BACKGROUND
During the past three decades, it has become increasingly more evident that resistance training must be an integral part of any exercise program designed to increase independence and reduce fall probability in older persons (10,12). Throughout the aging process, the size and quality of skeletal muscle decline. These declines are one of the major factors associated with reduced strength, power, endurance, and contractile speed and may vary in severity depending on the unique impacts of environment and genetics on each person’s aging process.
Initially, the studies that examined resistance training concentrated on hypertrophy-based programs that addressed the most obvious problem associated with skeletal muscle, sarcopenia. “Sarcopenia” is defined as muscle mass lower than 2 SDs from the mean of healthy 20-year-olds. In more concrete terms, this translates into muscle mass that is lower than 97.5% of the population. It has been estimated that from age 60 to 80 years, the prevalence of sarcopenia in the general population progresses exponentially from 15% to 32% for men and from 23% to 36% for women. After the age of 80 years, these values increase to about 51% for women and 55% for men. For this reason, the programs most often used during these early studies, even those which measured strength as a dependent variable, were hypertrophy based.
THE TRAINING CONTINUUM AND BEYOND
As researchers and practitioners have explored the use of resistance training as an intervention to reduce the impact of aging on performance, they progressively applied training concepts that have been used for years in the training of younger individuals. One such concept is the training continuum. Simply defined, the “training continuum” is a template for the patterns of change in load, volume, and work/recovery cycle that allows the targeting of strength, hypertrophy, and endurance. In addition, factors such as contractile speed and lifting patterns can be superimposed within this continuum to focus on additional elements including power and body composition. Figure 1 provides a modified training continuum illustrating the use of high-speed contractions to allow increases in power along the training continuum. The figure also shows that high-speed movements can be added to a hypertrophy-based program to affect positive changes in body composition. This article summarizes the latest findings in the literature as they relate to two interactive concepts: the training continuum and an assessment/prescription model for targeted resistance training. The details for specific goals will be presented in the sections on Hypertrophy, Strength, Power, Endurance, and Body Composition.
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FigureFigure 1: A diagram of a modified resistance training continuum showing specific goals in bold print with load, volume, and recovery suggestions. Also included are the suggestions for superimposing power- and body composition-based interventions on the traditional continuum. Loads and recoveries modified from Campos
et al. (
5).
THE ASSESSMENT/PRESCRIPTION MODEL
The American College of Sports Medicine’s (ACSM’s) Exercise is Medicine® initiative continues to make headway as physical activity takes its warranted position as an intervention to improve health and well-being. The term “exercise prescription” is evolving to reflect the more practical definition that has been used by the medical community. Just as a physician would not think of providing a prescription without first diagnosing the patient’s needs, so the wellness professional should assess needs before offering a training prescription. As it relates to resistance training, the theory of exercise specificity states that the structural and operational changes made by the neuromuscular system in response to a training overload will reflect the nature of the overload; therefore, the exercise prescription provided to the older person should reflect his or her assessed limitations.
Each section of this article will provide testing methods and training caveats based on the needs of the individual. Two principles should be remembered when considering the conceptual framework underlying the use of the assessment/prescription model. The first is that each individual will have his or her own specific needs, which will dictate the training pattern to be used at the onset of training. This is illustrated in Figure 2, which shows the performances of a number of subjects on two different tests, the 8-ft up-and-go and the gallon jug shelf test. The results illustrate a number of important concepts. As can be seen by examining the positions of the subject numbers as they relate to the trend line, using age as the sole factor in prescribing a training protocol would be moderately effective at best. In addition, by examining the positions of specific subjects above or below the trend line, it can be seen that an individual who demonstrates above-average performance on one test may perform below average on another.
Figure 2: Performance times for subjects aged 18 to 85 years on (A) the gallon jug shelf test and (B) the 8-ft up-and-go test. (Adapted from: Signorile JF. Bending the Aging Curve: The Complete Exercise Guide for Older Adults. Champaign (IL): Human Kinetics Publishers; 2011, pp. 24–26.)
