Adults older than 65 years make up an increasingly larger proportion of the US population. The Centers for Disease Control and Prevention (CDC) projects that with longer life spans and aging of the baby boomers, the population of older adults will double over the next 25 years to about 72 million and will account for about 20% of the US population.1 An observed consequence of aging is a decline in muscle performance that includes a loss of both muscle strength and muscle power.2 This decline in muscle performance with aging can lead to loss of function and independence2 and is a predictor of disability in older adults.3 Loss of functional independence and disability requires assistance to be provided either at home by family and friends, through home health or community-based services, or institutional settings such as assisted living or nursing care facilities.
Muscle-strengthening activities such as resistance exercise are safe for older adults and have been shown to improve muscle performance.4 Resistance exercise has also been shown to improve important functional aspects of physical performance such as gait speed and sit-to-stand time.5 The US Department of Health and Human Services recognized the importance of resistance exercise for all ages and included resistance exercise recommendations in its 2008 Physical Activity (PA) Guidelines for Americans.6 The recommendation for older adults is no different from adults in general and advises that older adults should perform moderate-to-high intensity muscle-strengthening exercise using all major muscle groups on 2 or more days per week in addition to aerobic activity.6
The muscle-strengthening guidelines, however, are not as well defined as the guidelines for aerobic activity. For example, there is ample evidence to support that 150 minutes per week of moderate to vigorous physical activity (MVPA) is sufficient for health benefits and that additional health benefits are acquired with 300 minutes or more per week.6 There is limited evidence to support whether resistance exercise performed a minimum of 2 times per week is associated with measures of physical performance that are critical indicators of functional independence in older adults. There is also no evidence that looks at whether performing resistance exercise for all major muscle groups (eg, limbs and trunk) is needed for benefits in physical performance. The purposes of this study were to assess muscle-strengthening and aerobic PA behaviors in older adults and to determine the relationship between the PA behaviors and physical performance measures. If adherence to muscle-strengthening guidelines is associated with improved physical performance measures, then advocating for PA as a health behavior that includes an aerobic and muscle-strengthening component could potentially play a role in moderating development and progression of frailty in older adults.
A cross-sectional study design was used in the present investigation. The participants were classified according to their status on the 2008 PA Guidelines, which served as the independent variables of the study. The dependent variables of the study were physical performance measures related to physical function in older adults.
Community-dwelling, ambulatory men and women 60 years or older were recruited from the general community during the period of January 2014 to October 2015, using a flyer and word of mouth. Exclusion criteria included the following: (a) use of an assistive device for walking other than a cane, (b) dizziness or vertigo in the last 4 weeks, (c) pain with weight bearing, (d) diagnosed balance disorders, (e) diagnosis of rheumatoid arthritis, or (f) history of a cardiac event within the last year that would limit their ability to perform the physical performance tests. Participants were allowed to use a cane during testing but had to have the ability to walk independently. This recruitment process resulted in 85 individuals who qualified for the study and wished to participate. Each of these individuals read and signed an informed consent approved by the Institutional Review Board at Texas Woman's University.
Physical activity behavior
Participants self-reported muscle-strengthening and aerobic PA using the Tracking Resistance Exercise and Strength Training (TREST) survey. The TREST is an internet-based survey, developed at The Cooper Institute and the University of North Texas (http://trest.cooper.unt.edu/trest/). The survey uses visual modeling of specific muscle-strengthening activities that participants can view to provide a complete understanding of their own PA behaviors with specific interest in muscle-strengthening activities. The survey of muscle-strengthening activities begins by asking, “In a typical week, do you do activities to increase muscle strength or tone, such as lifting weights, using weight machines, using exercise bands, or doing calisthenics (eg, push-ups, sit-ups, and pull-ups)?” If the participants answered “yes” to that question, they were presented with categories of exercises such as squat/leg press with looping videos demonstrating 3 or 4 different ways of performing exercises using this group of muscles. They were asked, “Do you perform this type of exercise or something similar to it?” If they answered “yes,” a follow-up question was presented asking how many times per week they typically perform that exercise. Responses to all TREST questions were automatically entered into an Excel file to be later retrieved by the investigator at a password-protected data retrieval site. Similar questions were asked to determine number of minutes of moderate and vigorous aerobic PA to calculate MVPA minutes per week of aerobic activity. The TREST has been shown to have test-retest reliability: in a reliability study of the TREST, Knell et al7 demonstrated that when the survey was administered approximately 2 weeks apart, responses to each of the muscle-strengthening items demonstrated agreement ranging from 75% to 94% while total minutes of MVPA reported had a reliability coefficient of α= 0.71. The TREST was used in this study to record basic demographic information and PA behavior (aerobic and muscle strengthening) in a typical week.
