title: Muscle mass, muscle strength, and muscle fat infiltration as predictors of incident mobility limitations in well-functioning older persons.
abstract: BACKGROUND
  Lower muscle mass has been correlated with poor physical function; however, no studies have examined this relationship prospectively. This study aims to investigate whether low muscle mass, low muscle strength, and greater fat infiltration into the muscle predict incident mobility limitation.
  
  
  METHODS
  Our study cohort included 3075 well-functioning black and white men and women aged 70-79 years participating in the Health, Aging, and Body Composition study. Participants were followed for 2.5 years. Muscle cross-sectional area and muscle tissue attenuation (a measure of fat infiltration) were measured by computed tomography at the mid-thigh, and knee extensor strength by using a KinCom dynamometer. Incident mobility limitation was defined as two consecutive self-reports of any difficulty walking one-quarter mile or climbing 10 steps.
  
  
  RESULTS
  Mobility limitations were developed by 22.3% of the men and by 31.8% of the women. Cox's proportional hazards models, adjusting for demographic, lifestyle, and health factors, showed a hazard ratio of 1.90 [95% confidence interval (CI), 1.27-2.84] in men and 1.68 (95% CI, 1.23-2.31) in women for the lowest compared to the highest quartile of muscle area (p <.01 for trend). Results for muscle strength were 2.02 (95% CI, 1.39-2.94) and 1.91 (95% CI, 1.41-2.58), p <.001 trend, and for muscle attenuation were 1.91 (95% CI, 1.31-2.83) and 1.68 (95% CI, 1.20-2.35), p <.01 for trend. When included in one model, only muscle attenuation and muscle strength independently predicted mobility limitation (p < .05). Among men and women, associations were similar for blacks and whites.
  
  
  CONCLUSIONS
  Lower muscle mass (smaller cross-sectional thigh muscle area), greater fat infiltration into the muscle, and lower knee extensor muscle strength are associated with increased risk of mobility loss in older men and women. The association between low muscle mass and functional decline seems to be a function of underlying muscle strength.
authors.affiliation: Institute for Research in Extramural Medicine, VU University Medical Center, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands. m.visser@vumc.nl
authors.forename: Marjolein
authors.initials: M
authors.lastname: Visser
authors.forename: Bret H
authors.initials: BH
authors.lastname: Goodpaster
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Kritchevsky
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Michael
authors.initials: M
authors.lastname: Nevitt
authors.forename: Susan M
authors.initials: SM
authors.lastname: Rubin
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Simonsick
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D000368:Aged; D000375:Aging / Q000208:ethnology* / Q000502:physiology; D044383:Black People / Q000706:statistics & numerical data; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D015331:Cohort Studies; D016001:Confidence Intervals; D005260:Female; D015577:Geriatric Assessment; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000208:ethnology / Q000503:physiopathology*; D009142:Musculoskeletal Physiological Phenomena; D010809:Physical Fitness; D011237:Predictive Value of Tests; D011336:Probability; D011379:Prognosis; D011446:Prospective Studies; D016059:Range of Motion, Articular / Q000502:physiology; D018570:Risk Assessment; D016138:Walking; D044465:White People / Q000706:statistics & numerical data