Gait Change

The energy expenditure of a dog on a treadmill is measured at different gaits

Caleb M. Bryce

Land animals change their gait as they increase speed, from walking to trotting or running [see “Making Tracks” by Bernd Heinrich 2/19]. Some researchers have hypothesized that animals change gait when it is energetically most efficient to do so. Others have argued that animals alter their pace in order to move quickly with more stability, with less chance of injury or falling. A recent study tested these two hypotheses—whether animals change gait to conserve energy or to reduce instability–by observing various animal species running on treadmills.

A team of researchers, led by Michael Granatosky of the University of Chicago, trained Virginia opossums, Didelphis virginiana, tufted capuchins, Sapajus apella, and domestic dogs of several different breeds to run on a treadmill while inside a plexiglass box that measured their metabolic rate. The researchers measured the speed at which the animal changed from walking to running, the time between strides (how long it took for the same leg to hit the ground twice), and the amount of energy consumed (based on the changes in oxygen consumption and carbon dioxide production). Similar data for four other mammalian species and two additional bird species were drawn from previously published work.

The researchers found that only four of the nine examined species used less energy after switching from walking to running. Just as many species showed no change in energy expenditure after switching their gait. Furthermore, most of the tested species did not change gait at their energetically-optimal transition speed: Some species walked when it would be more energy efficient to run, and others ran when walking would conserve more energy. These results suggest that energy conservation is not a universal determinant of gait change.

In contrast, all but one of the examined species showed more consistent stride times, indicating greater stability, after beginning to run. All eight of these species showed the least stability at the transition to running, suggesting that stability, not energy expenditure, is the more important factor determining gait change.

Further research in a greater variety of species and settings may shed more light on the importance of stability in triggering a change of gait. Because this study relied on data from animals running on treadmills, it is uncertain if the findings hold for animals running in naturalistic settings. Preliminary analysis of data from ostriches running in the wild suggest that they, too, change gait to prioritize stability rather than to save energy. (Proceedings of the Royal Society B)