Why does one implant move with muscle flexing?

It's possible that the implants would be distorted asymmetrically by exercising the pectoralis muscle with a sub muscular augmentation. There's the outside possibility that one implant was placed above the muscle what that's highly unlikely. More than likely this is a modest asymmetry and nothing to worry about.

Thank you for your question.  I believe what you are describing is the "animation deformity" that exists when implants are placed beneath the muscle of the chest.  As you flex, the muscle squeezes down in a diagonal direction from your breast bone towards your shoulder. When this contraction happens, the implant underneath the muscle is moved downward and outward.  This only occurs when you move your chest muscle, and the implant returns to its previous position when the muscle contraction stops.  Unfortunately some women notice this more than others, and in your case apparently on one side more than the other. I would speak with your plastic surgeon about this, as he can give provide reassurance and perform a physical exam to ensure this is what is taking place. 

Hello amyrn. Congratulations on your breast augmentation. You have very large breast implants and any small muscle movement will be far more noticeable under the circumstances. The condition you have is called animation. I don't believe there is anything that you did wrong. Our bodies were not designed to have a breast implant under the muscle despite the obvious benefits. Your PS can go back an release more muscle, but the potential side effect of doing is is bottoming out. Unless the condition is very noticeable, it might not be worth the risks. Discuss your concerns with your PS. Best wishes, Dr. ALDO