Lactic acid is NOT a muscle illness.

Definiton= the anaerobic production of lactic acid from glucose.

Yes, both are. During exercise lactic acid is produced faster than the tissues ability to remove it resulting in an excess of lactic acid. This results in the "burn" felt in your muscles. The by-products of the metabolization of glucose are heat and lactic acid.

Lactate (also known as lactic acid) and NAD+

Lactic acid fermentation is an anaerobic process. This means that lactic acid is produced in the absence of oxygen. This usually occur in bacteria cells but can also occur in muscle cells.