title: Early body composition, but not body mass, is associated with future accelerated decline in muscle quality.
abstract: BACKGROUND
  Muscle quality (MQ) or strength-to-mass ratio declines with aging, but the rate of MQ change with aging is highly heterogeneous across individuals. The identification of risk factors for accelerated MQ decline may offer clues to identity the underpinning physiological mechanisms and indicate targets for prevention and treatment. Using data from the Baltimore Longitudinal Study of Aging, we tested whether measures of body mass and body composition are associated with differential rates of changes in MQ with aging.
  
  
  METHODS
  Participants included 511 men and women, aged 50 years or older, followed for an average of 4 years (range: 1-8). MQ was operationalized as ratio between knee-extension isokinetic strength and CT-thigh muscle cross-sectional area. Predictors included body mass and body composition measures: weight (kg), body mass index (BMI, kg/m2), dual-energy x-ray absorptiometry-measured total body fat mass (TFM, kg) and lean mass (TLM, kg), and body fatness (TFM/weight). Covariates were baseline age, sex, race, and body height.
  
  
  RESULTS
  Muscle quality showed a significant linear decline over the time of the follow up (average rate of decline 0.02 Nm/cm2per year, P < .001). Independent of covariates, neither baseline body weight (P = .756) nor BMI (P = .777) was predictive of longitudinal rate of decline in MQ. Instead, higher TFM and lower TLM at baseline predicted steeper longitudinal decline in MQ (P = .036 and P < .001, respectively). In particular, participants with both high TFM and low TLM at baseline experienced the most dramatic decline compared with those with low TFM and high TLM (about 3% per year vs. 0.5% per year, respectively). Participants in the higher tertile of baseline body fatness presented a significantly faster decline of MQ than the rest of the population (P = .021). Similar results were observed when body mass, TFM, and TLM were modeled as time-dependent predictors.
  
  
  CONCLUSIONS
  Body composition, but not weight nor BMI, is associated with future MQ decline, suggesting that preventive strategies aimed at maintaining good MQ with aging should specifically target body composition features.
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.|Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy.
authors.forename: Elisa
authors.initials: E
authors.lastname: Fabbri
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.
authors.forename: Nancy
authors.initials: N
authors.lastname: Chiles Shaffer
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.
authors.forename: Marta
authors.initials: M
authors.lastname: Gonzalez-Freire
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.
authors.forename: Michelle D
authors.initials: MD
authors.lastname: Shardell
authors.affiliation: Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Zoli
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Studenski
authors.affiliation: Longitudinal Study Section, Translational Gerontology Branch, Intramural Research Program, National Institute on Aging, National Institutes of Health, 251 Bayview Boulevard, Baltimore, MD, 21224-6825, USA.
authors.forename: Luigi
authors.initials: L
authors.lastname: Ferrucci
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology; D001823:Body Composition; D015992:Body Mass Index; D001835:Body Weight; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology*; D009929:Organ Size; D011379:Prognosis
keywords: Aging; BMI; Body composition; Longitudinal study; Muscle quality