Modeling the Metabolic Energetics of Brief and Intermittent Locomotion in Lizards and Rodents1

Abstract

When locomotor activity is brief, physiological steady state conditions are not attained. It is therefore difficult to model the energetic costs of intermittent activity using standard methods. This difficulty is addressed by considering as reflective of the metabolic costs of activity not only the oxygen consumed during the activity itself, but also the excess post-exercise oxygen consumption (EPOC) and any excess metabolites persisting at the end of EPOC. This paper briefly reviews the metabolic events associated with EPOC, and then examines how this approach can be applied to address questions of how behavioral variables associated with locomotion (activity duration, intensity, frequency) can influence the energetic costs to the animal per unit distance. Using data for lizards, mice, and others, EPOC can be shown to be the major component of energetic costs when durations are short, regardless of exercise intensity. Brief activity is much more expensive by this measure than is steady state locomotion, regardless of phylogeny or body mass. Three studies of intermittent locomotion provide evidence that brief behaviors can be undertaken at lower metabolic costs than predicted from single bouts of activity when repeated in a frequent, repeated pattern. Metabolic savings appear greatest when the pause period between behaviors is short relative to EPOC duration, the time for organismal metabolic rate to return to pre-exercise levels, although longer pause periods may increase endurance.