The work and energetic cost of locomotion. I. The effects of limb mass distribution in quadrupeds

Does limb design influence the cost of locomotion in quadrupedal mammals? If not, morphologists must dismiss the economy of locomotion from consideration when assessing the adaptive factors shaping limb structure. Several studies have recently used externally applied loads to demonstrate a relationship between limb mass distribution and energy costs in human subjects. It is not clear whether a similar correlation would hold for quadrupeds, given their very different gaits. The present study addresses this question by measuring the rate of oxygen consumption in domestic dogs running on a treadmill with mass added either to the limbs or to the back. Trials with no additional mass were used as a control. The use of externally applied loads has the advantage of allowing limb mass to be altered in a system in which other aspects of physiology that might influence cost of locomotion are held constant. The cost of adding mass to the limbs in dogs was found to be significantly greater than that of adding it at the center of mass. Limb mass distribution does affect the cost of locomotion in quadrupeds. A comparison of the results from a variety of studies in which the energetic cost of adding external loads has been measured in animals across a wide size range suggests a qualitative difference in the factors determining the cost of locomotion in large and small animals.