I am very healthy, exercise regularly, I don't drink much alcohol, and I don't have hepatitis. There are enzymes contained within muscle cells that can be released into the blood in response to vigorous exercise. It happens in a lot of healthy athletes. Your muscles respond by healing and getting stronger, so that it is harder to injure them next time. Blood banks are cautious and do not want to use blood that may contain hepatitis viruses.
Blood is rejected if it fails to pass all of the tests.
This is to have your individual case reviewed and to look for any signs of disease. Most of these enzymes are cleared from the blood within 2 - 3 days in a properly hydrated individual. So avoiding vigorous exercise for several days prior to donating should help you pass the test. In general there are no physiological benefits to donating blood, but your concern for your fellow man is commendable. Blood banks are always in need of blood and athletes tend to have very healthy red blood cells that are resistant to damage and can carry a lot of oxygen.