"The limiter, therefore, may not be the size of the aerobic bank but the body’s spending habits."
"Imagine you have to water your plants and that if you fill your 5-litre watering can, you will have just enough to do the 5-minute job. Imagine now, that you fill your can but you discover it has a number of holes in the side and is leaking 200 millilitres a minute. You will be lefts short. Is this because the watering can was not big enough or because it leaked? Seal the leaks, and the watering can would be big enough.
The same applies to the repeated shuttles example. If the athlete’s running mechanics were suboptimal, or if turning technique was poor, irrespective or metabolic capacity, the athlete would be spending energy reserves at a much greater rate than a more efficient counterpart. This is the same as the watering-can example. The limiter, therefore, may not be the size of the aerobic bank but the body’s spending habits."
excerpt from HIGH-PERFORMANCE TRAINING FOR SPORTS