Do you know Why do muscles ache after exercise because When you exercise your muscles contract and produce an acid known as lactic acid. This acid acts like a poison’. The effect of this lactic acid is to make you tired, by making muscles feel tired. If the acid is removed from a tired muscle, it stops feeling tired and go right to work again.
So feeling tired after muscular exercise is really the result of a kind of internal poisoning that goes on in the body. But the body needs this feeling of tiredness so that it will want to rest. During rest the joints of the body replace the supplies of lubricants they have used up.