The second concept is that each person will have his or her unique pattern of adaptation to a specific training overload. Remember that the theory of specificity states that an individual who is being trained is an evolving entity who will change in accordance to the overload provided. However, each person has a unique genetic code and life experience that will cause him or her to respond differently to the same training. For this reason, testing should not be limited to the beginning of the training period but should be included at regular intervals so that the training prescription can be modified to optimize benefits.
TESTING
Strength
A number of tests are available to assess specific neuromuscular performance variables, and most provide normative values conditional to the age group and sex of the person being evaluated. For strength, the most commonly used assessment is maximal grip strength. Although grip strength has been shown to be a strong predictor of independence, its use as an assessment tool to target training is limited by the fact that it evaluates only hand strength. Fortunately, isometric, isokinetic, and isoinertial tests and norms are available to assess other muscle groups important to older persons’ well-being (3,13,21). The efficacy of isometric testing is often questioned because of the need for specialized and often costly instruments and the reported lack of correlation between isometrics and dynamic performance. While isokinetic testing allows the assessment of strength in a velocity-controlled environment, the same criticisms concerning cost and applicability of results to daily performance once again limit its relevance. Although 1 RM (repetition maximum) testing is the gold standard for isoinertial strength assessment, because of the potential risks, ACSM recommends the use of submaximal tests and predictive equations. The tests most commonly used are the leg press, the leg extension, and the chest press. Predictive equations for the bench press and leg press exercises are provided with indications of correlations between predicted and actual 1 RM values in Sidebar 1. Concerning the bench press, strength also can be easily evaluated using the YMCA Bench Press Test (16). The 30-second chair stand and arm curl tests are field tests that allow the assessment of upper (biceps) and lower (quadriceps) body strengths, and although normative values are available by sex and age group, they cannot be used to compute 1 RM values (28).
Table: No title available.
Power
Power can be evaluated using isokinetic dynamometry and isoinertial testing, as well as specially designed rigs, such as the Nottingham rig. Each of these methods requires considerable cost because even the assessment of isoinertial power would require a machine with the capacity to monitor both load and movement speed. Fortunately, there are a number of field tests that can be used to assess lower body power. Sidebar 2 provides equations for the stair climb, ramp climb, and 20-second chair stand tests. In addition, movement speed can be evaluated using both usual and maximum gait speed (23). Given the progressive increase in grade from the gait tests through the 20-second chair stand, these tests allow analysis of power along the load-velocity curve, an important factor when establishing load as a variable for targeting specific performance deficits during activities of daily living (ADL) (7) (Fig. 3).
Table: No title available.
Figure 3: The positions of four power tests along the load-velocity curve. Note that gait speed testing, which requires the least application of force against gravity, is toward the velocity end of the curve, whereas chair stand tests, which require the displacement of body weight in a nearly direct line against gravity, are located at the load end of the curve.
Endurance
Muscular endurance tests for older persons are sadly lacking. Timed tests such as push-up tests, held planks, curl-ups, and other traditional body weight-based assessments offer possibilities. In addition, researchers have used selected isoinertial lifts at submaximal loads (1) and multiple isokinetic contractions at moderate speeds (15) to assess endurance. Finally, traditional field tests, such as the 30-second chair stand and 30-second arm curl could potentially be adapted to provide valid assessments for muscular endurance in this population.
Applied Testing
Given that a major goal underlying the use of resistance training as an intervention with older individuals is the maintenance or restoration of independence, it also would be advantageous for the clinician to become familiarized with test batteries that assess the performance of ADL, such as the 10-item Continuous Scale Physical Functional Performance Battery (CS-PFP10), a continuous scale for assessing physical performance developed at the University of Georgia (6) or the Senior Fitness Test Battery assembled by Roberta Rikli and Jessie Jones (28). Each of these batteries can provide information concerning the neuromuscular factors to be targeted when developing prescriptive exercise interventions to address individuals’ assessed needs.
