Assessment of analytical methods used to measure changes in body composition in the elderly and recommendations for their use in phase II clinical trials

It is estimated that in the next 20 years, the amount of people greater than 65 years of age will rise from 40 to 70 million, and will account for 19% of the total population. Age-related decreases in muscle mass and function, known as sarcopenia, have been shown to be related to functional limitation, frailty and an increased risk of morbidity and mortality. Therefore, with an increasing elderly population, interventions that can improve muscle mass content and/or function are essential. However, analytical techniques used for measurement of muscle mass in young subjects may not be valid for use in the elderly. Therefore, the purpose of this review is to examine the applied specificity and accuracy of methods that are commonly used for measurement of muscle mass in aged subjects, and, to propose specific recommendations for the use of body composition measures in phase II clinical trials of function-promoting anabolic therapies.

Sarcopenia: an undiagnosed condition in older adults. Current consensus definition: prevalence, etiology, and consequences. International working group on sarcopenia

Sarcopenia, the age-associated loss of skeletal muscle mass and function, has considerable societal consequences for the development of frailty, disability, and health care planning. A group of geriatricians and scientists from academia and industry met in Rome, Italy, on November 18, 2009, to arrive at a consensus definition of sarcopenia. The current consensus definition was approved unanimously by the meeting participants and is as follows: Sarcopenia is defined as the age-associated loss of skeletal muscle mass and function. The causes of sarcopenia are multifactorial and can include disuse, altered endocrine function, chronic diseases, inflammation, insulin resistance, and nutritional deficiencies. Although cachexia may be a component of sarcopenia, the 2 conditions are not the same. The diagnosis of sarcopenia should be considered in all older patients who present with observed declines in physical function, strength, or overall health. Sarcopenia should specifically be considered in patients who are bedridden, cannot independently rise from a chair, or who have a measured gait speed less that 1 m/s(-1). Patients who meet these criteria should further undergo body composition assessment using dual energy x-ray absorptiometry with sarcopenia being defined using currently validated definitions. A diagnosis of sarcopenia is consistent with a gait speed of less than 1 m·s(-1) and an objectively measured low muscle mass (eg, appendicular mass relative to ht(2) that is ≤ 7.23 kg/m(2) in men and ≤ 5.67 kg/m(2) in women). Sarcopenia is a highly prevalent condition in older persons that leads to disability, hospitalization, and death.

Neuromuscular contributions to age-related weakness

BACKGROUND

Declines in skeletal muscle mass and quality are important factors contributing to age-related weakness. Neural activation of agonist and antagonist muscles may also be important contributing factors.

METHODS

We conducted a review of the scientific literature on older adults to determine (a) methodologies used to quantify activation, (b) the potential role of agonist and antagonist activation on weakness, and (c) some possible neurophysiological mechanisms that may underlie impaired activation.

RESULTS

The cumulative evidence indicates that agonist activation is impaired in some, but not all, older adults and that this impairment contributes to age-related weakness. It is possible that antagonist coactivation also plays a role in age-related weakness, though a definitive link has not been established.

CONCLUSION

Future research should focus on improving quantitative measurement and mechanistic understanding of impaired activation with aging.

Muscle performance and physical function are associated with voluntary rate of neuromuscular activation in older adults

BACKGROUND

Muscle power is related to mobility function in older adults, and effective power production requires rapid neuromuscular activation. Accordingly, this study examines the association of neuromuscular activation rate with muscle performance in persons of different age and mobility function.

METHODS

Participants were recruited to three experimental groups: middle-aged healthy adults (MH), older healthy adults (OH), and older adults with mobility limitations (OML). OH and OML were primarily differentiated by performance on the Short Physical Performance Battery (SPPB). Muscle performance (acceleration and power) and electromyography (EMG) were recorded during a maximal-effort leg press task at an absolute resistance (260 N) and at a relative resistance (70% of the one-repetition maximum [1 RM]). Neuromuscular activation rate was quantified as pre-movement time (duration between EMG onset and movement onset) and the rate of EMG rise.

RESULTS

Pre-movement time, rate of EMG rise, leg press acceleration, and leg press power were lower in OML relative to MH and OH but did not differ between OH and MH, with the exception of power at 70% 1RM. Across all older participants, rate of EMG rise was positively associated with acceleration, power, and the SPPB score.

CONCLUSIONS

Slowing of neuromuscular activation rate is associated with compromised dynamic muscle performance, which may contribute to mobility limitations in some older adults. Future research should identify the precise neurophysiological impairments that contribute to declines in neuromuscular activation rate and mobility function with aging.

Habitual physical activity levels are associated with performance in measures of physical function and mobility in older men

OBJECTIVES

To determine whether objectively measured physical activity levels are associated with physical function and mobility in older men.

DESIGN

Cross-sectional.

SETTING

Academic research center.

PARTICIPANTS

Eighty-two community-dwelling men aged 65 and older with self-reported mobility limitations were divided into a low-activity and a high-activity group based on the median average daily physical activity counts of the whole sample.

MEASUREMENTS

Physical activity according to triaxial accelerometers; physical function and mobility according to the Short Physical Performance Battery (SPPB), gait speed, stair climb time, and a lift-and-lower task; aerobic capacity according to maximum oxygen consumption (VO(2) max); and leg press and chest press maximal strength and peak power.

RESULTS

Older men with higher physical activity levels had a 1.4-point higher mean SPPB score and a 0.35-m/s faster walking speed than those with lower physical activity levels. They also climbed a standard flight of stairs 1.85 seconds faster and completed 60% more shelves in a lift-and-lower task (all P<.01); muscle strength and power measures were not significantly different between the low- and high-activity groups. Correlation analyses and multiple linear regression models showed that physical activity is positively associated with all physical function and mobility measures, leg press strength, and VO(2) max.

CONCLUSION

Older men with higher physical activity levels demonstrate better physical function and mobility than their less-active peers. Moreover, physical activity levels are predictive of performance in measures of physical function and mobility in older men. Future work is needed to determine whether modifications in physical activity levels can improve or preserve physical performance in later life.

Relationship between physical functioning and physical activity in the lifestyle interventions and independence for elders pilot

OBJECTIVES

To determine whether participation in usual moderate-intensity or more-vigorous physical activity (MVPA) is associated with physical function performance and to identify sociodemographic, psychosocial, and disease-related covariates that may also compromise physical function performance.

DESIGN

Cross-sectional analysis of baseline variables of a randomized controlled intervention trial.

SETTING

Four academic research centers.

PARTICIPANTS

Four hundred twenty-four older adults aged 70 to 89 at risk for mobility disability (scoring <10 on the Short Physical Performance Battery (SPPB)) and able to complete the 400-m walk test within 15 minutes.

MEASUREMENTS

Minutes of MVPA (dichotomized according to above or below 150 min/wk of MVPA) assessed according to the Community Healthy Activities Model Program for Seniors questionnaire, SPPB score, 400-m walk test, sex, body mass index (BMI), depressive symptoms, age, and number of medications.

RESULTS

The SPPB summary score was associated with minutes of MVPA (ρ=0.16, P=.001). In multiple regression analyses, age, minutes of MVPA, number of medications, and depressive symptoms were associated with performance on the composite SPPB (P<.05). There was an association between 400-m walk time and minutes of MVPA (ρ=-0.18; P<.001). In multiple regression analyses, age, sex, minutes of MVPA, BMI, and number of medications were associated with performance on the 400-m walk test (P<.05).

CONCLUSION

Minutes of MVPA, sex, BMI, depressive symptoms, age, and number of medications are associated with physical function performance and should all be taken into consideration in the prevention of mobility disability.

Multi-step immunofluorescent analysis of vitamin D receptor loci and myosin heavy chain isoforms in human skeletal muscle

Vitamin D receptors have been shown to be present in human skeletal muscle using different techniques. We developed a multi-staining immunofluorescent method to detect vitamin D receptor expression and co-localize it with myosin heavy chain isoform expression in skeletal muscle biopsies in older female subjects. Serial sections were cut from frozen samples obtained by needle biopsy of the vastus lateralis. Samples were probed with a primary vitamin D receptor monoclonal antibody and then re-probed with a type IIa myosin heavy chain isoform-specific antibody. Independent unfixed sections followed a similar protocol and were probed with type IIx and type I myosin heavy chain isoform-specific antibodies. Immunohistochemistry and fluorescent microscopy co-localized vitamin D receptor loci and myosin heavy chain isoforms in whole skeletal muscle sections. We quantified intranuclear vitamin D receptor staining patterns and number of individual muscle fiber subtypes within a muscle section. Immunohistochemical staining of the vitamin D receptor was confirmed by Western blot using the same monoclonal antibody. This multi-staining immunofluorescent technique allows for measurement of intranuclear vitamin D receptor expression in the context of the specific muscle fiber type profile in a single section. This method can thus be a useful approach to study potential relationships between muscle fiber subtypes and vitamin D receptor expression.

Impaired voluntary neuromuscular activation limits muscle power in mobility-limited older adults

BACKGROUND

Age-related alterations of neuromuscular activation may contribute to deficits in muscle power and mobility function. This study assesses whether impaired activation of the agonist quadriceps and antagonist hamstrings, including amplitude- and velocity-dependent characteristics of activation, may explain differences in leg extension torque and power between healthy middle-aged, healthy older, and mobility-limited older adults.

METHODS

Torque, power, and electromyography were recorded during maximal voluntary leg extension trials across a range of velocities on an isokinetic dynamometer.

RESULTS

Neuromuscular activation was similar between middle-aged and older healthy groups, with differences in torque and power explained predominantly by muscle size. However, the older mobility-limited group demonstrated marked impairment of torque, power, and agonist muscle activation, with the greatest deficits occurring at the fastest movement velocities. Agonist muscle activation was found to be strongly associated with torque output.

CONCLUSIONS

Similar neuromuscular activation between the middle-aged and older healthy groups indicates that impaired voluntary activation is not an obligatory consequence of aging. However, the finding that the mobility-limited group exhibited impaired activation of the agonist quadriceps and concomitant deficits in torque and power output suggests that neuromuscular activation deficits may contribute to compromised mobility function in older adults.

Lower extremity strength and power asymmetry assessment in healthy and mobility-limited populations: reliability and association with physical functioning

BACKGROUND AND AIMS

This study assessed the reliability of evaluating asymmetrical strength and power deficits in the lower limbs of healthy middle-aged, healthy older and mobility-limited elders. We also explored the relationship between limb asymmetry and physical functioning.

METHODS

We evaluated baseline knee extension strength and power asymmetry data from a cohort of older adults (n=57; 74.2±0.9 yrs, 26 male) who participated in a lower body strength training study (TS) and from a cross-sectional study of community dwelling volunteers. Cross-sectional participants were recruited into: healthy middle-aged (MH) (n=31; 47.4±4.8 yrs, 14 male), healthy older (OH) (n=28; 74.0±3.6 yrs, 16 male) and mobility-limited older (OML) (n=34; 77.8±4.5 yrs, 16 male) groups. Knee extensor strength (1RM) and power asymmetry at 40% and 70% of 1RM were evaluated for test-retest reliability using intraclass correlation coefficients (ICCs).

RESULTS

Knee extension 1RM, and peak power at 40% and 70% asymmetry ICCs exhibited excellent to good reliability in the TS and OML groups (TS= 0.8, 0.7 and 0.7, respectively; OML= 0.7, 0.7, and 0.9, respectively) but not in the MH and OH groups. No consistent association between lower limb asymmetry and measures of physical functioning was observed.

CONCLUSIONS

Assessment of lower limb strength and power asymmetry is more reliable in mobility-limited elders when compared to healthy middle-aged and older subjects. The relationship of lower limb asymmetry to physical functioning is poor, in contrast to associations between the absolute strength and power of the individual limbs and physical functioning.

Effects of chronic overload on muscle hypertrophy and mTOR signaling in young adult and aged rats

We examined the effect of 28 days of overload on mammalian target of rapamycin (mTOR) and extracellular signal-regulated kinase (ERK) signaling in young adult (Y; 6-month old) and aged (O; 30-month old) Fischer 344 x Brown Norway rats subjected to bilateral synergist ablation (SA) of two thirds of the gastrocnemius muscle or sham surgery (CON). Although plantaris (PLA) muscle hypertrophy was attenuated by aging, mTOR phosphorylation was 44% and 35% greater in Y SA and O SA compared with CON (p = .038). Ribosomal protein S6 phosphorylation was 114% and 24% higher in Y SA and O SA compared with CON (p = .009). Eukaryotic initiation factor 2Bepsilon phosphorylation was 33% and 9% higher in Y SA and O SA compared with CON (p = .04). Translational signaling in young adult and aged plantaris muscle is equally responsive to chronic overload.

Lower extremity power training in elderly subjects with mobility limitations: a randomized controlled trial

BACKGROUND AND AIMS

This study investigated whether high-velocity high-power training (POW) improved lower extremity muscle power and quality in functionally-limited elders greater than traditional slow-velocity progressive resistance training (STR).

METHODS

Fifty-seven community-dwelling older adults aged 74.2+/-7 (range 65-94 yrs), Short Physical Performance Battery score 7.7+/-1.4, were randomized to either POW (n=23) (12 females), STR (n=22) (13 females) or a control group of lower extremity stretching (CON) (n=12) (6 females). Training was performed three times per week for 12 weeks and subjects completed three sets of double leg press and knee extension exercises at 70% of the one repetition maximum (1RM). Outcome measures included 1RM strength and peak power (PP). Total leg lean mass was determined using dual-energy X-ray absorptiometry to estimate specific strength and specific PP.

RESULTS

During training, power output was consistently higher in POW compared to STR for knee extension (approximately 2.3-fold) and leg press (approximately 2.8-fold) exercises (p<0.01). Despite this, PP and specific PP of the knee extensors increased similarly from baseline in POW and STR compared to CON (p<0.01), and no significant time-group interaction occurred for PP of the leg extensors. However, gains in leg press specific PP were significantly greater in POW compared to both STR and CON (p<0.05). Total leg lean mass did not change within any group.

CONCLUSIONS

A short-term intervention of high-velocity power training and traditional slow-velocity progressive resistance training yielded similar increases of lower extremity power in the mobility-impaired elderly. Neuromuscular adaptations to power training, rather than skeletal muscle hypertrophy, may have facilitated the improvements in muscle quality. Additional studies are warranted to test the efficacy of power training in older individuals with compromised physical functioning.

Lower extremity muscle mass predicts functional performance in mobility-limited elders

OBJECTIVES

This study examined the influence of lower extremity body composition and muscle strength on the severity of mobility-disability in community-dwelling older adults.

METHODS

Fifty-seven older males and females (age 74.2 +/- 7 yrs; BMI 28.9 +/- 6 kg/m2) underwent an objective assessment of lower extremity functional performance, the Short Physical Performance Battery test (SPPB). Participants were subsequently classified as having moderate (SPPB score 7: n = 38) or severe mobility impairments (SPPB score

RESULTS

TLM was a strong independent predictor of the level of functional impairment, after accounting for chronic medical conditions, BMD, body fat, body weight and habitual physical activity. In a separate predictive model, reduced muscle strength was also a significant predictor of severe functional impairment. The severity of mobility-disability was not influenced by gender (p = 0.71). A strong association was elicited between TLM and muscle strength (r = 0.78, p < 0.01).

CONCLUSIONS

These data suggest that lower extremity muscle mass is an important determinant of physical performance among functionally-limited elders. Such findings may have important implications for the design of suitable strategies to maintain independence in older adults with compromised physical functioning. Additional studies are warranted to assess the efficacy of lifestyle, exercise or therapeutic interventions for increasing lean body mass in this population.

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Key Words

• aging
• sarcopenia
• mobility
• muscle mass
• strength

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MESH Headings

• Absorptiometry, Photon
• Activities of Daily Living
• Aged
• Body Composition/physiology
• Bone Density/physiology
• Cross-Sectional Studies
• Exercise Test
• Female
• Health Status
• Humans
• Logistic Models
• Lower Extremity/physiology
• Male
• Mobility Limitation
• Muscle Strength/physiology
• Muscle Strength Dynamometer
• Muscle, Skeletal/anatomy & histology
• Muscle, Skeletal/physiology
• Physical Fitness/physiology
• Randomized Controlled Trials as Topic

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Grants

• AG18844 NIA NIH HHS
• R01 AG018844 NIA NIH HHS
• M01 RR000533 NCRR NIH HHS
• R01 AG018844-06 NIA NIH HHS
• M01 RR00533 NCRR NIH HHS

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Muscle fiber size and function in elderly humans: a longitudinal study

Cross-sectional studies are likely to underestimate age-related changes in skeletal muscle strength and mass. The purpose of this longitudinal study was to assess whole muscle and single muscle fiber alterations in the same cohort of 12 older (mean age: start of study 71.1+/-5.4 yr and end of study 80+/-5.3 yr) volunteers (5 men) evaluated 8.9 yr apart. No significant changes were noted at follow-up in body weight, body mass index, and physical activity. Muscle strength, evaluated using isokinetic dynamometry, and whole muscle specific force of the knee extensors were significantly lower at follow-up. This was accompanied by a significant reduction (5.7%) in cross-sectional area of the total anterior muscle compartment of the thigh as evaluated by computed tomography. Muscle histochemistry showed no significant changes in fiber type distribution or fiber area. Experiments with chemically skinned single muscle fibers (n=411) demonstrated no change in type I fiber size but an increase in IIA fiber diameter. A trend toward an increase in maximal force in both fiber types was observed. Maximum unloaded shortening velocity did not change. In conclusion, single muscle fiber contractile function may be preserved in older humans in the presence of significant alterations at the whole muscle level. This suggests that surviving fibers compensate to partially correct muscle size deficits in an attempt to maintain optimal force-generating capacity.