There is a natural tendency to forget to breathe when doing physical activity which is counter productive to the exertion you are doing. WHen the body exerts itself it requires more energy, and the oxygen that is needed to produce this extra energy. You should make a conscious effort to breathe even more then when you are resting. If you don't breathe adequately you will get tired easily and will increase your likelihood of getting cramps. You should breathe deeply in through your nose and out through your mouth. If someone told you breathing is bad when you are running they are either misinformed or they lied. Did you hear this on FOX? They are notorious for giving out bad information.