Lactic acid is produced when the body is put through a extended period of hard excercise. At first, the body uses stored ATP and intense ATP production to fuel the body. This process is very effective, however, the ATP process depends heavily on a high supply of oxygen. After a certain time of hard excercise, the respiratory system cannot provide enough oxygen to keep up the rate of ATP use. In this case, the body switches to using lactate from carbohydrates to fuel the body. This process is known as lactic acid fermentation.


Lactic acid was first discovered in 1789 by the Swedish chemist Carl Wilhelm. The acid comes from an experiment which involved isolating an acid in sour milk samples, giving the acid the origin of the name 'lactic'. BY 1810 scientists had increased their knowledge of this acid, finding it in other organic objects, like meat and blood, eventually leading to the finding of the chemical formula for lactic acid in 1833. By 1869 its involvement in fermentation processes had been discovered, and scientists realized that during these processes lactic acid forms in organic tissues (3 ).
Lactic acidosis is when lactic acid builds up in the blood system faster than it can be removed (1 ). This usually happens in moments of intense exercise. During these exercise moments, the body's oxygen level drops to a very low level because the person doing the work is using more oxygen then they can take in. The body then turns to its secondary energy source: lactic acid.
Lactic acid, when coupled with adrenalin, helps to ward off some of the natural effects that the body has to exercise which make it more difficult for the muscles to respond to the signals that they're given. For example, potassium ions are released into the blood when exercise begins, and these ions have a negative effect on the signal receiving ability of the muscles. Lactic acid works together with adrenaline to lessen this effect. Also, lactic acid gives the liver the material it needs to make glucose when there is an oxygen deficiency (4 )


When the body engages in hard excercise, there are multiple processes that the body uses to fuel the excercise. The first burst of energy, lasting about two seconds, comes from a small store of ATP kept in the muscles that is released. Unfortunately, this stored energy runs out quickly. After this, the ATP-PCr system kicks in.
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The main source of energy from the ATP-PCr process comes from the glycolytic system. Glucose and glycogen (a stored version of glucose) are broken down in a series of complex reactions to eventually form energy and pyruvic acid. This acid is then used in the Krebs Cycle, which needs oxygen to produce sustained levels of energy. The Krebs Cycle is a part of the aerobic system, the "engine" that the body uses to maitain excercise over a longer period of time.

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At this point, once gylcolisis is in full use, a lot of pyuvic acid is being produced. The Krebs Cycle can use this acid, but the amount of pyruvic acid that can be used is limited by the amount of oxygen that is taken in. Leftover pyruvic acid is converted into lactic acid. At levels of very high intensity excercise, like a 400 to 600 meter sprint, glycolisis is in overdrive and is producing huge amouts of pyruvic acid. This becomes lactic acid, which can build up quickly inside the muscles. Howver, recent studies have shown that lactic acid is also used as a secondary fuel for excercise in the absence of oxygen. Lactic acid fermentation can help to recharge a part of glycolysis and keep generating ATP (2 ).

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For many years lactic acid has been blamed for the burning sensation n muscles and post - excercise soreness. However, recently studies have found that the bigger factor in soreness and stiffness is micro tears and other damage in muscle fibers. Lactic acid, however, does play a role, as it lowers the pH in the bloodstream around the muscle fiber endings, giving a burning sensation in that area. The best way to deal with lacic acid build up after a workout is to do a cool down - a low effort workout with the purpose of keeping up oxygen flow to the muscles. Oxygen flow helps remove lacic acid quickly (5 ).

The effects of lactic come as a result of running in races such as these, which is why it is a very large problem for track runners. In the 200 meter sprint, which is shown being run by Tyson Gay above, the oxygen source is depleted very quickly. Athletes who have not trained to do strenuous work like this will find it very challenging to perform at a high level, and they will feel their legs getting tired earlier than athletes who have trained for longer periods of time. In these short races the body switches over to other forms of glucose production very quickly, and fatigue begins to set in earlier. The longer the race is the longer it takes for the body to become deprived of oxygen, which is why distance runners tend to have less lactic acid build up after races compared to sprinters.

Distance? or Sprinting?
Distance? or Sprinting?

1) https://health.google.com/health/ref/Lactic+acidosis
2) http://www.runningplanet.com/training/lactic-acid.html
3) http://www.unm.edu/~lkravitz/Article%20folder/lactate.html
4) http://www.coolrunning.com/forums/Forum6/HTML/024151.shtml
5) http://www.brianmac.co.uk/lactic.htm