PONTZER, H.; Harvard University: Linking Locomotor Energetics to Limb Design in Terrestrial Animals.

How does limb design, specifically limb length, affect the energy cost of locomotion? Recently, I proposed a new model linking locomotor cost to limb length for terrestrial animals, and tested the model in humans. Here I present a new study applying this LiMb model across species. Subjects from three species � dogs, goats, and humans � performed walking and trotting/running trials on a treadmill while kinematics and oxygen consumption were recorded. The LiMb model was used to predict the cost of locomotion (COL) from limb length and basic kinematics, and model predictions were compared to observed oxygen consumption. The LiMb model outperformed other predictors of COL, including body mass, Froude number, and contact time. Notably, the model predicted COL equally well both within and between different gaits, species, and locomotor anatomies (i.e., bipeds and quadrupeds). To further test the relationship between limb length and COL predicted by the LiMb model, a larger interspecific comparison was performed using measurements of limb length and transport cost taken from the literature. As predicted, limb length explained over 95% of the variation in cost, with no independent effect of body mass. These results suggest muscular force production during locomotion, and therefore locomotor energy cost, is inversely proportional to limb length for terrestrial animals. This relationship between limb length and COL may be useful for comparisons of locomotor performance both in the field and in the laboratory.