TRAINING STRENGTH
“Strength” can be defined as the maximal force a muscle can produce using a specific type of contraction (eccentric or concentric, isoinertial, isokinetic, or isometric). When considering training older individuals to enhance their strength, there are a number of factors to consider, such as the person’s training status, temporal location in the training cycle, and assessed needs. Concerning training status, it would be ill advised to begin any training program without allowing a period of gradual increase in load and volume. Resistance training delivers a significant overload to muscle, bone, and connective tissue; therefore, a gradual “tissue adaptation” period is appropriate before the targeted level of overload is applied. The length of this period is dependent on the individual. For example, our laboratories have used up to 8 weeks for nursing home patients who have not previously resistance trained; however, shorter tissue adaptation periods have proven feasible for more active, independently living persons. Fortunately, this period also can be used to make corrections in form because it uses relatively low loads. After the tissue adaptation phase, appropriate adjustments in intensity and volume should be made throughout any training cycle so that response can be maximized while the potential for acute or overuse injury is minimized. To this end, fitness and wellness professionals should familiarize themselves with the interactions among intensity, volume, and skill performance as they relate to periodization.
Having addressed these basic tenants of resistance training, the concept of providing a training prescription to address the older individuals’ assessed needs is the next logical topic. Biomechanically, the specific patterns of weakness should be considered. For example, poor performances on the chair stand (28) or stair-climbing (6) tests would be indicative of the need to emphasize the training of the lower body musculature, whereas poor performances on tests such as the arm curl (28) or gallon jug shelf (34) tests might dictate greater targeting of the upper body and core muscles. The biomechanical specificity inherent in providing truly targeted prescriptions also is obvious if fall reduction is a consideration. In addition to the typical interventions that might target the quadriceps, hamstrings, and triceps surae groups, less apparent choices, such as the dorsiflexors (40) and hip abductors and adductors (29), should be considered. Finally, in designing a training intervention to address ADL performance, it should be recognized that most daily tasks incorporate sequential movement patterns or “kinetic chains,” so imitative movements using bands, cable machines, or aquatic resistance are possible training tools once base strength is established.
Finally, the most common variables associated with training, loads (reps), sets, and frequency of training should be considered. These variables can be examined from two perspectives. The first is to consider the patterns frequently used in controlled training studies, and the second is to take into account the results of studies designed to specifically examine each variable. Both will be presented because the first provides insights into common usage patterns that have been shown to be successful in controlled training studies, whereas the second represents a more limited volume of work that may not have been incorporated into large training studies but may provide more exacting, albeit limited, information.
The most common loading pattern used during most strength training studies with older persons is between 70% and 80% of maximum (8 to 12 RM), and the ACSM guidelines reflect this pattern with recommended loads ranging from 65% to 75% of maximum (10 to 15 repetitions) (41). A meta-analysis by Rhea et al. (26) examining the variables mentioned above supports the use of moderate loading (≈60% 1 RM) for beginning lifters, graduating to high intensities (≈80% 1 RM) for more experienced lifters. And finally, in examining the impact of different loads along the training continuum, Campus et al. (5) recommended the use of between three and five repetitions (87.5% to 92.5% maximum) well above the 80% loads recommended by ACSM and used by most controlled studies. Given the success of the more conservative loading patterns and the lack of information concerning the effectiveness and safety of these higher loads with older persons, an abundance of caution argues for the use of 80% loading as the maximum for the older recreational lifter whose goal is improved independence and reduced falls probability; however, the published ACSM comment does concede that resistances as high as 85% are tolerated by older persons (41).
Concerning sets, the majority of the research performed has used between two and three sets per exercise. In addition, two recent meta-analyses have demonstrated the superiority of multiset over single-set programs in improving strength in both trained and untrained individuals (26,27). There is near universal agreement that the use of multiple sets is most effective after the individual has developed an increased level of performance. Therefore, the ACSM recommendation that olderpersons begin with a single set of each exercise and progress to no more than three sets seems appropriate; however, given the findings that support the use of four sets in younger untrained individuals and four or more for trained individuals (26), more research is required to determine the optimal set number. And finally, as was the case with loading, set number should vary in accordance with volume requirements during periodization.
Results addressing how many times per week training should occur are somewhat less controversial. The majority of the studies have used training frequencies of two to three times per week. The ACSM guidelines reflect this pattern, suggesting a training frequency of no fewer than two and no more than four times per week (41). When dose-response was specifically examined by Rhea et al. (26), a frequency of three times per week was found to be optimal for untrained individuals, whereas two times per week was more effective for trained exercisers. In most cases, the recommended recovery is 48 hours unless split training, incorporating different muscle groups on different training days, is used.
