I suggest you pay attention to your chest and abdomen when you exercise in the gym. You can exercise your chest and back muscles, such as bench press, dumbbell flying birds, pull-ups and so on. The pectoral and dorsal muscles belong to antagonistic muscles. It's not good to exercise only one of them. Both exercise best. Muscular back is helpful for hunchback. For other breast enlargement exercises, you should consciously hold your head up and chest out at ordinary times, and it will naturally be fine after a long time.