Physical performance measures
Physical performance measures were taken upon completion of the internet-based survey of PA behavior. Because the measures did not require any specialized equipment or testing environment, they were either taken at the university, at a community center, church, or other place of convenience. A description of the 4 physical performance measures follows.
An overall assessment of muscle strength was obtained by measuring grip strength with a Jamar (Sammons Preston Inc, Bolingbrook, Illinois) grip dynamometer. Standardized testing procedures developed by the American Society for Hand Therapists8 , 9 were used to measure strength of the dominant hand. Two trials were performed and the average of the trials was recorded to the nearest kilogram. Intra- and interrater reliability of the Jamar dynamometer for measuring grip strength in healthy individuals has been previously demonstrated (intraclass correlation coefficient [ICC] = 0.87-0.97).10 Grip strength was selected as an overall assessment of muscle strength because it has been shown to be good surrogate measure of overall muscle strength and lower values of grip strength have been associated with all-cause mortality11 , 12 and disability in older adults.11
Lower extremity functional muscle strength was assessed using the five-time sit-to-stand test (FTSST). The FTSST assesses the amount of time in seconds that an individual takes to come to standing from a chair and sit back down 5 times. With arms crossed in front of their chest, participants were asked to stand from a standard height chair (45 cm) and sit back down 5 times as rapidly as they could. A single-timed trial was completed and recorded for data analysis. The FTSST has been shown to have good test-retest reliability (ICC = 0.81).13 Importantly, longer time to complete the FTSST has been shown to be predictive of developing instrumental activities of daily living-related disability at 3-year follow-up.14
Lower extremity functional power was assessed using the stair climb test (SCT). Lower extremity muscle power has been shown to have a stronger relationship to functional limitations and disability than muscle strength2 and is related to walking performance and frailty in older adults.15 For the SCT, time to ascend 8 stairs as quickly as possible was recorded to the nearest 0.01 second. Time was started when the participants took their first step and ended when both feet reached the eighth step. Participants were allowed to use handrails for safety but were instructed not to use the handrails to pull themselves up. Two trials were recorded with at least 1-minute rest in between the trials and the faster of the 2 timed trials was used for data analysis. Test-retest reliability of the timed stair test has been shown to be excellent with an ICC of 0.99.16 Time on the SCT was then used in the calculation of power using the formula: Power (W) = body mass (kg) × total vertical distance achieved on stair climb (m) × acceleration of gravity (m/s2)/time on SCT (seconds).16
Gait speed was assessed using the timed 10-m walk test (10-MWT). Gait speed is an important variable in older adults that has been shown to be a strong predictor of impending frailty, needing living assistance, and death.17 , 18 Measurement of gait speed using the 10-MWT in healthy older adults has been shown to have excellent test-retest reliability (ICC = 0.96-0.98).19
For measurement of the 10-MWT, a dynamic start and stop was used to reduce the effects of acceleration and deceleration. Participants were asked to walk along a measured 20-m walkway as fast as they could safely, but only the time to walk the middle 10 m was recorded. The first and last 5 m distances were used for acceleration and deceleration, respectively.
We measured 3 trials of the 10-MWT with 1-minute rest in between trials. The average of the trials was recorded in seconds for data analysis.
