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First published online August 22, 2008
Journal of Experimental Biology 211, 2767-2772 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020073
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The effects of gravity on human walking: a new test of the dynamic similarity hypothesis using a predictive model

David A. Raichlen

Department of Anthropology, University of Arizona, 1009 E. South Campus Drive, Tucson, AZ 85721, USA


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  		Fig. 1. Comparison of predicted and observed stride lengths in a sample of humans (N=11). The regression line (solid line) relating predicted and observed stride lengths does not differ significantly from the line of identity [slope (95%CI)=0.87(0.16); intercept (95% CI)=0.23(0.23)]. Broken line is the line of identity (y=x).

 

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  		Fig. 2. Effects of gravity on stride length. Circles are model predictions when gravitational acceleration is altered for both the limbs and the body. Squares are model predictions when gravitational acceleration is altered for the body only. Smaller symbols denote reduced gravity. Gravitational forces are presented as a fraction of earth's gravity (9.81 m s–2). Note that data for a single subject are presented here for clarity. Results for all subjects' models are identical.

 

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  		Fig. 3. Comparison of model predictions with parabolic flight data. Stride lengths calculated at a constant velocity (2 m s–1) for gravity acting on the body and limbs (gray circles) and for gravity acting on the body only (gray squares). Model values are means ±1 s.d. for all subjects. Data from treadmill experiments [open squares (Donelan and Kram, 2001)] and parabolic flights [open circles (Newman, 1996Go)] are presented for comparison. Gravitational forces are presented as a fraction of earth's gravity (9.81 m s–2).

 

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  		Fig. 4. The Froude number at the predicted walk–run transition speed as a function of gravity. Walk–run transition Froude numbers predicted for two conditions: gravity altered for the limbs and the body (gray circles), and gravity altered for the body only (gray squares). Model values are means for all subjects. Data from treadmill experiments [open circles (Kram et al., 1997Go)] presented for comparison. Gravitational forces are presented as a fraction of earth's gravity (9.81 m s–2).

 

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© The Company of Biologists Ltd 2008