Upper limits to mass-specific metabolic rates.

An intriguing aspect of animal diversity is the wide range of maximal mass-specific metabolic rates attainable by various species. Metabolic ceilings vary with respect to whether hypermetabolic states involve relatively short bouts of burst or aerobic exercise, or long-term physical activity wherein time-averaged rates of dietary energy intake equal rates of energy expenditure. Design of metabolic flux capacities at the biochemical level can only be meaningfully considered in the context of design at higher levels of biological organization and maximum physiological requirements at the level of the whole organism. Studies of this nature have led to important insights concerning the rules that govern evolutionary design and the constraints that may set upper limits to mass-specific metabolic rates.