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First published online July 20, 2006
Journal of Experimental Biology 209, 2829-2838 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02316
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The dynamics of hylobatid bipedalism: evidence for an energy-saving mechanism?

Evie E. Vereecke1,2,*, Kristiaan D'Août1,3 and Peter Aerts1,4

1 Laboratorium for Functional Morphology, University of Antwerp, Universiteitsplein 1, Wilrijk B-2610, Belgium
2 Department of Human Anatomy and Cell Biology, University of Liverpool L69 3GE, UK
3 Centre for Research and Conservation, Belgium
4 Department of Movement and Sports Sciences, University of Ghent, Belgium


Figure 1
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  		Fig. 1. In an inverted pendulum (IP) gait, the potential (PE; red line) and kinetic energy (KE; blue line) fluctuate out-of-phase, and energy exchange between PE and KE is possible. If the amplitudes of the PE (FPE) and KE fluctuations (FKE) are similar, there will be an optimal energy recovery via the IP mechanism. In a spring-mass gait, PE and KE fluctuate in-phase and there is no energy transfer between PE and KE. Instead, energy can be stored in elastic tissues during initial stance and released at push-off. This mechanism is active during human running and effectuates an energy recovery of ca. 35%.

 

Figure 2
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  		Fig. 2. Scatter plot showing the variation in velocity and acceleration of all collected bipedal strides (N=43). Only the trials with little or no acceleration (A=0±0.2 m s-2; white band on plot) are included in the statistical analysis. The triangles (at 1 m s-1, 1.5 m s-1 and 2.0 m s-1) indicate the example strides that are illustrated in Fig. 3.

 

Figure 3
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  		Fig. 3. Vertical force component, vertical COM oscillations and energy and power fluctuations during a complete stride of a slow (0.94 m s-1; left), moderate (1.55 m s-1; middle) and fast (2.08 m s-1; right) bipedal sequence. Black horizontal bars on the top graphs indicate the stance phase of each foot; hatched vertical bars indicate the double support phases. For abbreviations, see Table 1.

 

Figure 4
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  		Fig. 4. Scatter plots of the dynamic gait parameters as a function of dimensionless velocity. Filled squares/triangles represent the steady state trials, open squares/triangles represent the `unsteady' trials. Regression lines and equations are only shown for the statistically significant relationships (P<0.05) and include only the steady state trials. For abbreviations, see Table 1.

 

Figure 5
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  		Fig. 5. Angular time profile and power oscillations during a bipedal stride. The top graph shows the 3D joint angles at hip (solid line), knee (squares) and ankle (triangles) of the stance limb (as indicated by the horizontal black bar). The bottom graph shows the power oscillations during the same bipedal stride.

 




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