When oxygen levels are low, like during a sprint, your body will attempt to create more energy anaerobically. Because the products for glycolysis eventually run out, there is a secondary process called fermentation that helps to replenish those products, and allows some cells to function for a short period of time when oxygen levels are low. During fermentation, the pyruvate made during glycolysis converts to lactic acid, which can build up in your muscles, causing soreness and fatigue.
