The reason more mitochondria don't always mean that you run faster (
instead of longer) is because (1) you may have far more mitochondria than necessary to process the maximum amount of
oxygen your lungs can take in and your red blood cells
transport at any given time, (2) regardless of how many mitochondria you have, the motor neurons connected to your aerobic muscle fibers are smaller than those connected to your anaerobic muscle fibers.