I think the sizing must be off on the cups. I'm a large 34B (use to be a large 34C then I had kids. ah, kids. :) and this wasn't tight in the cup area. I did some jumping jacks to test and I was bouncing all over the place. Not cool.  So...I'm going to try sizing down to see if that alleviates the bounce, as the bra feels fabulous! Now it would make a great medium impact sports bra, but I'm not in the market for one of those. The other Moving Comfort bra I have is the Fiona. Very nice and supportive. Love, love, love, but want a t-back. I'm loving the feel of Moving Comfort bras, but not liking the sizing issue.