The Role of Lactate Production in the Metabolic Support of Locomotion by Clawed Frogs Xenopus laevis

Abstract

When African clawed frogs (Xenopus laevis) were stimulated to swim as fast as possible over various distances, the amount of time swimming was a linear function of distance swum. Swimming speed, therefore, was constant and independent of distance with a value of approximately 0.25 m · s−1 (about seven body lengths · s−1). Whole-body lactate was also measured in these frogs as a function of distance swum. These frogs accumulated lactate throughout their bout of swimming, faster initially and then more slowly during the later stages of the exercise. The rate of lactate production decreased with distance traveled but never reached zero. This species, therefore, is dependent on lactate production for a portion of the metabolic support of locomotion throughout a bout of maximum activity. Lactate production accounts for more than 70% of the energy required to support burst activity in Xenopus. The energetic cost of locomotion in Xenopus, calculated from the initial rate of lactate production, is estimated to be 77 J · g · km)−1