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Trade-offs between speed and endurance in the frog Xenopus laevis : a multi-level approach
1 Laboratory of Functional Morphology, Department of Biology, University of
Antwerp, Universiteitsplein 1, Wilrijk B-2610, Belgium
2 School of Science and the Environment, Coventry University, D Block,
Priory Street, Coventry CV1 5FB, UK
* e-mail: rwilson{at}uia.ua.ac.be
Accepted 30 January 2002
One of the most interesting trade-offs within the vertebrate locomotor system is that between speed and endurance capacity. However, few studies have demonstrated a conflict between whole-animal speed and endurance within a vertebrate species. We investigated the existence of trade-offs between speed and endurance capacity at both the whole-muscle and whole-animal levels in post-metamorphs of the frog Xenopus laevis. The burst-swimming performance of 55 frogs was assessed using a high-speed digital camera, and their endurance capacity was measured in a constant-velocity swimming flume.
The work-loop technique was used to assess maximum power production of whole peroneus muscles at a cycle frequency of 6 Hz, while fatigue-resistance was determined by recording the decrease in force and net power production during a set of continuous cycles at 2 Hz. We found no significant correlations between measures of burst swimming performance and endurance capacity, suggesting that there is no trade-off between these two measures of whole-animal performance. In contrast, there was a significant negative correlation between peak instantaneous power output of the muscles at 6 Hz and the fatigue-resistance of force production at 2 Hz (other correlations between power and fatigue were negative but non-significant). Thus, our data support the suggestion that a physiological conflict between maximum power output and fatigue resistance exists at the level of vertebrate muscles. The apparent incongruence between whole-muscle and whole-animal performance warrants further detailed investigation and may be related to factors influencing both whole-muscle and whole-animal performance measures.
Key words: trade-off, constraint, locomotion, performance, muscle, power output, fatigue resistance, frog, Xenopus laevis
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