Here is an article I came across that you might found useful: Breast Augmentation and the Athlete: What Women Need to Know
Essentially, when it comes to having breast augmentation, you should treat it as an injury and allow plenty of time for recovery and to take it easy.
For athletic women who exercise, usually silicone implants look better under the breast (over the muscle). Implants work best when not impeding muscle movement.
The most favorable position of the implant for very active in women with enough tissue to camouflage it would be subglandular or (preferably) subfascial. That position minimizes downtime, eliminates animation of the pectoralis muscle as a possibility, and does not mechanically affect the muscle function. – Doctor Robert Oliver