Exercise performance of reptiles.
From the vantage point of thirty years of study, we can sketch the general features of activity capacity and performance ability in reptiles. Extant reptilian groups all share low levels of maintenance metabolism and ectothermy, with their consequent advantages (Pough, 1980) and disadvantages. Among the latter is a limited capacity to expand aerobic metabolism, limited in comparison to the relatively great costs of terrestrial locomotion. Particularly at low body temperatures, reptiles outstrip their aerobic capacities with any exercise more intense than a slow walk. Anaerobic metabolism, particularly anaerobic glycolysis, can be used to fuel bursts of intense activity. As a consequence, however, physiological disruption and exhaustion are entailed. Under field conditions, many reptiles alternate long periods of quiescence or slow movement with very brief bursts of exertion. Other ectotherms with a similar pattern of metabolism have been shown thereby to extend performance beyond that supportable by either aerobic or anaerobic metabolism alone (Weinstein and Full, 1992). Even with careful alternation between these metabolic modes, reptiles remain particularly prone to exhaustion during vigorous activity, as least as judged by our mammalian frame of reference. Their capacities for burst activity and exertion have been shown, at least in some species, to be important determinants of their natural survival.