.Anaerobic threshold is defined as the point during a graded exercise test at which lactate in the blood begins to accumulate faster than it can be got rid of. A fit athlete can maintain an effort at the anaerobic threshold for about 1 hour as long as the blood lactate does not continue to rise. If the intensity of exercise continues to increase from this point, as it would in a graded exercise test, then acidification occurs. This is due to the accumulation of hydrogen ions formed when the lactic acid produced in muscle is converted to lactate. The acidification soon causes a severe muscle fatigue and the intensity of exercise can no longer be maintained.