what is the specific reason for muscle cramp that are caused due to sudden physical exercise?

when you exercise, the muscular sugar and lactic acid levels change drastically. to neutralise this some times you may have lie down breath with mouth, which supplies more oxygen. else severe muscle cramps result. thats why exercise level has to be increased slowly and while competition also can show for a short while more activity... not for longer. when feel thirsty dont drink more water... first lay down, stretch legs and breath more this will balance the lactic acid you can just wet your lips later you can drink more water so providing more oxygen is more important in exercise

stressing your muscles too much,,,

first of all either you are doing your exercise just within an hour after you eat something or else your are doing it all wrong... from your name i would consider you are an Indian... so if you are doing these exercise in gym.. then either change your gym or else trainer cause they are not paying proper attention and if you are doing it home.. then take proper guidance.....

and while you feel a muscle pull or cramp just relax that area.. try not to move that part... and lay down or just sit back if you can

Stressing the muscle(s).

Lack of hydration , iron and potassium