|Weyand, Peter -|
|Smith, Bethany -|
|Puyau, Maurice -|
|Butte, Nancy -|
Submitted to: Journal of Federation of American Societies for Experimental Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2010
Publication Date: December 1, 2010
Citation: Weyand, P.G., Smith, B.R., Puyau, M.R., Butte, N.F. 2010. The mass-specific energy cost of human walking is set by stature. Journal of Federation of American Societies for Experimental Biology. 213:3972-3979. Interpretive Summary: Understanding the energy cost of walking is important to the health. We know that children and short adults use more energy walking on a per kilogram body weight than taller individuals. In this study, we sought to test if height explains the apparent body-size dependency of energy cost of walking. We measured energy expenditure and stride lengths at six walking speeds in 48 children and adults who varied in height, age and weight. We found that the most comfortable walking speeds measured to be equivalent among shorter and taller individuals. At the individuals’ preferred walking speed, stride lengths were directly proportional to height and the energy cost per stride was the same. We concluded that the weight-specific energy cost to walk a distance equal to one’s height is the same for children and adults. This relationship provides a simple way to estimate the energy cost of walking across a wide range of body sizes.
Technical Abstract: The metabolic and mechanical requirements of walking are considered to be of fundamental importance to the health, physiological function and even the evolution of modern humans. Although walking energy expenditure and gait mechanics are clearly linked, a direct quantitative relationship has not emerged in more than a century of formal investigation. Here, on the basis of previous observations that children and smaller adult walkers expend more energy on a per kilogram basis than larger ones do, and the theory of dynamic similarity, we hypothesized that body length (or stature) explains the apparent body-size dependency of human walking economy. We measured metabolic rates and gait mechanics at six speeds from 0.4 to 1.9 ms-1 in 48 human subjects who varied by a factor of 1.5 in stature and approximately six in both age and body mass. In accordance with theoretical expectation, we found the most economical walking speeds measured (J kg-1 m-1)to be dynamically equivalent among smaller and larger individuals. At these speeds, stride lengths were directly proportional to stature whereas the metabolic cost per stride was largely invariant. The tight coupling of stature, gait mechanics and metabolic energy expenditure resulted in an inverse relationship between mass-specific transport costs and stature. We conclude that humans spanning a broad range of ages, statures and masses incur the same mass-specific metabolic cost to walk a horizontal distance equal to their stature.