>>Does anyone have information on the role of heavy exercise (running several miles every day or two) on lactational amenorrhea and infertility?<< Catherine, Other than the nursing and related hormonal issues that you already know: I don't think that running that is the issue, but rather the amount of body fat. Some women athletes, especially marathon runners and Olympic-level athletes, often work out so much that they become lean, mean, athletic machines with less than normal body fat. A woman's body requires a minimum amount of fat in order to cycle and ovulate, most likely due to the fact that low fat levels historically signified starvation, and the body in turn rejected starting a pregnancy with a poor probably outcome. Please forgive me if you already know this! :-) -Lisa Marasco, IBCLC [log in to unmask] / [log in to unmask]