Lactic anaerobic metabolism
The biochemical process of lactic anaerobic source consists in transforming the muscular glycogen, without oxygen, into the cytoplasm of cells (out of mitochondrias). It produces lactic acid in form of H+ ion and lactate. It is not directly the lactate but the H+ ion which is responsible of the efficiency loss of contractile elements of muscle.
This process is unable to use the entire glycogen reserves, it is stopped when acidosis becomes too high. To improve it, it is important to increase the muscular capability to support a high acidosis, and the blood capability to transform the lactate.
The aerobic source is important for this process because more the aerobic power is high, more the lactate increases slowly. It allows also the recycling of lactate.
To eliminate the lactate after an effort, it is rather efficient to pursue a medium effort (active recovery) than to stop down (passive recovery). In this case, the recovery delay is four times lower.
The lactate is neither a poison, nor a scrap. It is an intermediate product, rich in energy, used by the heart and the lightly used muscles (ATP regeneration) and the liver (glycogen regeneration).
The lactaemia is the lactate concentration into the blood and not into the muscle. It is often used to measure an effort, but is only an indirect and very incomplete representation of muscular acidosis. Its usage is delicate because the maximum value is obtained in a variable delay after effort stopping (5 to 10 min). It is only interesting for the follow-up of training effect for the same sportsman with the same event.
By another way, the "anaerobic threshold" notion, defined in laboratories by a 4 mmol/l lactaemia, has no biological or experimental sense. It is often used abusively to define an hypothetical limit between the anaerobic metabolism and the aerobic metabolism corresponding to the maximal muscular acidosis.