Usually human body performs only aerobic respiration. But in certain conditions (like heavy exercises), when body needs enormous amount of energy but oxygen supply is not enough, our body gets bounded to perform anaerobic respiration. It occurs in our muscle cells where due to anaerobic respiration, lactic acid gets produced.
You might have experienced pain in arms or legs after doing some heavy physical exercise or work. It is because of accumulation of lactic acid in muscle cells.