chrismar, I don't know if I understood your question right, but I'll try to give an answer.
To maintain a certain speed, you need a certain amount of energy (ATP). And yes, aerobic metabolism is more efficient than anaerobic metabolism with regard to harvesting the energy stored in glucose. You get 2 mol ATP per 1 mol glucose using anaerobic metabolism (glycolysis) vs a theoretical 38 mol ATP per 1 mol glucose when using aerobic metabolism (2 from glycolysis, 2 from the Krebs cycle, and about 34 from the electron transport system). (Note: Theoretical, because the cellular respiration is not 100% efficient, and thus the ATP-yield is slightly lower than 38:1 for aerobic metabolism - the maximum is closer to 28-30 ATP molecules.)
Using either aerobic or anaerobic metabolism doesn't mean you change the energy requirement for maintaining your speed, only how much ATP you get from each mole of glucose. Thus, assuming a certain energy requirement, you need more glucose when using anaerobic metabolism, but this is so because in anaerobic metabolism you are only able to release a smaller amount of the energy which is in the glucose molecule compared to when you metabolize the glucose aerobically. The remaining energy is not "lost", but will be found in the lactate molecule which is formed from the pyruvate that is the end product of glycolysis. The energy in lactate can be used when oxygen is once again available (and aerobic metabolism dominates).
The energy you use will not differ between aerobic/anaerobic metabolism, but you will need to have a high anaerobic rate to produce the same number of ATP:s, meaning that you will fatigue faster.
Don't know if this made any sense...?
/Johan
