About muscle flex deformity. Can it get worse or better with time?

It's a good question. Some women who have implants placed under the muscle can develop an animation deformity. When the pectoralis muscle activates it pushes the implant down and out. I would address this issue with your plastic surgeon to determine how best to proceed. Actively working out your chest with benchpress or push-ups will push your implant down and out and can stretch the lower pole of the breast.

Thank you for the question. Unfortunately, it is not possible to predict whether the "animation deformity" will improve with time.  In my opinion, this animation or flexion deformity is the only potential downside of the sub muscular (dual plane) position of breast implants (compared to the sub glandular position). In my practice, I have observed that as breast implants fully "settle", that the animation deformity does seem to improve. Your plastic surgeon will always be your best resource when it comes to more precise information/advice. Best wishes.