I can understand why planks/push ups may not be a great idea. That's in hind sight.
The implants, in my case, are inserted under my pec muscles. No mesh or anything in those days I was a hay carting, tug-of-war winning gym junky when my expanders went in. I could do 50 push ups before I got bored. Lots of pec.
Two days after I'd had them inserted I shot the first one through the incision into my armpit. The second one followed a few weeks later. That was so unusual it wasn't really recognised by the minions in charge over the Xmas break. I got sent home with them just under my skin. Creepy doesn't start to describe that experience. My local BCN took some pics which I sent to my primary surgeon who was on holidays . He hot footed it home and performed the first of several revisions.
Some moves contract your pecs. I never gave that any thought, but I've since squeezed them out, or up, or down two more times. They are now well and truly encapsulated and seem to be stuck in place. Not pretty or comfortable, but they are now relatively stable. Mxx