title: Use of quantile regression to investigate the longitudinal association between physical activity and body mass index.
abstract: OBJECTIVE
  To examine associations among age, physical activity (PA), and birth cohort on body mass index (BMI) percentiles in men.
  
  
  METHODS
  Longitudinal analyses using quantile regression were conducted among men with ≥ two examinations between 1970 and 2006 from the Aerobics Center Longitudinal Study (n = 17,759). Height and weight were measured; men reported their PA and were categorized as inactive, moderately, or highly active at each visit. Analyses allowed for longitudinal changes in PA.
  
  
  RESULTS
  BMI was greater in older than younger men and in those born in 1960 than those born in 1940. Inactive men gained weight significantly more rapidly than active men. At the 10th percentile, increases in BMI among inactive, moderately active, and highly active men were 0.092, 0.078, and 0.069 kg/m(2) per year of age, respectively. The 10th percentile increased by 0.081 kg/m(2) per birth year and by 0.180 kg/m(2) at the 90th percentile, controlling for age.
  
  
  CONCLUSIONS
  Although BMI increased with age, PA reduced the magnitude of the gradient among active compared to inactive men. Regular PA had an important, protective effect against weight gain. This study provides evidence of the utility of quantile regression to examine the specific causes of the obesity epidemic.
authors.affiliation: Division of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Matteo
authors.initials: M
authors.lastname: Bottai
authors.forename: Edward A
authors.initials: EA
authors.lastname: Frongillo
authors.forename: Xuemei
authors.initials: X
authors.lastname: Sui
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: O'Neill
authors.forename: Robert E
authors.initials: RE
authors.lastname: McKeown
authors.forename: Trudy L
authors.initials: TL
authors.lastname: Burns
authors.forename: Angela D
authors.initials: AD
authors.lastname: Liese
authors.forename: Steven N
authors.initials: SN
authors.lastname: Blair
authors.forename: Russell R
authors.initials: RR
authors.lastname: Pate
mesh_terms: D000328:Adult; D000368:Aged; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D006801:Humans; D008019:Life Style; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009765:Obesity / Q000453:epidemiology* / Q000517:prevention & control; D011446:Prospective Studies; D012044:Regression Analysis; D012307:Risk Factors; D011795:Surveys and Questionnaires; D013781:Texas / Q000453:epidemiology
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