Participants started the data collection session by completing the TREST on-line survey using a laptop computer provided by the investigator. After providing log on information, members of the research team allowed participants to complete the survey privately but were in close enough proximity that they could answer questions if needed. After completion of the survey, physical performance tests were conducted. Uniform instructions and test procedures were used for all tests. Grip strength, FTSST, SCT, and 10-MWT were performed in the same order, as described earlier. Rest for 3 to 5 minutes was provided between each of the physical performance tests.
All data analyses were performed using IBM SPSS Statistics for Windows, version 19 (IBM Corp, Armonk, New York). Descriptive statistics were calculated for subject characteristics and the 4 physical performance measures, reporting means, and standard deviations. To assess the relationship between the PA behaviors and physical performance measures, participants were grouped by whether they met 2008 PA Guidelines for (1) muscle strengthening 2 or more days per week, (2) muscle strengthening 2 or more days per week using all major muscle groups (upper extremity, lower extremity and trunk), and (3) 150 minutes or more per week of aerobic MVPA.6 We conducted a final analysis looking at physical performance measures for participants who met neither the aerobic or muscle-strengthening guideline compared with participants who met both. Multivariate analyses were then used to assess significance of differences between the grouping variables on the 4 physical performance measures. Significant results were followed with one-tailed t tests because there is no reason to believe that meeting the PA guidelines would result in worse scores on physical performance measures. Effect sizes were calculated and an α level of 0.05 was used to determine significance.
Eighty-five community-dwelling, ambulatory adults (50 women, 35 men) with a mean (standard deviation [SD]) age of 67.5 (5.6) years completed the TREST survey and had physical performance measures taken. The sample consisted primarily of Caucasian men and women (almost 95%) who were highly educated, with 50% holding a 4-year college degree. Mean (SD) body mass index for the sample was 26.7 (4.5) kg/m2. Although participants who used a cane for ambulation were eligible for the study, none of the older adults who took part in the study actually used a cane during testing or reported using one at home.
When participants were grouped based on whether they met or did not meet the 2008 muscle-strengthening guidelines of performing resistance exercise 2 times or more per week, 37 (43.5%) individuals were found to have met the guideline and 48 (56.5%) did not meet. Table 1 shows mean values (SD) for measures of physical performance by group (meeting vs not meeting guidelines). The multivariate test (Hoteling's T) used to compare the 4 physical performance measures between the groups was significant (P = .001). Follow-up t tests revealed that older adults who reported doing resistance exercise at least twice per week had significantly better grip strength (P = .033) and scores on the SCT (P = .007). Those who met the guidelines also scored better on the 10-MWT and FTSST than those who did not meet guidelines, but the difference was not statistically significant (Table 1).
When grouped by a more stringent interpretation of the 2008 muscle-strengthening guidelines of performing resistance exercise 2 times or more per week using all major muscle groups (UE, LE, and trunk), only 23 (27%) participants met the guidelines. Table 2 shows mean values (SD) for measures of physical performance for those who met the more stringent guidelines versus those who did not meet them. The multivariate test (Hotelling's T) used to compare the 4 physical performance measures between the groups was again significant (P = .004). Follow-up t tests once again revealed that older adults who met the more stringent muscle-strengthening guidelines performed better than those who did not meet guidelines on all 4 physical performance measures, but differences were only statistically significant for the SCT (P = .03) and FTSST (P = .02) (Table 2).
When participants were grouped based on whether they met or did not meet the 2008 guidelines for aerobic activity (≥150 minutes of MVPA), 51 (60%) participants were found to have met the guidelines whereas 34 (40%) did not meet them. Table 3 shows mean values (SD) for measures of physical performance for those who met the aerobic activity guidelines versus those who did not meet them. The multivariate test (Hoteling's T) used to compare the 4 physical performance measures between the groups was again significant (P < .001). Follow-up t tests revealed that older adults who reported doing 150 minutes or more per week of MVPA had performed significantly better on the SCT (P = .007), the FTSST (P = .018), and the 10-MWT (P = .024) than those who did not meet guidelines. Although average grip strength was better in the group meeting aerobic activity guidelines compared to the group that did not meet, the difference did not reach statistical significance (P = .145) (Table 3).
