When we exercise our muscles contract and produce lactic acid. This acid acts like a ‘poison’ and makes us feel tired.
If this acid is removed from the tired muscle, it can work right again. So, we feel tired after muscular exercise due to the internal ‘poisoning’ of muscles that goes on in the body.
But this is also necessary because only them, the body will take rest. During the rest, the joints of the body replace the supplies of lubricants that have been used by us while exercising.
Below Muscle Pain info from Wikipedia (Read More):-
Myalgia means "muscle pain" and is a symptom of many diseases and disorders. The most common causes are the overuse or over-stretching of a muscle or group of muscles. Myalgia without a traumatic history is often due to viral infections. Longer-term myalgias may be indicative of a metabolic myopathy, some nutritional deficiencies or chronic fatigue syndrome.
The most common causes of myalgia are overuse, injury or stress.[1] However, myalgia can also be caused by diseases, disorders, medications, as a response to vaccination[2] and withdrawal syndromes.[citation needed] It is also a sign of acute rejection after heart transplant surgery.
http://en.wikipedia.org/wiki/Muscle_pain
