The anaerobic threshold is the point during exercise at which the body starts to produce lactic acid faster than it can be removed. This occurs when the intensity of the activity exceeds the capacity of the body to supply oxygen to the muscles. As a result, the body shifts from aerobic metabolism, which uses oxygen, to anaerobic metabolism, which does not. At the anaerobic threshold, physical performance can decline, and fatigue sets in more quickly. Athletes often train to increase their anaerobic threshold, allowing them to sustain higher intensities for longer periods. This training can improve overall endurance and performance in various sports.