A smooth breathing pattern will rid your body of the carbon dioxide and bring in fresh air with lots of useful oxygen. It is very important to know when it is okay to be breathing heavy and when its not. If you are just starting and breathing heavy, you are starting too fast, slow down and let your body warm up. When you are running up a hill plan on an increase in your breathing unless you slow your pace or walk. When you are doing intervals expect to breathe heavily, just let your breathing go back to normal before starting the next interval.
Distance running has to be a very comfortable rhythmic activity.
It isn t about enduring pain, it is about pacing yourself painfree. You can use your breathing as a signal, like having a heart rate monitor on. Expect an increase in your breathing rhythm when you increase your pace. If your body is ready for the faster pace, your breathing will adjust. If it doesn t, you will need to slow down until it does.