeks of RET, when coupled with modest protein supplementation, increasing thigh muscle cross-sectional area 4.6% in mobility limited older adults (Chale et al., 2013). Given that there exists widespread evidence that inactivity, which is prevalent in the elderly (Troiano et al., 2008), leads to loss of muscle mass and strength (Clark, 2009), findings of this nature would (or should) lead all scientists and clinicians to support the use of RET for treating, slowing, and/or preventing sarcopenia and dynapenia.

Indeed, the extant literature supports this notion. For instance, a 2009 Cochrane review of 121 trials including over 6,700 participants concluded that ‘progressive resistance training is an effective intervention for improving physical functioning in older people, including improving strength and the performance of some simple and complex activities’ (Liu & Latham, 2009). Most of the trials reviewed involved high intensity training two to three times per week. Benefits included large positive effects on both muscle mass (hypertrophy) and strength (Liu & Latham, 2009). A functional assessment of gait speed showed a modest improvement and a strong effect was observed on the ability to rise from a chair (Liu & Latham, 2009).

It is well recognized that the effectiveness of RET for strength and muscle mass improvement is variable across studies, and recent meta-analyses by Peterson and colleagues attempted to identify critical aspects of RET programs which promote strength adaptation (e.g., the frequency of exercise training, the duration of exercise training, the intensity of exercise training, the volume of exercise training, etc.) (Peterson, Rhea, Sen, & Gordon, 2010; Peterson, Sen, & Gordon, 2011). These studies revealed two critical aspects for positive adaptations associated with progressive RET. First, higher intensity RET is associated with greater improvements in muscle strength. Specifically, with each incremental increase in exercise intensity from low intensity (<60% of 1-repetition maximum or 1-RM), low/moderate intensity (60–69% of 1-RM), moderate/high intensity (70–79% of 1-RM) to high-intensity (≥80% of 1-RM) the average percent change in strength was 5.3% (Figure 1A) (Peterson et al., 2010). Second, higher RET volume, defined as the total number of exercise sets performed per session, is associated with greater improvements in lean body mass after controlling for a variety of confounders (e.g., age, study duration, gender, training intensity and frequency, etc.) (Figure 1B) (Peterson et al., 2011). This finding suggests that for every additional 10 sets of exercise performed per session that one can expect, on average a 0.5 kg increase in lean body mass (Peterson et al., 2011). It should be noted that this study reported the older individuals experienced a lesser increase in LBM with RET (Peterson et al., 2011). Some scientists have suggested that there are “non-responders” to progressive RET (Bamman, Petrella, Kim, Mayhew, & Cross, 2007); however, a recent retrospective analysis revealed that, while there is a large heterogeneity in the adaptive response to prolonged RET as it relates to changes in strength and mass, the level of responsiveness was strongly affected by the duration of the exercise intervention, with more positive responses following more prolonged exercise training (Churchward-Venne et al., 2015). Accordingly, these findings suggest that there are no true “non-responders” to the benefits of RET amongst the elderly and that it should be promoted without restriction to prevent and manage sarcopenia and dynapenia. In figure 2 we present conceptual interactions between physical activity, sarcopenia, dynapenia, fatigability, exercise tolerance, and physical function (Figure 2A) and how progressive resistance exercise training can modulate these various phenotypic factors (Figure 2B).

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Figure 1

Higher intensity resistance exercise training is associated with greater improvements in muscle strength (Figure 1A), and higher volume resistance exercise training is associated with greater improvements in lean body mass (LBM) (Figure 1B)

Figure 1A: Peterson et al. reported in a meta-analysis that with each incremental increase in exercise intensity from low intensity (<60% of 1-RM), low/moderate intensity (60–69% of 1-RM), moderate/high intensity (70–79% of 1-RM) to high-intensity (≥80% of 1-RM) training the average percent change in strength was 5.3% (Peterson et al., 2010). Figure 1B: LBM change by training volume (defined as sets per session) when weighted by the number of subjects in a given study using a meta analytical approach (Peterson et al., 2011).

Figure 1A was created from data presented in Peterson et al., Resistance exercise for muscular strength in older adults: a meta-analysis. Ageing Research Reviews, 226–237, 2010. Figure 1B was reprinted with permission by Peterson et al., Influence of resistance exercise on lean body mass in aging adults: a meta-analysis. Med Sci Sports Exerc, 43: 249–258, 2011.

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Figure 2

Conceptual interactions between physical activity, sarcopenia, dynapenia, fatigability, exercise tolerance, and physical function (2A) and how progressive resistance exercise training can modulate these various phenotypic factors (2B)

Note that other influences, such as nutritional, cognitive, and psychological factors, are not shown for clarity.

Adapted with permission from Liu and Fielding. Exercise as an intervention for frailty. Clin Geriatr Med. 27:101–10, 2011.

