title: Efficiency of walking and stepping: relationship to body fatness.
abstract: OBJECTIVE
  To determine energetic efficiency of walking and stepping in a heterogeneous normal adult population and its association with body fatness and to assess within- and between-individual variations.
  
  
  METHODS
  Using a combination of a whole-room indirect calorimeter and a large precision force platform, we simultaneously measured minute-by-minute energy expenditure (EE) and mechanical work during walking and stepping in healthy adult men (n = 60) and women (n = 85). Efficiency was calculated as a ratio (percentage) of mechanical work and EE of activity. Efficiency of walking and stepping performed at various intensities was compared for reproducibility within the same day (morning and afternoon) and correlated with a subject's characteristics.
  
  
  RESULTS
  The efficiency of walking was negatively correlated with body fatness in both men and women at 0.9 to 1.2 m/s but positively correlated with body fatness in men and not correlated in women at the slowest speed tested (0.6 m/s). Efficiency of walking and stepping of various intensities was reproducible during the same day. Compared at similar EE levels, walking was more efficient than stepping (26% to 27% vs. 18% to 22%, p < 0.01). Women were significantly (p < 0.01) more efficient than men during stepping. Age, sex, body mass, fat-free mass, fitness (maximal oxygen uptake), height, and speed variations contributed to the between-subject differences in efficiency.
  
  
  CONCLUSIONS
  Obese individuals were less efficient than lean individuals during normal-speed walking. Significant interindividual variations in efficiency of walking and stepping may be attributed to habituation and physical characteristics such as age, sex, and fitness level.
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN 37232-2279, USA. kong.chen@vanderbilt.edu
authors.forename: Kong Y
authors.initials: KY
authors.lastname: Chen
authors.forename: Sari A
authors.initials: SA
authors.lastname: Acra
authors.forename: Candice L
authors.initials: CL
authors.lastname: Donahue
authors.forename: Ming
authors.initials: M
authors.lastname: Sun
authors.forename: Maciej S
authors.initials: MS
authors.lastname: Buchowski
mesh_terms: D000328:Adult; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D002153:Calorimetry, Indirect; D003430:Cross-Sectional Studies; D004734:Energy Metabolism / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D015203:Reproducibility of Results; D018709:Statistics, Nonparametric; D016138:Walking / Q000502:physiology*