I can't do these either by the way - I can get one foot off the floor, but the other stays resolutely planted. I'm working on it - I'm too much into a good challenge to give up. I do feel it in the abs though - and I totally understand what you mean about needing longer arms - and I thought it was just because there is so much me (height wise - well, other wise, too, but I'm working on it!)
I have a question though. In the video, Brenda and I think Lorraine give a look to each other as if Cathe is absolutely nuts. I thought I saw Brenda, at least, having the same issue I have - she can get everything off the floor but that one foot. Am I merely wishful thinking and hoping that I'm not the only loser out there? LOL