title: Advantage of distance- versus time-based estimates of walking in predicting adiposity.
abstract: OBJECTIVE
  Physical activity recommendations are defined in terms of time spent being physically active (e.g., 30 min of brisk walking, 5 d · wk(-1)). However, walking volume may be more naturally assessed by distance than by time. Analyses were therefore performed to test whether time or distance provides the best metric for relating walking volume to estimated total and regional adiposity.
  
  
  METHODS
  Linear and logistic regression analyses were used to relate exercise dose to body mass index (BMI), body circumferences, and obesity in a cross-sectional sample of 12,384 female and 3434 male walkers who reported both usual distance walked and time spent walking per week on survey questionnaires. Metabolic equivalent hours per day (MET · h · d(-1), 1 MET = 3.5 mL O2 · kg(-1) · min(-1)) were calculated from the time and pace, or distance and pace, using published compendium values.
  
  
  RESULTS
  Average MET-hours per day walked was 37% greater when calculated from time spent walking versus usual distance in women and was 32% greater in men. Per MET-hours per day, declines in BMI and circumferences (slope ± SE) were nearly twice as great, or greater, for distance- versus time-derived estimates for kilograms per squared meter of BMI (females = -0.58 ± 0.03 vs -0.31 ± 0.02, males = -0.35 ± 0.04 vs -0.15 ± 0.02), centimeter of waist circumference (females = -1.42 ± 0.07 vs -0.72 ± 0.04, males = -0.96 ± 0.10 vs -0.45 ± 0.07), and reductions in the odds for total obesity (odds ratio: females = 0.72 vs 0.84, males = 0.84 vs 0.92) and abdominal obesity (females = 0.74 vs 0.85, males = 0.79 vs 0.91, all comparisons significant).
  
  
  CONCLUSIONS
  Distance walked may provide a better metric of walking volume for epidemiologic obesity research, and better public health targets for weight control, than walking duration. Additional research is required to determine whether these results, derived in a sample that regularly walks for exercise, apply more generally.
authors.affiliation: Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. ptwilliams@lbl.gov
authors.forename: Paul T
authors.initials: PT
authors.lastname: Williams
mesh_terms: D050154:Adiposity / Q000502:physiology*; D000368:Aged; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D009765:Obesity / Q000503:physiopathology*; D012044:Regression Analysis; D011795:Surveys and Questionnaires; D013995:Time; D016138:Walking / Q000502:physiology*