Your lower sternum does have some indentation/depression to it. The belly sticking out may make it look a little deeper than what it is but not signifcantly so. Exercise is not the solution to a depressed lower sternum, adding volume by fat transfer or a small sternal implant are the treatment...
In the case of torn pectoral muscles, implants are very effective. Essentially the implant just fills in the gap left by the torn muscle and everything looks normal. I perform this routinely from patients around the world. In some cases I colaborate with an orthopedic surgeon...
Oval pec implants generally enhance more of the lower part of the pectoral / chest area where as the vertical-rectangular pec implants enhance more uniformly the lower and upper chest toward the collar bone as well as along the middle of the chest from top to bottom. There is no one is...