Metabolic recovery in the Desert Iguana (Dipsosaurus dorsalis) following activities of varied intensity and duration

Abstract

Summary Elevated oxygen consumption during recovery is the majority of total metabolic costs associated with short vigorous activity, thus any assessment of total costs associated with such activity should also examine the excess postexercise oxygen consumption (EPOC). This study examined EPOC and total metabolic costs in Dipsosaurus (N = 8; 75 ± 3 g) over a variety of submaximal intensities: 50%, 100% and 400% of the maximum aerobic speed (MAS = 0·27 m s−1; the speed at which V̇O2max is elicited). Activity duration was also varied (15, 60 and 300 s) over these intensities. Total costs increased significantly with both activity intensity and duration. EPOC increased significantly with activity intensity. EPOC increased significantly with activity duration at higher intensities, but not the lowest intensity of 50% MAS. These recovery costs constitute amounts of energy large enough to have an impact on energy budget analyses. The metabolic cost of an individual bout of activity and subsequent recovery was as high as 5% of the predicted daily energy expenditure, an increase of 5–8 × estimates that do not incorporate recovery. To compare the relative economy of different activity regimens, the cost of activity (Cact; ml O2 g−1 km−1), was calculated as total costs, including EPOC, per unit distance travelled. Cact was independent of activity intensity over these ranges, but was inversely related to activity duration. From these data, the most economical strategy to travel a certain distance would utilize a low‐intensity and extended duration, as seen in regular activities such as foraging. High‐intensity activities, such as escape, prey capture or mating behaviours, are thus predicted to be less economical. These should only be observed where metabolic costs would be considered secondary to the more proximal needs of the animal.