I found this very interesting for endurance training and thought I'd share it. It may help to read Lactate Testing - Basic Concepts to understand a few things discussed here.

Endurance training affects lactate metabolism in two fundamental ways.

First, it lessens the production of lactate in slow twitch fibers (called type I fibers) and those fast twitch fibers (called type IIa fibers) which have aerobic capability. Over time, extensive endurance training will convert many of the fast twitch fibers that have almost no aerobic capacity (called type IIb fibers) into type IIa fast twitch fibers.

Second, endurance training speeds up the process of moving the lactate around the muscles and the body, a process that is called clearance. Endurance training causes adaptations that speed up clearance. (See Lactate Physiology and Sports Training- Part 1 for a brief discussion of clearance.)
When an athlete stresses the aerobic system, the body adapts in several ways. Oxygen can move more quickly to each muscle. Oxygen is necessary to produce the maximum amount of energy from pyruvate. Besides the availability of oxygen, there are other important factors which encourage the muscle to use pyruvate for fuel and speed up the use of lactate in adjacent muscles and the blood stream. Four which are enhanced by endurance training are:

Larger mitochondria. Endurance training increases the density of mitochondria in certain cells. Mitochondria are the part of cells that convert pyruvate into energy. The denser they are, the higher the capacity of the cell to use pyruvate as fuel and produce more energy aerobically. Many sports physiologists have used the analogy of a factory to describe mitochondria. When the mitochondria finish processing pyruvate there is a lot of energy available as well as common waste products such as water, carbon dioxide and heat. This process produces a lot of energy but it is too slow to sustain fast activity such as sprinting. Energy produced in the mitochondria will provide most of the energy for a marathon or a triathlon. However, for fast movement, other processes have to be used in addition.
Mitochondria are very dense in slow twitch muscle fibers (Type I) and in some fast twitch fibers (type IIa). There are far fewer mitochondria in type IIb fast twitch fibers. Type IIa fast twitch fibers have the ability to produce aerobic energy while type IIb fast twitch fibers, with very few mitochondria, produce hardly any aerobic energy. Over time, with sustained endurance training, many of the type IIb fibers will convert to type IIa fibers. Since lactate from fast twitch fibers is usually the main source of lactate during exercise, this conversion will cause less lactate to be produced.

Increased capillaries. Endurance training also increases the ability to get the lactate out of the fast twitch fibers and into the slow twitch fibers for processing. With endurance training, the density of capillaries around the muscle fibers is increased, which helps with the clearance and redistribution process. 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.
Endurance training also increases enzymes that facilitate the conversion of pyruvate into energy in the mitochondria. Thus, more pyruvate can be used for fuel. This means that lactate production will be reduced in most muscle cells and that some cells will be able to use more of the lactate produced in other parts of the body. Both these enzymes help speed up the disappearance of lactate.

Increased transporters. Many proteins that help move lactate into and out of cells have only recently been identified. They pick up lactate and transport it across the cell membrane from an area of high lactate concentration to low lactate concentration. (e.g. from fast twitch muscle fibers to the blood stream and the blood stream to slow twitch muscle fibers.) Many of the transporters take both the lactate and the hydrogen ion at the same time which is why they tend to clear at the same rate. The quantity of transporters increases with training. It is another of the important adaptations that take place due to training.
Endurance training is one of the keys to these adaptations that help shuttle the lactate about the body. The faster this shuttling process happens, the better the athlete will perform. So if you hear the expression, "building an endurance base", the changes described above are some of the implications of that expression. Even if the race or game involves an all out effort that requires the use of fast twitch fibers, endurance training has an important place. These fast twitch fibers produce lots of lactate and unless this lactate is cleared out of the fibers and shuttled to other areas of the body the fibers will eventually stop contracting. The longer these fibers can contract the faster the athlete will complete his or her event. So even success in the so called "anaerobic"8 events is affected by the body's ability to clear lactate, which is built through endurance training.

From: http://www.lactate.com/pilact3.html