The Common Practices Are Not the Best Practices

Unfortunately, many older people are unable or unwilling to embark on strenuous exercise training programs, and, despite a call from the American Academy of Family Physicians (Physicians, 2015), many seniors are often prescribed “low dose” resistance exercise programs that are physiologically inadequate to increase gains in muscle mass and strength. In 2004, the National Council on Aging (NCOA) Center for Healthy Aging released a guide entitled “Best Practices in Physical Activity” in order to disseminate information to the public regarding the best-practice and evidence-based models which were being employed at a community level (local public or non-profit organizations) to facilitate older adults in achieving and maintaining functional independence and vitality (NCOA, 2004). A team of experts developed best-practice criteria based on expert opinion and findings from the literature and identified 10 community-based programs as national best-practice programs. In 2009, Hughes et al. assessed the impact of these 10 best-practice physical activity programs for older adults in terms of health related outcomes (Hughes, Seymour, Campbell, Whitelaw, & Bazzarre, 2009). Not surprisingly, these community-based physical activity programs, which utilized multiple-component physical activity interventions, measurably improved aspects of physical function that are risk factors for disability among older adults. Unfortunately, our anecdotal observation is that there is a large degree of variability in the implementation of physical activity programs in the community-based setting. Common barriers to implementation and participation in community-based exercise programs are program costs, lack of transportation/accessibility, lack of necessary time commitment, unsupportive physical environments, psychological barriers with regards to negative connotations of exercising in the older adults, as well as lack of expertise (Mathews et al., 2010, Boyette et al., 2002, Schutzer et al., 2004). In 2009, Cress et al. identified the key components of best practice physical activity programs for older adult populations as being 1) muscular strength and endurance, 2) balance, 3) cardiovascular endurance, and 4) flexibility (Cress et al., 2005). While many of the existing best practice community programs incorporate these components into their physical activity interventions, very few have adopted the American College of Sports Medicine (ACSM) guidelines for progressive high intensity RET to promote muscle hypertrophy, strength and power (American College of Sports, 2009). An example of one such program is the National Institute on Aging’s Go4Life program (NIA, 2015). While this program encourages older adults to create personal physical activity programs incorporating all four of these key components, the examples provided for muscular strength training/resistance exercises on the Go4Life website are very low to moderate intensity exercises for most seniors and are difficult to progress as they utilize wrist weights, TheraBand™, small hand weights, and gravity-reduced body weight resistance exercises. Similarly, our observations indicate that many rehabilitation facilities (including hospitals, short-term and long-term stay facilities) have not adopted high-intensity progressive RET into their standard protocol for the pre-frail and frail elderly client/patient populations. While many of these facilities offer 60 minutes of therapy twice per day, they commonly use low intensity exercise (e.g., seated in a wheelchair performing knee extension exercises with ankle weights) in conjunction with some functional training (i.e., wheelchair transfers), and aerobic activity. While the types of exercises mentioned above present adequate entry-level exercises for seniors, they are not likely a sufficient stimulus to promote positive muscle growth and adaptation. Accordingly, in the following section we attempt to provide pragmatic resistance exercise advice for patients and practitioners.

Pragmatic Resistance Exercise Advice for Patients and the Practitioner

When developing RET programs for older adults it is important to consider all of the various training-related variables, such as, frequency, duration, exercises, sets, intensity, repetitions, and progression. Also, many older adults often have existing health issues (e.g., orthopedic limitations, cardiovascular disease, etc.) that require special consideration. The Exercise And Screening for You (EASY) survey is a tool that helps provide guidance on appropriate exercise programs for seniors (Program on Healthy Aging, 2008). It is also suggested that older adults who are beginning a RET program receive proper instruction and supervision by an appropriately trained exercise professional, such as a physical therapist or an exercise physiologist.

RET Repetitions

Repetitions refer to the number of times an individual performs a complete movement of a given exercise. The number of repetitions that one can perform is inversely related to the exercise intensity (i.e., the higher the intensity the fewer repetitions that can be performed). As illustrated in Figure 3, if an individual is exercising at 60% of his/her maximum strength, he/she will likely be able to perform between 18–32 repetitions to “task failure” using free weights. At 80% of the individual’s maximum strength, the number of repetitions to failure is generally between 8–15, and at 90% it is 4–12 repetitions with free weights. The number of repetitions to failure for machines is, generally speaking, slightly higher than with free weights (Figure 3) presumably due to free weights requiring more muscles for stabilization and balance compared to a fixed path machine lifting task. Understanding these relationships is important, as it provides a mechanism for a trial-and-error approach to be utilized to prescribe the appropriate training load without having to actually test muscle strength (e.g., performing the exercise to task failure within 10–15 repetitions would likely indicate that an individual is exercising at an intensity in the 70–85% of maximum strength range).

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Figure 3

Relationship between the number of repetitions untrained (3A) and trained (3B) healthy adults were able to perform using free weights at four different resistance exercise intensities (60, 80 and 90% of 1-RM) for the squat (square), bench press (triangle), and arm curl (circle). Relationship between the number of repetitions untrained (3C) and trained (3D) healthy adults were able to perform using resistance exercise machines at three different resistance exercise intensities (60, 80 and 1-RM) for the leg press (square), chest press (triangle), and arm curl (circle). Data represents the mean response for each exercise and intensity, respectively.

Figure 3A and 3B created from data presented in Shimano et al., Relationship between the number of repetitions and selected percentages of one repetition maximum in free weight exercises in trained and untrained men. J Strength and Conditioning Research. 20: 819–823, 2006.

Figure 3C and 3D created from data presented in Hoeger et al., Relationship between repetitions and selected percentages of one repetition maximum: a comparison between untrained and trained males and females. J Applied Sport Science Research. 4: 47–54, 1990.

Conclusions

A well-designed, progressive resistance exercise training program is well known to exert positive effects on both the nervous and muscular systems and, ultimately, results in profound enhancements in muscle mass and muscle strength. Accordingly, resistance exercise training should be considered a first-line treatment strategy for managing and preventing both sarcopenia and dynapenia. While there are many components to an optimal resistance exercise prescription, exercise intensity, exercise volume and progression, are critical factors that deserve strong consideration as it relates to following best practice guidelines. We hope the example resistance exercise training program presented herein is useful for academicians, students, and health care providers across a variety of disciplines, including those in the long term care industry.

Acknowledgments

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