The production of lactic acid occurs when the body enters a state that requires energy but does not have sufficient oxygen to generate it aerobically. In the world of moving bodies, the rate of respiration increases in an attempt to provide more oxygen to working muscles. There can come a point when the body’s demand reaches a level that exceeds the available supply. In such cases, energy is generated through a process called anaerobic glycolysis in which glucose is broken down or metabolized, resulting in the production of adenosine triphosphate (ATP) and lactic acid. Certain medical conditions can also elevate lactic acid levels.
Also known as milk acid, lactic acid is most often created during periods of dramatic surges in energy demand. For example, an individual who is walking or jogging at a medium pace may suddenly find himself being chased by what he believes to be a vicious dog. The individual will instinctively increase speed to a sprint in an effort to escape and, in the process, require more oxygen than is available. In this instance, the biochemical process of glycolysis will kick into action and result in the production of lactic acid.
Up until the latter part of the 20th century, it was believed that a build up of lactic acid was the cause of muscle soreness. This belief was largely due to the work of Otto Meyerhof, a Nobel laureate who conducted tests on frogs that seemed to indicate that the absence of oxygen in muscles leads to an accumulation of lactic acid, resulting in fatigue. Muscle soreness develops over a period of days, however, and subsequent research has determined that lactic acid is present in the muscle for less than an hour following exertion. Today, lactic acid is viewed as an energy source rather than a waste by-product to be avoided.
Production of lactic acid can also be affected by medical conditions, such as heart disease and infections. If the body goes into shock, blood flow is significantly reduced throughout the body, creating oxygen deprivation. This can result in a life-threatening increase in the production of lactic acid called lactic acidosis. It is in the liver that lactic acid is normally broken down and flushed from the body, so anyone suffering from a diseased or damaged liver can be at particular risk from a sudden increase of lactic acid in the body.