Meeting Abstract
For many animals, the transition from walking to running occurs at a specific speed, but it is unclear what factors trigger gait changes. While the most widely accepted function of gait transitions is the reduction metabolic cost, it is not obvious that there is a metabolic trigger signaling animals when to switch gaits. In humans, gait transitions also function to decrease dynamic instability, which, as measured by stride duration variability, increases with speed and results in greater metabolic costs. While these patterns are known in humans, similar studies have not been conducted in other mammals. This study explores the relationships between the energetic costs of locomotion and stride variability at and around the preferred walk/run transition speed in two mammalian species (Sapajus apella and Didelphis virginiana). For each subject, the preferred walk/run gait transition speed was determined as animals moved quadrupedally on a treadmill. Once the preferred gait transition speed was determined, energetics and stride variability were calculated at 0.045 m/s intervals above and below this speed. In both species, stride variability and energetic cost increased as animals approached the walk/run transition, and subsequently dropped after animals moved into a run. However, the reduction in stride variability was more closely associated with the preferred walk/run transition speed, and the metabolic benefits occurred later. We propose that animals use proprioceptive information to monitor stride variability and trigger gait transitions to maintain dynamic stability. Metabolic efficiency is clearly an important benefit of gait transitions, but reduction in dynamic instability may be the proximate trigger determining when those transitions occur.
