Scientists have made an interesting experiment about fatigue.
When a muscle in the body works, it produces lactic acid,and it is this lactic that makes the muscle tired.
Fatigue is not just a chemical process, it is also a biologicai process. We can't just "remove" fatigue; we must allow the cells of the body to rest. Damages must be repaired, nerve cells of the brain must be "recharged," the joints of the body must replace used-up lubricants. Sleep will always be necessary as a way of restoring the body's energy after fatigue.
However, a person who has been working hard at his desk for hours may not want to lie down at all when he is tired. He'd rather take a walk! Or when children come home from school they want to run out to play... not to lie down and rest.
The reason is that if only a certain part of the body is tried the best way to make that part feel fresh again is to make other parts of the body active! We can actually rest by means of activity. Of course, if you are totally exhausted, the best thing to do is to go to sleep!
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