Why Do Muscles Get Tired? - From glycogen to lactic acid
By: Stefan Anitei, Science Editor - Softpedia
The strong and prolonged contraction of a muscle during exercising causes sooner or later muscle fatigue. Researches showed that the fatigue increases while the glycogen stored in the muscles decreases.
The glycogen is a glucose polymer, like an animal starch. When the muscle needs glucose to burn, the glycogen cuts off from its large
macromolecule small molecules of glucose. The glucose is burned with oxygen brought by the blood through the red cells and thus water, carbon dioxide and the energy required by the muscle for producing the contraction result. This is the aerobic respiration (with oxygen, hence the name of aerobic gymnastics).
When there is no glucose (or glycogen) the muscles have problems in executing the work they have to do. Sometimes, after a prolonged muscular activity, the glycogen shortage is also completed by a fatigue of the neuro-muscular plaque, the place where electric impulses transmitted through the nerves are delivered to the muscle. In this case, the efficiency of the muscular contraction decreases.
But in the case of well-fed sportsmen or workers, usually the fatigue is the result of an oxygen shortage. This is especially the case with the bodybuilders. The blood flow to the muscles already does not compensate the oxygen required for extremely intense glucose burnings. In this case, the muscle is forced to appeal to a second type of respiration, called anaerobic, which takes place in the absence of oxygen. This is a reminder that all oxygen-employing organisms once were anaerobic, like many bacteria.
In this case, the burning products are lactic acid, carbon dioxide and energy (but in a smaller amounts than in the case of aerobic respiration). Beside the fact that this respiration is less effective, it also leads to the accumulation of lactic acid, a toxic compound for the muscle cell that blocks its activity.
The lactic acid causes the muscular fever, the intense muscle pain after a hard training. It takes a few days to get out of the muscle and after the effort is gone, the organism can further burn with oxygen the lactic acid to water and carbon dioxide. But remember: lactic acid is also a factor that triggers the muscle's growth (with all the accompanying blood vessels). So that next time a much harder training is required to get again muscle fever.
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Topic: Why Do Muscles Get Tired? (Read 855 times)