Finally, we grouped participants by those who met both guidelines for performing 150 minutes or more of MVPA and resistance exercise 2 times or more per week (n = 26) compared with those who met neither of the guidelines (n = 24). The remaining 34 participants met one of the guidelines (either the strengthening guideline or the aerobic exercise guideline), so they were not included in this analysis. The multivariate test comparing the 4 physical performance measures between these 2 groups was significant (P = .001). Follow-up t tests were significant for all 4 physical performance measures (P < .05), indicating that older adults who met both aerobic and muscle-strengthening guidelines performed better than those who met neither guideline (Table 4).
In the assessment of muscle-strengthening and PA behaviors in our sample of older adults, 43.5% reported performing muscle-strengthening activity 2 time or more per week and 60% reported meeting guidelines for performing 150 minutes or more per week of MVPA. When comparing our reported PA behaviors with those reported by the CDC from their survey of the nation's health in Health, United States, 2015, a larger portion of our participants met the guidelines than the nation overall. In Health, United States, the CDC reports that in 2014, 42.4% of older adults met the 2008 PA Guidelines for aerobic activity compared with our 60%, and 19% met the muscle-strengthening guidelines of 2 times or more per week for all major muscle groups compared with our 27%.20 Although our participants were more active overall than older adults who participated in the CDC's survey of the nation's health, interpretation of our participants' PA behavior, and especially their muscle-strengthening behavior, is that their level of PA participation is low for older adults 60 years or older.
To determine the relationship between the PA behaviors and physical performance measures, we assessed the differences for 3 different groupings: (a) whether they met or did not meet the muscle-strengthening guideline of performing resistance exercise 2 times or more per week, (b) whether they met or did not meet the muscle-strengthening guideline of performing resistance exercise 2 times or more per week using all major muscle groups, and (c) whether they met or did not meet the guideline for aerobic activity (≥150 min/wk of MVPA). Regardless of which guideline was used, participants who met the PA guideline performed better on each of the 4 physical performance measures than participants who did not meet the guideline. However, when looking at which of the differences in physical performance were statistically significant, meeting or not meeting each of the 3 different guidelines yielded different results. We were most interested in learning about the relationship between muscle-strengthening habits and physical performance measures. In particular, we were interested in determining whether performing resistance exercise 2 times per week or more is enough to yield benefits in physical performance. Or, does an individual need to perform resistance exercise for all major muscle groups at least 2 times per week as subscribed by the 2008 PA Guidelines? Our results showed that participants who met the guideline for resistance exercise at least 2 times per week performed significantly better on grip strength and the SCT than participants who did not meet this guideline. However, participants who performed resistance exercise for all major muscle groups (core, upper, and lower extremities) at least 2 times per week performed significantly better on the FTSST and the SCT. When comparing participants who met or did not meet the guideline for 150 minutes per week of MVPA, we found that those who met the guideline for aerobic activity performed significantly better on all physical performance measures with exception of grip strength.
Our final comparison of participants who met both guidelines (for aerobic and muscle strengthening) to those who met neither yielded some important findings. Participants who met both guidelines performed significantly better on all physical performance measures compared with those who met neither, and effect sizes of differences between these 2 groups were moderate to large (Table 4). That is, participants who met both guidelines were stronger, had better lower extremity power, and faster gait velocities compared with participants who met neither.
Better performance on gait velocity and grip strength is important because these are 2 of the most common factors used to determine frailty in older adults17 , 18 , 21 and are considered by many to represent the most suitable measures in research and clinical assessment of older adults.22 Although there is no consensus for a gold standard appraisal of frailty, there is agreement that frailty is a “state of high vulnerability for adverse health outcomes.”23 Research has demonstrated that frailty is significantly predictive of disability, falls, and hospitalization in older adults17 , 24 as well as high risk for reduced mobility and increased dependence for performing activities of daily living.17 , 25 Importantly, frailty is reversible.26 , 27 Therefore, the results of our study have implications for the type of PA that may be most appropriate for preventing, slowing, or delaying frailty. Of the groupings that we studied, only participants who met both aerobic and muscle-strengthening guidelines performed significantly better on all 4 physical performance measures when compared with participants who met neither guidelines.
