Does fermentation in humans happen only in the muscle cell? I read that our MUSCLE cells respire anaerobically sometime to produce little energy and lactic acid as mentioned in this wiki page. https://en.wikipedia.org/wiki/Lactic_acid_fermentation#:~:text=Lactic%20acid%20fermentation%20is%20a,is%20lactic%20acid%20in%20solution. Does it happen anywhere else in our body?