TRAINING HYPERTROPHY
Because of the recognized pattern of progressively declining muscle mass with increasing age, hypertrophy training has received considerable attention in the literature. As noted in the ACSM Position Stand on progressive models for resistance training (25), the loads used reflect the loading pattern suggested in the training continuum. Therefore, the majority of the training during hypertrophy-based programming is concentrated in the 6 to 12 repetition range with either higher (lower loads) or lower (higher loads) repetition programs producing lower levels of hypertrophy. Given the relationship between the volume of loading and hypertrophy, the consensus opinion is that multiple-set programs are superior to single-set programs and that 3 to 4 days per week would be optimal. An ancillary point made in the ACSM Position Stand is that having a portion of the training time dedicated to the strength end of the continuum may increase the levels of hypertrophy that can be achieved. One final caveat that should be addressed is the question of exercise tolerance with older, less conditioned individuals. Although there is no conclusive evidence on this issue, both the ACSM Position Stand on progressive resistance and the Current Comment on resistance training and the older adult suggest that 3 sets of 10 to 12 exercises performed 4 times per week constitute a safe and effective volume of work for the older person (25,41).
TRAINING POWER
In the early 1990s, a new training concept emerged as an intervention for aging, power training. Although it had been recognized for years that, with age, power declines nearly twice as quickly as strength (35), many researchers and practitioners were reluctant to use the high-speed techniques with older adults, even though they are an integral part of power training. Fortunately, this fear was all but dispelled by the research that took place during the next two decades. Because power is the rate of doing work, power training has habitually involved higher movement speeds, which presents some intrinsic problems. First of all, there is the interactive association between momentum and inertia when a mass is moved at a high velocity and must be decelerated to a stop at the end range of motion. Obviously, the stresses placed on the tissues have the potential to cause damage, especially if the momentum is increased because of gravity, as is the case with the eccentric portion of a lift. Therefore, it is common practice to limit the high-speed component to the concentric phase. High-speed training on plate-loaded machines with hard stops is understandably problematic. The use of free weights, although effective, is not recommended by ACSM for this population (41) and has the potential for connective tissue or muscle damage because of the inertial forces on the joints. Free-weight training also requires careful monitoring, has an extended learning curve, and demands continuous form correction especially during the early stages of training. For these reasons, most researchers have opted for pneumatic machines when providing high-speed overloads, and some of the newer cable machines, especially those that incorporate multiple pulleys, provide an excellent alternative. Another often overlooked, yet effective, modality forhigh-speed training is tubes and bands. And finally, although they may not be classically categorized as resistance training exercises, aquatic exercises, where increased speed and drag are conjoined, are a feasible alternative especially because they allow movement patterns imitative of daily activities.
The importance of power as it relates to independence (11) and fall probability (36) is well substantiated in the literature; however, the relationship between power training and functionality requires further exploration (24). As noted earlier in this section, power training is usually performed using low levels of resistance (≈50% 1 RM); however, there is good evidence that, from both a functional and biomechanical standpoint, the load used should vary considerably. For example, if gait speed is the goal, lower loads near 40% 1 RM are most effective, whereas chair rises and stair climbs, which require more direct movements against gravity, may be better addressed by loads between 70% and 80% 1 RM (Fig. 4) (7). Second, because of structural and physiological dissimilarities, different joints and their related muscle groups will require different optimal loads (31). For example, the long bones of the body, such as those comprising the knee and elbow joints respond well to high-speed training, whereas shorter lever systems, such as the ankle, show little response and may be better trained using heavier loading patterns (Fig. 5) (31). And third, power training is not limited to the weight room. I suggest that, during taper periods, which should occur after about 4 to 5 weeks of power training, multidirectional and multijoint “translational” drills can be used to increase movement velocity, which is the major factor in declining power with age (30). Concerning the number of sets and training frequency, the recommendations for power training mirror those for strength and hypertrophy training. When considering the duration of the training cycle, it seems that plateaus are reached within 4 weeks (32).
