Why do my implants have a crease in the center when I flex? I feel deformed. (photos)

Hi, Gl2.  Congratulations on your surgery! And boy, can you every flex!!!!!!!!  As others have answered, the creasing that you are experiencing is due to the muscle edge adhering to the implant capsule and your breast tissues/skin that may occur with submuscular or dual plane placement.  In some cases, a limited or partial creasing may occur due to incomplete muscle release.  In other cases, the creasing may result from upward migration of the muscle edge with over expansion of the lower portion of the breast and descent of the implant.  And in many cases, it is just part of the healing and scarring process (with thinner tissues increasing the risk of such healing).  
Many surgeons will recommend placing the implants above the muscle (subglandular) in body builders for this very reason.  However, placing the implants above the muscle in an individual with thin tissues (typical of body builders with low body fat percentage) will result in a more obvious show of the implant, often with a sharp demarcation between the thin chest and sudden implant border.  The upper pole contour with the submuscular/dual plane placement, in my opinion, is smoother and usually in a higher, more-supported, and attractive position.  
Best of luck on whatever you decide!

In the United States breast implants are most commonly placed 'under the muscle'.  This practice began in the early 1990's when the FDA placed a moratorium on the use of silicone gel breast implants for cosmetic use.  Saline implants are a little more wrinkly and crinkly than silicone implants.  Placing implants behind the pectoralis muscle adds a layer of thickness, maybe 1/4 to 1/2 inch, between the skin and the breast implant.  This thickness is nice to have in the upper part of the breasts.  It makes it less likely that wrinkles in the implants will be visible to other people when the patient is wearing a bra, bathing suit, or low cut top.  Perhaps the largest "downside" to placing implants under the muscle is exactly what you are showing in your photographs.  When the pectoralis muscles contract this creates a deformity, sometimes called an animation deformity.  We talk to patients about this during the consultation process.  Placing implants in front of the pectoralis major muscles eliminates this possibility.  However, when the implants are in front of the muscles they are now closer to the skin, and this makes it more likely that wrinkles in the upper parts of the implants will be noticeable to other people.  In other parts of the world breast implants are more commonly placed in front of the muscle.  However, other countries did not have a moratorium placed on the use of silicone implants.  Silicone implants remain the most commonly used implants in countries outside the US.  Because they are less wrinkly they may be less likely to develop rippling that is easily noticed to other people.  However, that also depends on the size of the implants being used and how thick a woman's naturally existing tissue is. Visit with the surgeon who placed your implants and show that surgeon what you are showing us in your photographs.  If this motion bothers you enough you may find it worth looking into having the implants placed in front of the pectoralis major muscles.