Breast Implants Look Deformed when Lifting Weights

Breast implants are placed under the pectoralis muscle AND the breast above it to put as much soft tissue on top of them to hide the implant shell and its ripples. All breast implants ripple but saline implants ripple much more than gel implants.
To be able to place the implants under the muscle, the "C" shaped origins of the pectoralis major muscle are mobilized along the inferior aspect (bottom portion of the C) leaving only the vertical portion which attaches on the sternum bone (dividing this section to get "maximal cleavage" often results in a "Uni-Boob" with communication between the two breast pockets.
While some breast deformity IS to be expected when the muscle shortens and pushes on the implant the extent of your problem May be an incomplete release of the inferior origins of the muscles. The surgeon who operated on you should be able to tell you if this is the case.
Dr. P. Aldea

This is an informed consent issue. I always ask my pre-operative implant patients what activities they participate in. If they are into body building, strenuous exercise, or heavy lifting, I inform them that the action of the pectoralis muscle is to normally 'push' the implants outward. This causes them to look "squished" as you stated.
In some patients, they have enough breast tissue to hide that effect. In your case, you must not, so you see the response to a sub-pectoral implant in action. Options are as follows: Do nothing and accept the result, release the medial insertion of the pectoralis muscle in another operation - this will cause some additional chest muscle weakness, or replace the implants to above the muscle.
Go see your surgeon or additional boarded plastic surgeons to discuss in detail.
Regards from Miami