Metabolic Costs Of Generating Force :: essays research papers

ENERGETCS OF BIPEDAL RUNNING 1. METABOLIC COST OF GENERATING FORCE Summary Similarly sized bipeds and quadrupeds use nearly the same amount of metabolic 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 time available to generate force as indicated by the foot ground contact. We tested whether this link between running mechanics and energetics also applied to running bipeds. We measured rates of energy consumption and times of foot contact for humans (mean body mass 78.88kg) and five species of bird mean body mass 0.13-40.1 kg). We find that most (70-90%) of the increase in metabolic rate with speed in running bipeds can be explained by changes in the time available to generate force. The rate of force generation also explains differences in metabolic rate over the size range of birds measured. However, for a given rate of force generation, birds use on average 1.7 times more metabolic energy than quadrupeds. The rate of energy consumption for a given rate of force generation for humans is intermediate between that of birds and quadrupeds. These results support the idea that the costs of muscular force production determines the energy cost of running and suggest that bipedal runners use more energy for a given rate of force production because they require a greater volume of muscle to support their body weight. Key words: locomotion, energetics, bipedal, bird, muscle force. Introduction The question of wither more energy is required to run on two or four legs was addressed 100 years ago when Zuntz (1897) performed some of the first measurements of metabolic energy consumption in running animals. He found that horses used less energy than humans to move a unit body weight a unit distance, and he speculated that there might be an energetic benefit to moving on four legs rather than two. However, subsequent measurements of oxygen consumption in running dogs showed that these quadrupeds use more energy per unit body mass to move a given distance than both humans and horses. Zuntz (1987) noticed that this energy cost of transport in horses, dogs and humans was proportional not to limb number but to body mass and concluded that, per unit body weight, small animals use more energy to run a given distance than do large animals, regardless of limb number (Zuntz, 1987).