Calcium is known best of all as a promoter of healthy and strong bones. But it plays a critical role in performance as well. Too little calcium and you can't relax your muscles. Bad relaxation, makes for less potential energy and so on and ultimately for less than satisfactory contraction. Bad contraction equals bad workouts and no growth. Get the picture? By improving relaxation you avoid cramping, injury and twitching. Calcium is also very important in fat metabolization, so no cigar for the people who claim milk is fattening. It makes for less fat storage and better use of present macronutrients in the blood. Using the recommended FDA dosage has shown to decrease body-fat significantly in obese people. It's no secret that the RDV (recommended daily values) were established back in the 60's and 70's for a 2000 calorie diet. I don't know many bodybuilders that grow on a 2000 calorie diet. As a matter of fact I know very few who go below that when dieting. Also the amounts are outdated, so instead of the recommended 1000 mg you should be closer to 2000-2500 mg of calcium daily. Milk can help you get a large part of that. And it's safe to use on a diet too, because of the high calcium content and the not so fattening simple sugar lactose that makes up the carbohydrate portion of milk.