Lactic acid, also known as 2-hydroxypropanoic or milk acid, is a compound formed when glucose is broken down under certain conditions in a living creature or by some types of bacteria. In a person, for example, it is an important part of producing energy for strenuous exercise and helps with certain liver functions. During extremely intense exercise, it can buildup to excess and cause short-term burning sensations in muscles. This acid can also be found in certain dairy products, such as yogurt, as well as sourdough breads and some beers and wines as a result of fermentation.
Production and Use in the Body
Skeletal muscles and other tissues commonly produce lactic acid, even while at rest. The body creates this acid as it breaks down carbohydrates to produce energy. The acid only becomes an issue when there are unusually large amounts of it.
This can happen when there is not enough oxygen in the body to completely break down glucose during physical activity. Energy in a person's body is typically created with the assistance of oxygen during aerobic exercise. When oxygen levels reach their limit, but more energy is needed, then the activity becomes anaerobic, which means that energy needs to be produced through other methods. Through a complex process known as glycolysis, glycogen in the muscles breaks down into glucose and then into pyruvate or pyruvic acid.
During aerobic exercise, the pyruvate undergoes an oxidation process that helps remove it. When someone participates in strenuous, anaerobic exercise, however, his or her body does not have the oxygen available to do this. Under these conditions, the excess pyruvate produces lactic acid, which helps generate short-term bursts of energy. A "fight-or-flight" response, for example, often relies on this acid for the energy a person needs to quickly run at high speeds.
Use By The Liver
One common use for lactic acid in a human body is the formation of glucose. Moderate amounts of this acid can move through someone's blood stream and reach the liver, where it undergoes a process called gluconeogenesis to become glucose. This is then either used to maintain healthy glycogen levels within the liver or passed back into the body for use as blood-sugar.
During prolonged strenuous activity, the high amounts of lactic acid may produce hydrogen ions that cause burning sensations in muscles. This is typically quite painful, and many serious athletes and bodybuilders experience this discomfort during intense exercise or weightlifting. The pain is fairly brief, however, and helps prevent serious injury since it usually makes the person stop using a certain muscle group.
A widespread belief among some people is that ongoing muscle soreness following an intense workout is due to a buildup of lactic acid. In truth, most research indicates that only immediate soreness or burning sensations result from too much of this compound. Minuscule tears and inflammation in the muscles usually cause soreness and fatigue that last for several days. Proper training and exercise, including warming up and cooling down muscles, adequate stretching, and a healthy, high-carbohydrate diet, can help prevent injury.
Potential Health Concerns
Very high levels of lactic acid can cause a serious, sometimes life-threatening condition called lactic acidosis. Symptoms of this condition include rapid breathing, sweating, and nausea and vomiting. Healthcare professionals typically draw a blood sample to check acid levels when they suspect a person might have this condition. While extreme over-exercising and overheating can result in lactic acidosis, it can also be caused by alcohol poisoning, liver disease, and a lack of oxygen, due to something like carbon monoxide poisoning.
Use In Food
A number of foods also include lactic acid to alter the pH balance or change the flavor. Certain types of bacteria added to milk, for example, produce the acid, which helps create the texture and tartness found in yogurt. Sourdough bread often relies on both yeast and bacteria in the air around the dough's starter for its tart flavor, usually caused by the formation of acid within the bread. Beer and wine sometimes include bacteria that produces this acid, which can help eliminate other, somewhat unpleasant flavors produced during fermentation.