Although I cannot give you advice specific to your situation, generally speaking there should be no problem working out the pectoral muscles 5 years after breast augmentation surgery. You may want to check with your own plastic surgeon to see if he/she has any other thoughts.
Keep in mind...
Capsular contracture refers to scar tissue which can form around breast implants making the breasts feel firm or creating shape changes in the breasts. The exact causes are unclear, but appear to be related to inflammation and the formation of a thick collagen lining around the breast...