Can U Fit Any Size Implant Under the Muscle ?

Yes, there are limits to how large an implant can be placed under and over the muscle for that matter. It all depends on how tight your skin, breast, and muscle tissue are. It also depends on the base diameter of your breast and width of your chest/rib cage. If you have a very tight breast pocket and are narrow chested, then you may want to get a reasonable sized and allow your body to heal.  You can then decide if at some point you want to go bigger.  This may not be advisable though.  It is known that very large implants have a greater chance of having long term complications. Discuss this specifically with your plastic surgeon.

Yes, there are most definitely size limitations.

In general, it's important to match the implant size to the frame size of the patient.   But tissue tightness plays a role too.  So, there is a size limit.  Using an implant beyond this size could increase the risks of tissue thinning, pocket expansion, wound healing problems, future surgeries and revisions.  So, it becomes significantly riskier.

limitations of the volume are not just the muscle..  

how loose is your skin

have you had a pregnance

weight gain and loss

body weight

body size

breast size

chest size