Final answer:
The lactate threshold is reached when lactic acid production surpasses its clearance, often during high-intensity exercise when anaerobic glycolysis is predominant due to limited oxygen supply.
Step-by-step explanation:
The lactate threshold (LT) is defined as the point at which the rate of lactic acid production exceeds the rate of lactic acid clearance. This occurs when energy demand in muscles is high, and the oxygen supply is insufficient for the complete aerobic metabolism of glucose, forcing the muscles to rely more on anaerobic glycolysis. During this process, pyruvic acid is converted into lactic acid by the enzyme lactate dehydrogenase (LDH). An accumulation of lactic acid in the muscles can lead to fatigue, although it's now understood that lactic acid alone does not necessarily cause muscle soreness. Training can improve the efficiency of anaerobic exercise, potentially increasing the lactate threshold.