When one runs very fast in a short time, the body becomes tired. This fatigue is caused by lactic acid.
It is a thick material which forms when muscle cells change sugar or glycogen into ready energy. After a short rest period, the body recovers and one is ready to run again.
Animal glycolysis is a process in which simple sugar and glycogen are changed to lactic acid and energy is given off. This occurs when oxygen is not readily available so that the body can continue to function. As the acid accumulates, some gets into the blood and its presence causes deeper and faster breathing. Part of theacid (C3H6O3) is oxidized to CO2, H2O and O2. Finally, the muscle and liver tissue can use this released energy to change lactic acid back to sugar.
Sour milk contains lactic acid produced by the lactic acid bacilli important hi the fermentation processes.
