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Why do we feel fatigue in our muscles during physical activity?
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With vigorous exercise, your muscles use anerobic energy and build up lactic acid. That is what causes the pain. Rest for a bit, the lactic acid gets reconverted to other forms of energy, and it doesn't get tired anymore.
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Well if your a beginner your body isn't use to all the work and exercise,but the more you work out the better it will get.
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They run out the cellular energy that gets them to contract...it's called ATP (AdenoTriPhosphate?). Once you deplete your stored amount of ATP, your body starts to retrieve it from fat and stuff. Eventually, you run out of ATP, and your muscles will let you know your out of it by getting very tired. Once the ATP rejuvinates, your muscles will be ready to go again!
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lactic acid
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There are a couple different reasons why muscels get tired after exercise. One is due to an insuficent or runing out of ATP, or in other words the thing that gives muscles the energy to contract. . . Another reason is oxygen debt, when excersing you need a constant supply of oxygen to allow muscles to contract. When you exercise, your oxygen suppy is used up and your body may not be able to keep up with the amount of oxygen needed. . . There can also be lactic acid build up due to this, which is kind of the cramping feeling you get sometimes during exercise. If you have a lot of lactic acid it does not allow your muscles to contract due to a low ph level.. . As well as the fact that you need a good blood supply, remember you also need blood and oxygen in other parts of the body, so by exercising you are taking away oxygen and blood from other areas of the body that also rely on blood and oxygen. Your body is working hard to balance the differnet parts of your body that need these things. . . All of this is know as muscle fatigue.
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