ENERGETICS OF BIPEDAL RUNNING I - METABOLIC COST OF GENERATING FORCE

Similarly sized bipeds and quadrupeds use nearly the same amount of me tabolic energy to run, despite dramatic differences in morphology and running mechanics. It has been shown that the rate of metabolic energy use in quadrupedal runners and bipedal hoppers can be predicted from just body weight and the time available to generate force as indicated by the duration of foot-ground contact, We tested whether this link b etween running mechanics and energetics also applies to running bipeds . We measured rates of energy consumption and times of foot contact fo r humans (mean body mass 78.88 kg) and five species of birds (mean bod y mass range 0.13-40.1 kg). We find that most (70-90 %) of the increas e in metabolic rate with speed in running bipeds can be explained by c hanges in the time available to generate force, The rate of force gene ration also explains differences in metabolic rate over the size range of birds measured. However, for a given rate of force generation, bir ds use on average 1.7 times more metabolic energy than quadrupeds. The rate of energy consumption for a given rate of force generation for h umans is intermediate between that of birds and quadrupeds. These resu lts support the idea that the cost of muscular force production determ ines the energy cost of running and suggest that bipedal runners use m ore energy for a given rate of force production because they require a greater volume of muscle to support their body weight.