Lactic Acid in Muscles After Workouts

Limits of exercise depend on fitness and training of the muscles.
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Lactic acid is often thought of as the baddie in exercise, tiring the muscles and preventing a fitness fanatic from getting the most out of a workout. In fact, lactic acid, or lactate as it's more properly known, is a form of stored energy that the muscle fibers use when they run out of oxygen as fuel. The reason exercise causes the body to breathe more heavily is to fuel the primary energy-producing pathway, but when this pathway uses up available oxygen, the body switches to using alternative energy production which involves the lactate system.


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Back in the 1920s, scientists Otto Meyerhof and Archibald Hill administered electric shocks to the legs of frogs. They knew electricity caused the muscles of the legs to contract, but they found that the electric impulses had no effect on the muscles after a few shocks. This, they thought, was because of the development of lactate in the muscles from the artificial exercising. Sports scientists and physiologists took this for granted for most of the 20th century, never thinking of an alternative role for lactate in energy production.

Origin of Lactate

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In the 1970s, another scientist, Dr. George A. Brooks, challenged this view in his research, where he contended that lactate was not preventing muscular exercise, but rather it was providing the muscles with a source of fuel. When not exercising hard, people convert glucose sugar to a substance called pyruvate, and then uses oxygen to release energy from pyruvate. This is why breathing becomes harder and faster in the gym. After a certain point, though, muscles cannot get enough oxygen to keep the body moving at the same rate, and the body switches to breaking down pyruvate without oxygen. Lactate is derived from pyruvate metabolism.

Function of Lactate

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Lactate production allows the glucose pathway to continue releasing energy for use by the muscles. Rising concentrations of lactate also prevent the body from overexerting the muscles and creating permanent damage, by producing pain signals that tell the person working out to slow down or stop. A rise in lactate is part of the reason gym-goers feel the burn, along with the effects of other products of the metabolism of pyruvate. When the intensity of exercise is lowered or the workout is over, lactate is also converted back into pyruvate for use in the oxygen system again. New research, reported in ABC News, indicates that the presence of lactate also temporarily prevents muscle synapses from becoming overloaded during the few minutes before the burn kicks in, and so gives a temporary boost to muscle function.

Post-Workout Pain

Although a buildup of lactate in muscles creates a temporary burning, "Scientific American" says lactate does not cause delayed onset muscle soreness, or DOMS. A 2006 article in "The New York Times" describes lactate as persisting for only an hour after exercise. The delayed soreness a day or more after a good workout is actually probably due to miscroscopic tears and damage to stressed muscles, and the inflammation of the muscle due to the body's attempt to repair itself.

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