title: Association between fitness and changes in body composition and muscle strength.
abstract: OBJECTIVE
  To examine the association between physical fitness, assessed according to ability and time to complete a 400-m walk, on changes in body composition and muscle strength over a 7-year period.
  
  
  METHODS
  Prospective observational cohort study.
  
  
  METHODS
  Memphis, Tennessee, and Pittsburgh, Pennsylvania.
  
  
  METHODS
  Two thousand nine hundred forty-nine black and white men and women aged 70 to 79 participating in the Health, Aging and Body Composition Study.
  
  
  METHODS
  Body composition (fat and bone-free lean mass) was assessed using dual-energy X-ray absorptiometry in Years 1 to 6 and 8. Knee extension strength was measured using isokinetic dynamometry and grip strength using isometric dynamometry in Years 1, 2, 4, 6, and 8.
  
  
  RESULTS
  Less fit people weighed more and had a higher total percentage of fat and a lower total percentage of lean mass than very fit men and women at baseline (P<.001). Additionally, the least fit lost significantly more weight, fat mass, and lean mass over time than the very fit (all P<.01). Very fit people had the highest grip strength and knee extensor strength at baseline and follow-up; decline in muscle strength was similar in every fitness group.
  
  
  CONCLUSIONS
  Low fitness in old age was associated with greater weight loss and loss of lean mass than with high fitness. Despite having lower muscle strength, the rate of decline in the least fit persons was similar to that in the most fit. In clinical practice, a long-distance walk test as a measure of fitness might be useful to identify people at risk for these adverse health outcomes.
authors.affiliation: Laboratory of Epidemiology, Demography, and Biometry, National Institute on Aging, 7201 Wisconsin Ave, 3C309, Bethesda, MD 20892, USA. kostera@mail.nih.gov
authors.forename: Annemarie
authors.initials: A
authors.lastname: Koster
authors.forename: Marjolein
authors.initials: M
authors.lastname: Visser
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Simonsick
authors.forename: Binging
authors.initials: B
authors.lastname: Yu
authors.forename: David B
authors.initials: DB
authors.lastname: Allison
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Jacques Th M
authors.initials: JT
authors.lastname: van Eijk
authors.forename: Ann V
authors.initials: AV
authors.lastname: Schwartz
authors.forename: Suzanne
authors.initials: S
authors.lastname: Satterfield
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
mesh_terms: D050154:Adiposity / Q000208:ethnology; D001741:Black or African American; D000368:Aged; D000375:Aging / Q000502:physiology*; D001823:Body Composition; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D015999:Multivariate Analysis; D053580:Muscle Strength; D010414:Pennsylvania; D010809:Physical Fitness; D011446:Prospective Studies; D013714:Tennessee; D015431:Weight Loss; D044465:White People