The original shirt, which was bought as a gift was way too small. I had to return it and order a medium. My daughter is quite slender and is in awesome shape. She has swimmer's shoulders and the small size did not fit. You may want to rethink the sizing given that you are selling to swimmer's. She wears a small or extra small in every other shirt she has.
I order a X-Large as a gift for my mom (she is a big phelps fan) however, the jersey is extremely small... the X-Large looks more like a medium... orther than that, the jersey is beautiful.. its a great gift for a skinny person.
I ordered a womens large....it looks very small....I hope it fits my junior girls...xmas presents