title: Changes in physical activity and body composition in postmenopausal women over time.
abstract: OBJECTIVE
  Higher physical activity (PA) has been associated with greater attenuation of body fat gain and preservation of lean mass across the lifespan. These analyses aimed to determine relationships of change in PA to changes in fat and lean body mass in a longitudinal prospective study of postmenopausal women.
  
  
  METHODS
  Among 11,491 women enrolled at three Women's Health Initiative clinical centers who were selected to undergo dual-energy x-ray absorptiometry, 8352 had baseline body composition measurements, with at least one repeated measure at years 1, 3, and 6. PA data were obtained by self-report at baseline and 3 and 6 yr of follow-up. Time-varying PA effect on change in lean and fat mass during the 6-yr study period for age groups (50-59 yr, 60-69 yr, and 70-79 yr) was estimated using mixed effects linear regression.
  
  
  RESULTS
  Baseline PA and body composition differed significantly among the three age groups. The association of change in fat mass from baseline and time-varying PA differed across the three age groups (P = 0.0006). In women age 50-59 yr, gain in fat mass from baseline was attenuated with higher levels of PA. Women age 70-79 yr lost fat mass at all PA levels. In contrast, change in lean mass from baseline and time-varying PA did not differ by age group (P = 0.1935).
  
  
  CONCLUSIONS
  The association between PA and change in fat mass varies by age group, with younger, but not older, women benefiting from higher levels of aerobic PA. Higher levels of aerobic activity are not associated with changes in lean mass, which tends to decrease in older women regardless of activity level. Greater attention to resistance training exercises may be needed to prevent lean mass loss as women age.
authors: Stanford Prevention Research Center, Department of Medicine, Stanford University, Stanford, CA 94305-5411, USA. stsims@stanford.edu
authors: Stacy T
authors: ST
authors: Sims
authors: Jessica
authors: J
authors: Kubo
authors: Manisha
authors: M
authors: Desai
authors: Jennifer
authors: J
authors: Bea
authors: Jeannette M
authors: JM
authors: Beasley
authors: Joann E
authors: JE
authors: Manson
authors: Matthew
authors: M
authors: Allison
authors: Rebecca A
authors: RA
authors: Seguin
authors: Zhao
authors: Z
authors: Chen
authors: Yvonne L
authors: YL
authors: Michael
authors: Shannon D
authors: SD
authors: Sullivan
authors: Shirley
authors: S
authors: Beresford
authors: Marcia L
authors: ML
authors: Stefanick
mesh_terms: D015502:Absorptiometry, Photon; D000273:Adipose Tissue / Q000502:physiology; D000368:Aged; D000369:Aged, 80 and over; D001823:Body Composition / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008875:Middle Aged; D017698:Postmenopause / Q000502:physiology*; D011446:Prospective Studies