Our findings are in agreement with other results and recommendations related to the health benefits of aerobic PA and resistance exercise in older adults.4 , 28 Specifically, the American Heart Association supports resistance exercise for older persons with coronary heart disease and heart failure.28 Older individuals with cardiovascular disease adapt to resistance exercise with a variety of physical performance improvements without adverse health consequences related to their disease status.28 Thus, for apparently healthy older adults and older adults with cardiovascular disease, resistance exercise provides improvements in physical functioning with little increase in the risk of negative health events.
Limitations of our study include a small and relatively homogenous sample. Although a sample of 85 older adults seems adequate, the numbers reduce substantially once they are grouped by meeting or not meeting PA guidelines. We would have liked to further explore grouping our participants by those who met one guideline but not the other (eg, those who met strengthening guideline but not the aerobic guideline). However, doing so produced groupings that were too small to analyze statistically. It is also possible that men and women have differing relationships between PA behavior and physical performance measures, but our sample was not large enough to look at men and women independently. We suggest that our study be replicated using a larger, more diverse sample of older adults in order to further validate our findings and to increase generalizability to a wider segment of the older adult population. In addition, a randomized controlled trial that uses aerobic and muscle-strengthening guidelines as an intervention to affect frailty should be conducted.
This study begins to explore the muscle-strengthening habits of older men and women and the relationship between meeting the 2008 PA Guidelines and physical performance measures that have a known association with frailty, disability, and dependence in performing activities of daily living. The results of our study revealed that although older adults who met guidelines for performing muscle strengthening 2 times per week or more, muscle strengthening 2 times per week or more for all major muscle groups, or 150 minutes per week or more of MVPA performed better on some of the physical performance measures, but not all of them. Based on the results of our study, we conclude that meeting guidelines for both aerobic and muscle-strengthening activities may be the most effective way of preserving muscle strength, muscle power, and gait velocity in older adults but this conclusion must be tested with an intervention study.
1. Centers for Disease Control and Prevention. The State of Aging and Health in America 2013. Atlanta, GA: Centers for Disease Control and Prevention, U.S. Department of Health and Human Services; 2013.
2. Puthoff ML, Nielsen DH. Relationships among impairments in lower-extremity strength and power, functional limitations, and disability in older adults. Phys Ther. 2007;87(10):1334–1347.
3. Goodpaster BH, Park SW, Harris TB, et al The loss of skeletal muscle strength, mass, and quality in older adults: the health, aging and body composition study. J Gerontol A Biol Sci Med Sci. 2006;61(10):1059–1064.
4. Fiatarone MA, Marks EC, Ryan ND, Meredith CN, Lipsitz LA, Evans WJ. High-intensity strength training in nonagenarians: effects on skeletal muscle. JAMA. 1990;263(22):3029–3034.
5. Liu CJ, Latham NK. Progressive resistance strength training for improving physical function in older adults. Cochrane Database Syst Rev. 2009;(3):CD002759.
6. U.S. Department of Health and Human Services. 2008 Physical Activity Guidelines for Americans. Washington, DC: U.S. Department of Health and Human Services; 2008.
7. Knell G, Morrow JR, Vingren J, Jackson AW. Reliability of an online system to assess muscle strengthening
activities in kinesiology students. Med Sci Sports Exerc. 2014;46(5S).
8. Fess EE. The need for reliability and validity in hand assessment instruments. J Hand Surg Am. 1986;11(5):621–623.
9. Hamilton A, Balnave R, Adams R. Grip strength testing reliability. J Hand Ther. 1994;7(3):163–170.
10. Peolsson A, Hedlund R, Oberg B. Intra- and inter-tester reliability and reference values for hand strength. J Rehabil Med. 2001;33(1):36–41.
