FIG. 40.4

How is metabolic rate affected by running speed and body size?

BACKGROUND In the 1970s and 1980s, the American physiologist C. Richard Taylor and his colleagues performed studies on the relationship between metabolic rate and running speed in mammals of different sizes. They were interested in understanding the energetic costs of running in different animals.

EXPERIMENT Taylor and colleagues measured oxygen consumption during running for a wide range of organisms. They trained each animal to run on a treadmill at different speeds and measured oxygen consumption using either a face mask or enclosure. Oxygen consumption was used as a measure of metabolic rate.

RESULTS The researchers found that there is a linear increase in metabolic rate with speed in different-sized animals and that larger animals expend less energy per unit body mass to move a given distance compared to smaller ones, as shown on the graph.

FOLLOW-UP WORK Similar studies were performed with kangaroos, which move by hopping rather than running. Interestingly, it was found that it is “cheaper” (that is, it requires less energy) to hop than to run. This finding perhaps explains why kangaroos and other hopping animals survived, while many animals that run on four legs became extinct in Australia 30,000 to 20,000 years ago with the arrival of early humans. Studies have also compared the energetic costs of running on two legs and running on four legs, with the finding that the cost is the same.

SOURCES Dawson, T. J., and C. R. Taylor. 1973. “Energetic Cost of Locomotion in Kangaroos.” Nature 246:313–314; Taylor, C. R., N. C. Heglund, and G. M. O. Maloiy. 1982. “Energetics and Mechanics of Terrestrial Locomotion.” Journal of Experimental Biology 97:1–21.