Reappraisal of energetics of locomotion shows identical cost in bipeds and quadrupeds including ostrich and horse

Abstract

Animals use different amounts of energy to move from place to place depending on their size and mode of locomotion ¹. Flyers and swimmers use less energy to move a unit mass a unit distance than do running animals, and small animals use more energy than large ones. For terrestrial animals Taylor et al.² have defined cost of transport as the slope of the regression line relating weight-specific metabolic power and running speed. Cost of transport, so defined, is a comparative index of the relative energy-cost of locomotion of different animals. Fedak et al.³ had reported that bipeds and quadrupeds have different costs and that, extrapolating from their data, the difference between them would be greatest among large animals. Now, after considering new data from 100-kg ostrich and horse, and reviewing the data collected in the past 5 yr, we find that there are no consistent differences in energy-cost between bipeds and quadrupeds of any size. The apparent differences reported earlier was biased by an unfortunate choice of animals. The new, much more extensive, evidence shows no difference of the scaling of energy requirements for locomotion between bipeds and quadrupeds, but suggests a difference between apparently clumsy and graceful animals.