There has been several athletic women who undergo breast augmentation, and one of the important questions they typically ask is "when can I go back to the gym and exercise?" One of the key elements is that one must not exercise immediately after any type of procedure, including breast augmentation.
To understand why one would be careful when it comes to working out a few weeks after surgery, one should understand how the body would heal after surgery.

Fast Facts about Wound Healing & Breast Augmentation
Pectoralis Muscle (Chest wall muscle) Strength after a Breast Implant
Signs that You Have Workout Too Much
Potential Consequences if One Works Out Beyond Their Limits after a Breast Augmentation
Resuming exercise after breast augmentation can be particularly challenging. One should ask your plastic surgeon for any advice regarding their exercise protocol after a breast enhancement procedure. If one experiences pain after a particular exercise activity, I recommend to stop performing that certain activity and resume 1-2 weeks later.
Houston Breast Augmentation

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de Haan A, Toor A, Hage JJ, et al. Function of the pectoralis major muscle after combined skin-sparing mastectomy and immediate reconstruction by subpectoral implantation of a prosthesis. Ann Plast Surg. 2007 Dec;59(6):605-10.