Would implants over the muscle be a mistake or possibiity for me? I run and lift weights.

If you have little breast tissue, I recommend placing the implants behind the muscle for better upper breast fullness and coverage.

You can elect to go over the muscle or under. The weight of the implant over time can lead to sagging. Under the muscle may help with this somewhat. Depending on the implants that interest you your surgeon may suggest using mesh to support your tissues and prevent bottoming out. Silicone does tend to feel more like natural breast tissue than saline, but that's just an opinion. Rippling and wrinkling can happen with any implant, but is more common with saline. The more breast tissue you have, the more these irregularities are disguised by your native tissue. I encourage you to discuss these concerns further with your surgeon.

Dear Anon453054,
I almost always place implants submuscular. It lowers the rate of capsular contracture significantly. In addition, it looks much more natural because the muscle provides covering over the implant so its not as round on the top. I've also noticed the implants drop less over time when they are protected under the muscle.
Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery