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UWL: Association With Outcomes (2009)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
  • To establish the prevalence of sarcopenia in older Americans
  • To test the hypothesis that low skeletal muscle mass, or sarcopenia, is related to functional impairment and physical disability in older persons.
Inclusion Criteria:
  • Participation in the NHANES III cross-sectional survey, conducted from 1988 to 1994
  • Ethnicity of non-Hispanic white, non-Hispanic African American or Mexican American
  • Complete measurements for bioelectrical impedance analysis, height and body weight
  • Non-gravid adults aged 18 and older (older subset defined as those individuals 60 years or older)
  • Civilian
  • Non-institutionalized.
Exclusion Criteria:
  • Ethnicity other than non-Hispanic white, non-Hispanic African American or Mexican American
  • Asian American ethnicity
  • Pregnant women
  • Children younger than 18 years.
Description of Study Protocol:


Stratified, multistage, probability cluster design sampling from US population (See US Department of Health and Human Service.  National Center for Health Statistics. NHANES III Reference Manual and Reports. Hyattsville, MD: Centers for Disease Control and Prevention, 1996 for sampling procedure details.)


Cross-sectional survey.

Blinding Used

Researchers blinded to data collection by virtue of study design.


Standardized home interview and physical examination in a mobile center.

Statistical Analysis  

Descriptive statistics: Mean and standard deviation, multivariate analysis, chi square, multiple logistic regression analysis and odds ratio.


Data Collection Summary:

Timing of Measurements

One point in time for each participant between the years of  1988 to 1994.

Dependent Variables

  • Sarcopenia: Skeletal Muscle Index mean and standard deviation was calculated from NHANES data for persons aged 18 to 39 years. Skeletal Muscle Index is muscle mass over body mass x 100. Muscle mass was derived using bioelectrical impedance analysis and the following equation derived by the primary author: Skeletal muscle mass (kg)= [(height2/BIA-resistance x 0.401) + (gender x 3.825) + (age X -0.071)] - 5.102 (for gender: Male=1, female=0). Skeletal muscle mass index (SMI) was used because it adjusts for stature and mass of other tissues (organs, bone, fat).

    For elderly subjects, classification of sarcopenia included:

    • No sarcopenia if SMI was greater than minus one standard deviation of mean calculated for young adults (aged 18 to 39 years)
    • Class one sarcopenia was present in subjects whose SMI was between minus one and minus two standard deviations of young adult mean
    • Class two sarcopenia was present in subjects whose SMI was below minus two standard deviations of young adult mean. 
  • Functional Impairment: Limitation in mobility performance (e.g., walking, climbing stairs):
    • Assessed via a survey, questions developed by Nagi and Roscow
    • Assessed through an eight-foot walk test, five chair stands and 10-second tandem stand. If an individual was successful on a task, he or she scored a one. If not, he or she got a score of zero
  • Physical disability: Difficulty performing activities of daily living. Subjects were asked if they needed help with personal care needs. Those requiring no help were assigned a score of one while those requiring help were scored a zero.

Independent Variables

  • Age
  • Race
  • Health behaviors  (alcohol consumption, smoking tobacco, physical activity) assessed through in-home interview
  • Comorbidity [major chronic illness such as coronary heart disease, stroke, cancer, lung disease, diabetes mellitus (not GDM), arthritis]  assessed through in-home interview and considered present if subject had ever been told that he or she had any of these conditions.

Control Variables

Body mass index was included as a covariant to determine if SMI predicts disability beyond that predicted by BMI.   

Description of Actual Data Sample:
  • Initial N: 14,818 total subjects, of whom 4,504 subjects were aged 60 years or older                          
  • Attrition (final N): Same as above
  • Age: 60 years and older
  • Location: United States.   
Summary of Results:

Mean SMI±STD in younger men (18 to 39 years, N=3,116) was 42.5%±5.5%; mean SMI±STD in younger women (18 to 39 years, N=3,298) was 33.1%±5.5%.

