RESEARCH Mechanics & Cost of Walking and Running

 

 

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Our bipedal locomotion is a defining character of the human lineage, dating back to our earliest ancestors. But why did this peculiar form of locomotion evolve, and how did it affect hominin behavior and ecology over time? Work in our lab investigates the mechanics and energetics of locomotion to understand the links between anatomy and performance, in order to reconstruct the locomotion and ecology of fossil hominins.



Limb Length & Locomotor Cost
It is often assumed that natural selection will act to maximize the economy of locomotion and other activities in order to maximize the energy available for growth and reproduction. However, recent modeling efforts suggest that selection to improve locomotor economy in terrestrial animals is strongly dependent on foraging efficiency (see image above). For most living species, selection for additional improvement in locomotor economy appears to be quite low, because the foraging efficiencies they obtain are already quite high.

Papers & Presentations

Pontzer, H. 2007. Limb length and the scaling of locomotor cost in terrestrial animals. Journal of Experimental Biology. 210, 1752-1761.

Pontzer, H. 2007. Predicting the cost of locomotion in terrestrial animals: a test of the LiMb model in humans and quadrupeds. Journal of Experimental Biology 210, 484 - 494.

Modeling Locomotion in Fossil Hominins
Applying laboratory-tested models of walking and running gait and cost to the hominin fossil record allows us to understand how extinct species moved about the landscape and used their habitat. Our modeling efforts suggest that bipedalism likely provided little, if any, energetic advantage for early hominins: the number of legs used to walk and run has no effect on cost. However, it appears that selection did favor improved locomotor economy after bipedalism evolved, with evidence from the australopith pelvis indicating a more efficient gait than is seen in living apes. We have also applied this approach to modeling cost in dinosaur locomotion.

Papers & Presentations
2009 Pontzer, H., Allen, V., Hutchinson, J.R. 2009. Biomechanics of running indicates endothermy in bipedal dinosaurs. PLoS ONE

2009
Pontzer, H., Raichlen, D.A., Sockol, M.D. 2009. The metabolic cost of walking in humans, chimpanzees, and early hominins. J Hum Evol. 56, 43-54

2008 Raichlen, D.A., Pontzer, H., Sockol, M.D. The Laetoli footprints and early hominin kinematics. J Hum Evol. 54, 112-11
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C
ollaborators: David Raichlen, John Hutchinson

Determinants of Cost in Terrestrial Locomotion
Following on experimental work in other labs in the 1990's, our work on the metabolic cost of locomotion in terrestrial animals has shown that energy cost is driven primarily by the volume of muscle activated each step to support body weight. The primary anatomical determinants of cost are therefore: body weight (heavier animals use more energy), limb length (longer limbs reduce the energy spent per kg body mass), muscle fasicle length (long muscles are more expensive), and the effective mechanical advantage of the limb joints (better mechanical advantage means lower cost). Current efforts are examining how these anatomical variables interact, and how mechanical work contributes to cost.

Papers & Presentations
2009 Pontzer, H., Raichlen, D.A., Sockol, M.D. 2009. The metabolic cost of walking in humans, chimpanzees, and early hominins. J Hum Evol. 56, 43-5

2007 Pontzer, H. Limb length and the scaling of locomotor cost in terrestrial animals. J Exp Biol. 210, 1752-1761.

2007 Pontzer, H. Predicting the cost of locomotion in terrestrial animals: a test of the LiMb model in humans and quadrupeds. J Exp Biol. 210, 484 - 494

2005 Pontzer, H. A new model predicting locomotor cost from limb length via force production. J Exp Biol. 208, 1513 – 1524

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Collaborators: David Raichlen
This work has been supported by the National Science Foundation

Ecological Pressures and Energy Budgets
Classic life history theory suggests that energy budgets (the amount of energy used each day by an organism) are a fixed function of body size, and that differences in growth and reproduction rates reflect differences in energy allocation within this fixed budget. Our recent work suggests that, in fact, energy budgets can expand or contract over evolutionary time in response to ecological pressures. Expanding the energy budget provides more energy for reproduction but increases energy needs and the risk of starvation; contracting the energy budget reduces the energy available for reproduction but decreases ecological risk. Our current work is exploring how ecology affects the evolved energy budgets of humans, apes, and other mammals.

Papers & Presentations
2011 Pontzer H., Raichlen D.A., Wood B.M., et al. Hadza forager energetics and the evolution of the human metabolic strategy. AJPA. S52, 242

2010 Pontzer, H., Raichlen, D.A., Shumaker, R.W., Ocobock, C., Wich, S.A. Metabolic adaptation for low energy throughput in orangutans. PNAS. 107, 14048-52.

2009 Pontzer, H., Kamilar, J.M. Great rangin
g associated with greater reproductive investment in mammals. PNAS.106, 192-196.
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This work has been supported by the National Science Foundation and the Wenner Gren Foundation