The increased capillaries allow the lactate to escape from the fast twitch fibers to the blood stream. The lactate will be transported to cells which can turn lactate back into pyruvate to be used as a fuel. Slow twitch cells have an especially dense capillary system that functions to deliver oxygen to these cells but also provide lactate for fuel. Increased capillaries also allow the heat built up in the cells from exercise to escape. Increased enzymes .
Endurance training increases several enzymes that help increase aerobic energy production.
While we won't attempt to describe how these enzymes work, one enzyme is extremely important in converting pyruvate into lactate and lactate back into pyruvate. This process helps reduce the body's inventory of lactate. The more of this enzyme that is available, the faster lactate is converted back to pyruvate and the faster it will take lactate from neighboring muscles and the blood stream. The quicker this happens, the faster lactate will leave the fast twitch muscles, thus lessening the acidosis in the fast twitch muscles. This means that these muscles will function at a high rate for a longer time.