As an athlete it is easy to imagine a competitive advantage and increased comfort afforded by reduction of your B-cup breast to an A-cup. We have performed such a procedure on a swimmer, a dancer, and a young runner who needed reduction of just one side for symmetry. Breast reduction is a very flexible procedure and can be tailored to any size breast. For athletic individuals where the breast skin is firm and elastic we will often reduce the breast volume through a small incision under the nipple, much like a breast augmentation incision, and lift the breast tissue and reduce the breast along the under surface keeping an eye on the skin to produce a smooth contour. I have little success with liposuction on a small dense breast. If the skin is loose, even in a small breast, the skin may need to be tailored perhaps by a vertical (lollipop) pattern.
You should stay focused on the potential trade-offs with any reduction of breast volume. First, breast pain on exercise may not go away despite the reduction; just cannot be guaranteed. Second, you may reduce the ability to breast feed, and can risk sensation in the breast. Finally, the scar should be considered if skin reduction is required.
Best of luck,