Figure 4: Illustration of training loads targeting different daily activities (light bar, balance and gait speed; dark bar, chair rise and stair climb). Note that both bars are displaced from the peak of the power curve.
Figure 5: A comparison of the longer third class lever at the knee characteristic of long bones and the shorter second class lever seen at the ankle. Muscles functioning above the knee joint will be more predisposed to velocity-based training, whereas those moving the ankle function more effectively at the load end of the load-velocity curve.
Figure 6: Field tests for power. Equations are provided for (A) the stair climb (14), (B) ramp (33), and (C) chair stand (37) power tests. See
Figures 6 to 8.
Field tests for power. Equations are provided for (A) the stair climb (14), (B) ramp (33), and (C) chair stand (37) power tests. See
Figures 6 to 8.
Field tests for power. Equations are provided for (A) the stair climb (14), (B) ramp (33), and (C) chair stand (37) power tests. See
Figures 6 to 8.
TRAINING ENDURANCE
“Muscular endurance,” defined as the ability of a muscle to maintain its power output, can be improved by strength training because a trained individual will use a lower percentage of his or her maximal strength when performing the same task compared with an untrained person. This relationship, however,is far from perfect. In fact, research has shown that the use of high-repetition (20 or more reps) systems with short recoveries (∼1 minute) can produce greater improvements inmuscle endurance than low-repetition programs (3 RM to 5 RM) using longer recoveries (∼3 minutes) or intermediate programs (9 RM to 12 RM) incorporating moderate recovery periods (2 minutes) (5). Current recommendations favor resistance levels ranging from 40% to 60% 1 RM (20 to 28 reps) using 2 to 3 sets, with a recovery of 1 to 2 minutes. Although there are limited controlled studies examining the relationship between muscular endurance and independence, there is a growing body of research affirming the importance of this relationship (38).
BODY COMPOSITION
Although the concept of body composition may appear to be out of place in the context of an article on resistance training and aging, it is an essential part of the discussion. In many ADL, such as rising from a chair, shopping, and climbing stairs, older persons need to move their body weight. This can become a major impediment to independence when sarcopenia is coupled with obesity (a condition called sarcopenic obesity). Although obesity or sarcopenia alone seems to have limited impact on daily activities, the combination is devastating to independence. As indicated in the section above, resistance training can have a positive impact on muscle cross-sectional area, thereby addressing the “sarcopenic” half of the equation; but what of the potential for using resistance training to affect changes in body composition? Although traditional wisdom has questioned the effectiveness of resistance training as a tool for affecting a positive change in body composition, circuit training programs have been shown to elicit greater metabolic cost than treadmill training when the two are matched for duration and energy expenditure (2). In addition, both traditional hypertrophy and circuit training programs can produce significantly higher levels of excess postexercise oxygen consumption (EPOC) than steady state training programs (8). More recently, it has been demonstrated that, using similar volumes of work, explosive training at 60% 1 RM can produce greater energy expenditures than either slow training at 60% 1 RM or explosive training at 80% 1 RM (20). From the point of view of independence, this provides a “two-for-one” special because the explosive nature of the training can improve power while it increases energy expenditure.
CONCLUSIONS
As would be expected given the concept of training specificity, resistance training methodologies can be tailored to match the needs of the older individual. Targeted training not only offers the potential for more effective training, it also should reduce training time because it more efficiently addresses the participant’s needs. And finally, prescriptive programs based on assessed needs fit nicely into the Exercise is Medicine® initiative established by ACSM.
Due to space constraints, the complete list of references will appear online at [https://links.lww.com/FIT/A11].
CONDENSED VERSION AND BOTTOM LINE
Resistance training is now an integral part of most programs designed to improve independence and reduce falls in older persons. This modality, however, is not a one-dimensional training tool. Using validated assessment tools and variations in training methods and equipment, fitness and health professionals can maximize the positive impact that resistance training can have on each individual. This information is critical not only to the person but to the society, given the burden of an increasing aging demographic and the need for prevention to reduce the costs associated with our current medical model.
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