High glucose flux saturating pyruvate dehydrogenase (PDH) can cause pyruvate to convert to lactate.

“And in my opinion, acts as a fuse in the body. From an evolutionary perspective, if the body sees there's a lot of high flux of glucose, the body might mean, hey, what's going on here? We need to stop it because it's not good to become hypoglycemic. And maybe the majority of those glycolytic enzymes in the downstream action of glycolysis, they usually have a high Michaelis constant. But when they get to PDH, it's like a fuse. So when that fuse goes, then pyruvate is converted to lactate.”