We have two ways to make ATPs, or the major source of energy molecules in our bodies: Aerobic and anaerobic respiration. Aerobic respiration takes place in the presence of oxygen in a cell. Using carbohydrates, like glucose, and oxygen, we make 34-38 ATP molecules, carbon dioxide, and water. This is used in our daily lives and long runs, like the marathon, 100km, or even the 100 mile races because this is a more efficient way of energy production than the other way. Anaerobic respiration, on the other hand, produces only 2 molecules of ATP, and it is only carried out without the presence of oxygen, like when we are sprinting. Using only glucose, we make 2 ATPs and lactic acid. That is why we feel sore after a sprint or a bench press the next day: due to lactic acid.
I have made a graph of the average speed of all the fastest run for each distance, starting from 100 meters to 100 miles(approximately 160934.4 meters). We can see that as runners start to run longer, they rely on mostly the aerobic respiration because it is more efficient.
We can conclude from this graph that the maximum rate of aerobic respiration can enable humans to run 9 mph max for a long time.