11. Bohannon RW. Hand-grip dynamometry predicts future outcomes in aging adults. J Geriatr Phys Ther. 2008;31(1):3–10.
12. Ling CH, Taekema D, de Craen AJ, Gussekloo J, Westendorp RG, Maier AB. Handgrip strength and mortality in the oldest old population: the Leiden 85-plus study. CMAJ. 2010;182(5):429–435.
13. Bohannon RW. Test-retest reliability of the five-repetition sit-to-stand test: a systematic review of the literature involving adults. J Strength Cond Res. 2011;25(11):3205–3207.
14. Zhang F. Performance on five times sit-to-stand task as a predictor of subsequent falls and disability in older persons. J Aging Health. 2013;25(3):478–492.
15. Zech A, Steib S, Sportwiss D, Freiberger E, Pfeifer K. Functional muscle power testing in young, middle-aged, and community-dwelling nonfrail and prefrail older adults. Arch Phys Med Rehabil. 2011;92(6):967–971.
16. Bean JF, Kiely DK, LaRose S, Alian J, Frontera WR. Is stair climb power a clinically relevant measure of leg power impairments in at-risk older adults? Arch Phys Med Rehabil. 2007;88(5):604–609.
17. Fried LP, Tangen CM, Walston J, et al Frailty
in older adults: evidence for a phenotype. J Gerontol A Biol Sci Med Sci. 2001;56(3):M146–M156.
18. Lang P, Michel J, Zekry D. Frailty
syndrome: a transitional state in a dynamic process. Gerontology. 2009;55(5):539–549.
19. Peters DM, Fritz SL, Krotish DE. Assessing the reliability and validity of a shorter walk test compared with the 10-meter walk test for measurements of gait speed in healthy, older adults. J Geriatr Phys Ther. 2013;36(1):24–30.
20. Centers for Disease Control and Prevention. National Center for Health Statistics, Health, United States, 2009. Washington, DC: Centers for Disease Control and Prevention, U.S. Department of Health and Human Services; 2010.
21. Sutton JL, Gould RL, Daley S, et al Psychometric properties of multicomponent tools designed to assess frailty
in older adults: a systematic review. BMC Geriatr. 2016;16(1):55.
22. Jones DM, Song X, Rockwood K. Operationalizing a frailty
index from a standardized comprehensive geriatric assessment. J Am Geriatr Soc. 2004;52(11):1929–1933.
23. Al Snih S, Graham JE, Ray LA, Samper-Ternent R, Markides KS, Ottenbacher KJ. Frailty
and incidence of activities of daily living disability among older Mexican Americans. J Rehabil Med. 2009;41(11):892–897.
24. Boyd CM, Xue Q, Simpson CF, Guralnik JM, Fried LP. Frailty
, hospitalization, and progression of disability in a cohort of disabled older women. Am J Med. 2005;118(11):1225–1231.
25. Woods NF, LaCroix AZ, Gray SL, et al Frailty
: emergence and consequences in women aged 65 and older in the women's health initiative observational study. J Am Geriatr Soc. 2005;53(8):1321–1330.
26. Binder EF, Schechtman KB, Ehsani AA, et al Effects of exercise training on frailty
in community-dwelling older adults: results of a randomized, controlled trial. J Am Geriatr Soc. 2002;50(12):1921–1928.
27. Gill TM, Baker DI, Gottschalk M, Peduzzi PN, Allore H, Byers A. A program to prevent functional decline in physically frail, elderly persons who live at home. N Engl J Med. 2002;347(14):1068–1074.
28. Williams MA, Haskell WL, Ades PA, et al Resistance exercise in individuals with and without cardiovascular disease: 2007 update: A scientific statement from the American Heart Association Council on Clinical Cardiology and Council on Nutrition, Physical Activity, and Metabolism. Circulation. 2007;116(5):572–584.