To do this exercise you must be in cardiovascular shape or else it can be dangerous because it raises your blood pressure. Do squads while you do inspiration and when you go up do expiration. After you do this regurarly you see your penis tissues become a lot stronger. Another exercise is to use bodybuilding belt for one or two hours, it strenghtens your diaphragm and urogentinal area. Do also chi kung exercises (iron shirt). After this exercises, be careful in penis exercises because it dilates a lot more.
God Bless!
God Bless!