The LiMb model is a new biomechaincal model linking limb design, particularly length, to the energetic cost of locomotion. So far, we've tested this LiMb model in humans, goats, and dogs, testing predicted locomotor cost against observed cost, measured via oxygen consumption. The LiMb model reliably predicts the energy cost of walking and running for a variety of species over a range of speeds, and outperforms other predictors of cost such as contact time and Froude number (PDF).

One interesting prediction of the LiMb model is that the cost to travel a given distance (Cost of Transport, J kg-1 m-1) is a function of effective limb length - the length of the limb as a strut (e.g., "hip height"). Published data on hip height and transport cost bear this out - limb length alone explains over 95% of the variance in transport cost - from ants to elephants (see Pontzer, 2007 J Exp Biol 210).