Unlike other products, BAX-U posture support helps with shoulder retraction without compressing the delicate arteries and nerves. When worn correctly & actively 2 to 6 hours per day for 12 to 24 weeks, over this time you will retrain your nervous system to stand more up right without thinking about it! In clinic this change is called neuro-muscular rehabilitation aka effective change. We are all slouching when we are texting, driving, using computers and even watching TV. ALL these can cause rounding of shoulders. Remember mom slapping you in the back telling you to strand up straight? Since we all have different body types & life styles, BAX-U Posture Support's ability to be adjustable, allows you to be in charge of how much you want your posture to be upright! This is why BAX-u is designed to be adjustable to your body and your lifestyle. TO SIZE: Measuring at the Chest Ribcage measure at lower rib level. Be sure to keep tape level across back and comfortably loose. If you are in between sizes, it is recommended to choose the lower size for women and higher size for men.