The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Minimum cost of transport and optimal velocity: what variables are predictive?


Anthropology, University of Washington, Orthopaedics and Sports Medicine, University of Washington

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Cost of transport (CoT) is the amount of energy that an individual uses to move a given distance, and for most extant animals, CoT has a minimum value (minCoT) that occurs at the optimal velocity. When applied to extinct species, this minimum is often used as a proxy of locomotor efficiency, because it represents the least energy that can be used to move. While much is known about the correlates of CoT in extant creatures, little work has been done to determine which, if any, morphological features predict minCoT and optimal velocity.

To rectify this, the energetic expenditure of 15 women was measured as they walked at 5 self-selected velocities. Standard anthropometrics were also measured. To this sample was added existing data from 79 people (including 44 children). Optimal velocity and minCoT for each individual was determined from the first derivative of the best-fit curve between velocity, velocity squared and CoT. Body mass predicted 66% of the variability in minCoT (r2=0.66, p<0.001), but hip width (r2=0.61, p<0.001) and calf circumference (r2=0.58, p <0.001) were also effective. Optimal velocity was predicted by leg length (r2=0.56, p<0.001).

From this, it seems clear that while the locomotor effectiveness of a person is influenced by their mass, how fast and, therefore, how far they move is a function of their leg length. If this trend holds for fossil hominins, size differences need to be interpreted as indicators not simply of locomotor effectiveness, but also of daily range.

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