Energetics of isometric contractions as a function of muscle temperature

The energetic cost of generating isometric force in isolated frog muscle was examined at 10, 20, and 30 degrees C. Recovery O2 consumption (delta O2) and recovery lactate production (delta Lact) were measured under conditions in which O2 was not limiting metabolism. Both increased linearly with the force-time integral (integral of Fdt) generated by the muscle. The slopes of the regression equations for both delta O2 and delta Lact as a function of integral of Fdt increased with increasing temperature with a temperature coefficient (Q10) near 3. Total high-energy phosphate resynthesis from recovery metabolism was calculated by scaling the delta O2 regression equation and the delta Lact regression equation into equivalent ATP units and summing them. This total recovery metabolism was modeled as the sum of two components, a "cost of maintaining force" (slope of the equation) and a saturable "start up cost" (intercept of the equation). The cost of maintaining force increased with temperature with a Q10 near 3 over the whole temperature range, whereas the start up cost was nearly independent of temperature between 0 and 20 degrees C and fell to near zero at 30 degrees C. Delta O2 measurements from a series of tetani given in rapid succession showed that for contractions subsequent to the first, no start up cost was incurred and that the "cost of generating force" for these contractions was equal to the slope of the regression line for single tetani. The practical consequence of these facts is that, in series of tetani, the cost of generating force increases with a Q10 of 3.