A door rubs or sticks inside a small spot because the extra edge of the jamb is not flat. As you can find there are extensive ways build up impressive strength and size in the lower adominal area muscles, as much, or maybe more than the bench press exercise. https://Klinikandina.org/gretaescalante/6030484/wiki/Tight-Hips-And-The-Domino-Impact-On-Training