Blood lactate and training to improve threshold

Type II muscle fibers oxidize lactate at a very fast rates. When muscle contraction produces a significant amount of lactate, it is then released into the central circulation of the blood, and within seconds it is made available to that muscle for energy. Therefore, 75% of the lactate produced from high intensity exercise is made available for energy production in type II muscle fibers. The remaining 25% of lactic acid is used for energy in the heart, …

…At high intensity exercise there is not enough 02 provided. Thus you slip into anaerobic metabolism, which involves the breakdown of glucose to pyruvic acid and lactate acid without the presence of 02. This makes up the difference and supplies additional energy to your muscles to keep them going. There are several different types of AT training that one can do to enhance the oxygen delivery system, including Long Fast Distance Variable Pace, Fartleks, and Tempo runs.