Oooh, the brand new Ryka aerobic shoes now are Ryka Rhythm's. Ryka Iseum are more cross trainers and are inferior to their aerobic shoes for Cathe training. I usually buy Ryka Stylus, but am going to get the new Rhythm's this week. I think they may have discontinued Stylus anyway.
Iseum does not have as much forefoot cushioning, and I noticed that they are much stiffer and take a long time to break in. They are comfy after that though...
For Cathe high impact though, aerobic shoes are the way to go!!!
Janice