Effects of obesity and sex on the energetic cost and preferred speed of walking

Department of Integrative Physiology, University of Colorado, Boulder, Colorado Submitted 28 June 2005 ; accepted in final form 29 September 2005 The metabolic energy cost of walking is determined, to a large degree, by body mass, but it is not clear how body composition and mass distribution influence this cost. We tested the hypothesis that walking would be most expensive for obese women compared with obese men and normal-weight women and men. Furthermore, we hypothesized that for all groups, preferred walking speed would correspond to the speed that minimized the gross energy cost per distance. We measured body composition, maximal oxygen consumption, and preferred walking speed of 39 (19 class II obese, 20 normal weight) women and men. We also measured oxygen consumption and carbon dioxide production while the subjects walked on a level treadmill at six speeds (0.50–1.75 m/s). Both obesity and sex affected the net metabolic rate (W/kg) of walking. Net metabolic rates of obese subjects were only 10% greater (per kg) than for normal-weight subjects, and net metabolic rates for women were 10% greater than for men. The increase in net metabolic rate at faster walking speeds was greatest in obese women compared with the other groups. Preferred walking speed was not different across groups (1.42 m/s) and was near the speed that minimized gross energy cost per distance. Surprisingly, mass distribution (thigh mass/body mass) was not related to net metabolic rate, but body composition (% fat) was ( r 2 = 0.43). Detailed biomechanical studies of walking are needed to investigate whether obese individuals adopt novel energy saving mechanisms during walking. locomotion; energy cost per distance; cost of transport; economy; body mass distribution Address for reprint requests and other correspondence: R. Browning, Dept. of Integrative Physiology, 354 UCB, Univ. of Colorado, Boulder, CO 80309-0354 (e-mail: raymond.browning{at}colorado.edu )