The cost of muscle power production: muscle oxygen consumption per unit work increases at low temperatures in Xenopus laevis Daudin

Metabolic energy (ATP) supply to muscle is essential to support activity and behaviour. It is expected therefore that there is strong selection to maximise muscle power output for a given rate of ATP use. However, the viscosity and stiffness of muscle increases with a decrease in temperature, which means that more ATP may be required to achieve a given work output. Here we test this hypothesis in Xenopus laevis acclimated for four weeks to 15oC (cold) or 25oC (warm) and tested acutely at both temperatures. Cold acclimated frogs had greater sprint velocity at 15oC than warm acclimated animals. However, acclimation temperature did not affect isolated gastrocnemius muscle biomechanics. Isolated muscle produced greater tetanus force, faster isometric force generation and relaxation, and produced more work loop power at 25oC than at 15oC acute test temperature. Oxygen consumption of isolated muscle at rest did not change with test temperature, but oxygen consumption while muscle was performing work was significantly higher at 15oC than at 25oC. Muscle therefore consumed significantly more oxygen at 15oC for a given work output than at 25oC. The metabolic cost of muscle performance and activity therefore increases with a decrease in temperature. To maintain activity across a range of temperature, animals must increase ATP production or face an allocation trade-off at lower temperatures. Our data demonstrate the potential energetic benefits of warming up muscle before activity, which is seen in diverse groups of animals such as bees that warm flight muscle before flight, and humans performing warm ups before exercise.