providing almost 100% of his ATP production. Beta oxidation is too slow to provide ATP at the rate required to maintain Jacob's running pace. Aerobic gylcolysis is the only solution. But Jacob wants to go faster because there is an anger is growing in his gut. There must have been something unsettling about the idea of Bella's impending marriage. Jacob starts to run at a speed he cannot maintain indefinitely. Now he requires even more ATP than aerobic gylcolysis can supply and anaerobic glycolysis has to kick in. The problem here is that without oxygen to process the sugar completely, the by-products of anaerobic glycolysis start to cause a burning in Jacob's muscles. You guessed it, lactic acid is being produced and Jacob's muscular thighs are on fire! He shrugs off the pain and pushes on and the anaerobic glycolysis pathway starts to collapse. He has two to four minutes of ATP in this pathway. If it collapses ATP production will drop down to a level that can be maintained by one of the other two aerobic pathways. This will mean that Jacob will be forced to slow down to a pace in sync with lower ATP production. But Jacob doesn't want to slow down. He rips his shirt off and accelerates. All three of the first pathways were trying to keep up the ATP production to help Jacob maintain this all out sprint, but they can't. All that is left is for creatine phosphate to dish-out as much ATP