Figured I'd give a comparison review for the sizing difference.I read the reviews and chose to order a size up. (Large)Bust is 34b, but on the small side of that b, rib cage under the ladies is 32 inches.Laying flat the champion measures a hair over 13 1/2. There is not much stretch, really pulling it got to 16 inches.My under armour pictured is a size medium. Same measurements, so the champion does run small.I personally love under armour, however I really liked this champion over it. The under amour is cut differently which gives me the ugly armpit/ side fat sometimes seen when you wear sports bra. It is also a tighter of a fit in the chest than the champion. Might be how champion has the back cut away on this bra that gives you the more roomier feel. But I didn't feel squished into the champion, which I loved. Supportive but not restrictive. I also like the way the back is more narrow than traditional sport bras, which with all the cute colors they come in, might make it look better to wear in the summer with a tank, instead of the awkward ugly spread of a traditional racer back in a spaghetti strap top.The only thing I didn't like about this bra was the elastic band at the bottom, I didn't notice it when I was working out, but when I got done and went to remove the bra, the band collected all the sweat, which was soaked and kinda gross. I was not expecting a cool wet band when I went to grab it. Which isn't the worst thing, but it's not something I really experienced with a bra before.I don't know how supportive this would be with cardio or running, I'm a gym rat that lifts weights, I don't run or do a lot of cardio as a huge part of my workout. I get dragged to Zumba every now and then and once I've wore this to a class I'll up date my review. However, I'm pretty small chested and I am not blessed..or cursed (which ever end your on) with a large chest I need to contain, so my review might not be worth much in that area.I will be purchasing more of these.02/02/16 UpdateWashed and hung dry, was so much easier to get over my head than the first time. Not near the tight squeeze it once was. Still loving this bra.