The Effect of Exercise on Lactic Acid in Muscles

            For decades it has been a common belief in sports training that lactic acid causes fatigue and that an athlete should train below the “lactic threshold.” Other beielfs about lactic acid in the past are, it builds up in your muscles and makes your muscles burn,  lactic acid buildup is what makes your muscles tire and give out (Kolata, n. pag).

            These misconceptions about lactic acid started in the early years of the 20^th century. In an experiment by Dr. Otto Meyerhoff, a Nobel laureate, cut a frog in half and placed the bottom half in a jar. Of course since the frog was dead, its muscles had no circulation ergo no source of oxygen or energy. Then Dr. Myerhoff gave the dead frog’s leg electric shocks in order to stimulate muscle contration, however after a few twitches, the muscles stopped moving. When Dr. Myerhoff conducted an autopsy, he discovered that frog’s muscles contained high levels of lactic acid. This experiment started the theory that lack of oxygen in muscles leads to the build-up of lactic acid which results to fatigue. (Kolata, n. pag)

            Since then athletes were advised that they should train and exercise aerobically, using only glucose as a fuel. If they exert too much effort they were told that lactic acid would accumulate in the muscles which results to diminished returns in their training. However, numerous researches about lactic acid and its effect on muscles in recent years have shown that these beliefs are actually not accurate.

            In reality, the energy pathway which is responsible for producing most ATP,  adenosine triphosphate, does not require oxygen. This is the glycolytic pathway,  often called anaerobic metabolism since it relies on glycogen, a carbohydrate stored inside muscle cells, as energy source. The glycolytic pathway is comprised by the chemical reactions that produce ATP and generate lactate. This pathway was believed to be separate from the oxidative pathway or aerobic metabolism, which is oxygen-based. (Sanders, n. pag.)

            Recent studies have shown that glycolytic metabolism, which breaks down carbohydrates, and oxidative metabolism, which uses oxygen to break down various fuels, are actually linked by lactic acid. (Sanders, n. pag.)

            According to exercise physiologist and UC Berkeley professor of integrative biology George Brooks, “Coaches and athletes don’t realize it but endurance training teaches the body to efficiently use lactic acid as a source of fuel on par with the carbohydrates stored in muscle tissue and the sugar in blood. Efficient use of lactic acid, or lactate, not only prevents lactate build-up, but ekes out more energy from the body’s fuel.” (Sanders, n. pag.)

            Brooks, along with his colleagues Takeshi Hashimoto and Rajaa Hussien, discovered that carbohydrates is used by muscle cells anaerobically for energy, this process has a byproduct which lactate, however, muscle cells then oxidize the lactate to create more energy. The first cycle is what is known as the glycolytic pathway. This production of energy is what is predominantly utilized during normal exertion. The muscle cells the excrete lactate and goes into the blood to be used as additional source of energy. However, during intense exercise wherein lactate is accumulating rapidly, the second cycle accelerates in order to quickly oxidize the lactate and produce more energy. (Sanders, n. pag.)

            According to Brooks, the mitochondria, also referred to as the powerhouse of the cell, is where lactate is burned to produce energy. The mitochondria needs to become more efficient in burning lactic acid allowing the body to get rid of it before it accumulates to levels that can cause muscle fatigue. This is actually the objective of training. When people train, their bodies are able to get rid of lactic acid more rapidly because at the cellular level, training is actually making the mitochondria grow in the muscle cells. (Sanders, n. pag.)

References

Kolata, G. (2006). Lactic Acid Is Not Muscles’ Foe, It’s Fuel. Retrieved March 20,

            2008, from The New York Times website. http://www.nytimes.com/2006/05/16/health/nutrition/16run.html?_r=1&oref=slogin

Quinn, E. (2008). Lactic Acid and Performance. Retrieved March 20, 2008, from About.com website.

            http://sportsmedicine.about.com/cs/exercisephysiology/a/aa091301a.htm

Sanders, R. (2006). Lactic acid not athlete’s poison, but an energy source-if you know how to use it. Retrieved March 20, 2008, from EurekAlert! website. http://www.eurekalert.org/pub_releases/2006-04/uoc–lan041906.php