Lactic Acid: Friend or Foe?

Graph of the lactic threshold (http://www.mfi.ku.dk/ppaulev/chapter18/images/18-4.jpg)

Photo of a Lactic Acid Molecule (http://www.bmrb.wisc.edu/metabolomics/gen_metab_summary_5.php?molName=L_lactic_acid)For decades runners have been concerned with the detrimental effects of lactic acid upon their running intensity. It was believed that lactic acid build up in muscles causes muscle fatigue and soreness, oxygen debt and the burning sensation in runners’ legs. It was considered a dead end waste product that would only be eliminated from the body during recovery periods (“The Myth of Lactic Acid”). Very frequently coaches would have their athletes perform just below their “lactic threshold,” which is the point at which lactic acid begins to accumulate in the muscles during exercise. However, this commonplace thinking is wrong (Morris).
Photo of women marathon runners (http://www.srichinmoyraces.org/us/transcendence/running/worldcc05women)

These theories concerning lactic acid originated during the early 20th century from Nobel laureate Otto Meyerhof. Dr. Myerhoff cut a frog in half and placed the bottom portion in a jar. Since, the frog’s muscles had no circulation or source of energy or oxygen, he gave them an electrical shock to cause muscle contractions. He found that the muscles twitched several times but then stopped moving. After examining the muscles Dr. Myerhoff found that the muscles were covered in lactic acid. From this, the notion that lack of oxygen to muscles and subsequent lactic acid build up causes fatigue originated. This thinking caused athletes to spend most of their effort exercising aerobically, so they would use glucose as fuel. Once they entered the anaerobic zone it was thought lactic acid would begin to accumulate and it was best for the runners to stop (Kolata 2006).

The theory of lactic acid acting as a foe was rarely questioned, until the 1960’s when George A. Brooks, a professor at Berkley, began to take an interest in the subject. Dr. Brooks gave rats radioactive lactic acid and discovered that it was burned faster than any other substance he gave to them. From this testing, Dr. Brooks began to believe that lactic acid was actually a source of energy and was present in the muscles for a reason. However, these new findings were regarded as highly suspect by most scientists, but eventually more evidence began to support Dr. Brooks’ findings (Kolata 2006).

In our bodies our muscles produce lactic acid; however, new research shows that our muscles not only produce but use this lactic acid. It is now believed that glucose is converted first to glycogen and then to lactic acid in muscle cells. Once the glucose becomes lactic acid it is taken up by the mitochondria and used as a source of fuel; it has also been found that mitochondria have a special protein to transport lactic acid (Kolata 2006).
Photo of Mitochondria (http://www.cartage.org.lb/en/themes/sciences/zoology/AnimalPhysiology/Anatomy/AnimalCellStructure/Mitochondria/mitochondria.jpg)

The mass of the mitochondria in a cell increases as a result of intense physical training. Therefore, athletic performance will be improved when a runner works on endurance. Longer more demanding runs increase the mass of mitochondria and consequently the amount of lactic acid that can be metabolized allowing the muscles to work even harder. Therefore, more lactic acid means more muscular endurance, meaning lactic acid is hardly a garbage product in our bodies but it is vital in fueling runners’ bodies (Bosch).

References:
Bosch, Andrew. “Lactic Acid, myths, legends, and reality.” <http://www.time-to-run.com/theabc/lactic.htm>
Kolata, Gina. “Lactic Acid Is Not Muscles’ Foe, It’s Fuel.” 16 May 2006. <http://www.nytimes.com/2006/05/16/health/nutrition/16run.html?_r=1>
Morris, Rick. “Lactic Acid – You Can’t Win Without it” Running Planet. <http://www.runningplanet.com/training/lactic-acid.html>
“The Myth of Lactic Acid.” 20 Nov 2006. <http://www.devinesports.com/Article.7+M576ee0bbeaa.0.html?&cHash=7dad4879b5&tx_ttnews%5bpointer%5d=1>