Body Composition and Prevalence of Functional Impairment and Physical Disability According to SMI in Men and Women Aged 60 Years or Older




Variable Normal SMI (N=1,079) Class 1 Sarcopenia (N=978) Class 2 Sarcopenia (N=167) Normal SMI (N=630) Class 1 Sarcopenia (N=1,374) Class 2 Sarcopenia (N=274)
BMI (kg/m2) 24.7±3.3 28.5±3.3* 32.7±5.1~ 23.1±3.7 27.9±4.7* 33.6±6.2~
Skeletal muscle mass (kg) 29.8±4.2 29.7±4.1 29.0±4.7* 18.2±3.0 17.8±3.2* 17.1±3.9~
Skeletal muscle index (%) 40.6±2.9 34.4±1.7* 29±1.5~ 31.1±2.6 25.3±1.6* 20.5±1.3~

Prevalence of functional impairment: Any reported difficulty (%)

Walking 1/4 mile 16.7 20.8 29.6* 20.2 29.9* 46.6*
Climbing 10 stairs 16.2 16.6 18.2* 18.2 29.4* 49.1*
Carrying 10 lbs 12.0 9.9  17.2* 21.1  27.5* 38.5
Stooping/kneeling/crouching 31.4 41.9* 49.4*  36.6 52.6* 78.2*
Standing up from chair 11.4 14.7 21.0* 14.4 20.6* 37.5*
Unable to:            
Walk eight feet 1.3 1.5 0.8 1.9 2.6 5.8*
Complete five chair stands 2.2 2.3 3.2 3.5 3.4 6.9*
Perform tandem stand 0.7 1.9 4.5* 3.8 2.6 4.2
Prevalence of physical disability (%)            
Any difficulty performing home chores 11.1 12.5 18.5* 20.2 25.4* 38.5*
Any difficulty preparing meals 6.1 4.2 7.0 5.1 8.0 14.1*
Requires help with personal care 3.0 2.9 6.1 5.2 3.6* 8.3*
Requires help with routine needs 4.2 3.5 5.0 6.9 9.2* 12.1*

 * Significantly different from normal SMI group within the same gender (P<0.05).

~ Significantly different from normal SMI group and Class 1 Sarcopenia group within the same gender (P<0.05).

Association Between Sarcopenia, Functional Impairment and Physical Disability in Older (60 years or older) Men and Women

  • To show the associations between functional impairment and physical disability and sarcopenia, odds ratios were calculated before and after adjusting for age, race, BMI, comorbidity and health behaviors
  • After adjustment, class 1 sarcopenia was associated with increased (P<0.05) ORs for having difficulty stooping, crouching or kneeling in both men and women, and men being unable to perform tandem stand. Respective ORs: 1.57 (1.17 to 2.09), 1.49 (1.12 to 2.0), 2.83 (1.17 to 6.88)
  • After adjustment, class 1 sarcopenia was associated with a decreased OR for men having difficulty carrying 10 pounds, women having difficulty performing the tandem stand, and women requiring help with personal care needs. Respective ORs: 0.7 (0.46 to 1.03), 0.47 (0.24 to 1.0), 0.45 (0.27 to 0.77), all significantly less than normal SMI within the same gender (P<0.06)
  • After adjustment, class 2 sarcopenia was associated (P<0.05) with increased ORs for having difficulty stooping, crouching or kneeling and unable to do tandem stand (men). In women, after adjustment, class 2 sarcopenia was associated (P<0.05) with increased ORs for having difficulty climbing 10 stairs; lifting and carrying 10 lbs; stooping, crouching and kneeling standing from a chair; and performing household chores.
Author Conclusion:

The likelihood of functional impairment and physical disability was approximately twice as great in older men and three times as great in older women than in subjects with  normal SMI. These results confirm that age-associated loss of skeletal muscle mass is associated with functional impairment and disability and confirms that sarcopenia is a significant public health problem. 

The results above suggest that modest reductions in skeletal muscle mass with aging do not cause significant impairment. However, if muscle loss progresses to the point where skeletal muscle mass relative to body weight is less than 30% below the mean for young adults, there is a greater likelihood of functional impairment and disability.

Considering that the prevalence of class 2 sarcopenia was 8% in those aged 60 or older, and there are approximately 42 million Americans in this age group, approximately 3.5 million older Americans are at increased risk of functional impairment and disability consequent to low skeletal muscle mass.

Because class 2 sarcopenia was about twice as great in inactive older persons than in older persons who were at least moderately active (three times per week), increasing physical activity should be a treatment goal and prevention strategy for individuals 50 years and older.

Study limitations: Study design precludes a cause-and-effect conclusion. Disability may precede sarcopenia or vice versa.  

Prevalence of sarcopenia may be underestimated due to the fact that institutionalized individuals and those unable to come to the mobile examination center were excluded from the study.


Funding Source:
Reviewer Comments:

No information was provided on subjects race, socioeconomics or geographical region.

For Question #2, it seems that the selection of subjects was free from bias given the sampling procedure. However, due to lack of detailed description of the subjects, it is unclear whether or not by chance the sample population was different from the reference population.

Authors note limitations of underestimating prevalence of sarcopenia, as well as the fact that comorbidity, physical activity participation and physical function were based on self-report.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? Yes
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) ???
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? ???
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? ???
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes