Breast Implants Expand Upon Muscle Relaxation?

Two things happen and seem paradoxical. As as the swelling goes down there will be some shrinkage but at the same time as the muscle relaxes your breast projection grows. In general the breast shape and size proportionality improves..Breast implants initially after surgery when placed in a submuscular position often give superior fullness that corrects itself with time, the "fluff and drop" phenomena. In reality the pectoralis major muscle takes a while to adjust its size to accommodate the implant as well as occasional muscle spasm which keeps the implant projection higher than its final resting shape. Additional variables include:laxity of skin, size difference during prior pregnancies, position of implant,size of muscle, and size of implant.As the muscle relaxes the projection of the implant often increases and the breast shape improves. Massage and use of a superior placed elastic strap can often make this process go faster.

Hello,
After the breast tissue and muscles relax the implants can look larger but this varies quite a bit. You can't count on it. The implant volume doesn't change; just the way it looks on you as your tissues adjust to it. This can take 3-6 months in larger cases.

As the chest muscle relaxes, the shape of the breast can change and some women feel as though their breasts get a little larger. As the lower breast relaxes and allows the implant to settle or drop, you lose some of the upper breast fullness and a more natural shape is hopefully achieved. We tell our patients it takes weeks to months to see the final results but follow your plastic surgeon's post-op care/massage instructions carefully. Take care.
Dr Edwards

From your question, are you wondering if when the muscle relaxes and the implants "drop," will there be a breast size change? Keep in mind, the implants themselves do not change, but with swelling considerations and relative implant position changes, the overall breast volume can appear larger or smaller. That is why at least 4-6 weeks must pass after augmentation mammaplasty before final aesthetic judgment as to shape/size can be made.
Hope this helps!