Not to sound like I am bragging or anything - but I think maybe you guys are trying too hard- when I first got the tapes on Jan 3, I couldn't do one inverted pike either. I showed my 16 year old daughter the tape and she did it the firs time! I know she is much younger than me, but she never works out!
I said that is it - I will get to do these if it kills me - I can do 40 of them at one time, but I will tell you I am winded and drenched when I get done and I do not come off the ball like Cathe does I do fall of the ball and say "Oh, my gosh!"
But I did find that I was weighting myself down, maybe because I was so tightened up - in other words trying too hard. Envision yourself (your butt and abs) as being light as feathers when you pull up. The ball barely moves - if you watch Cathe do it. I do mine with shoes with my toes pointed as I pull the ball forward, but when I peak up in a V my feet end up being flexed.
It took a few weeks to work up to 40 - but let me tell you I will not try to get to 50. I have been doing them for about 8 weeeks and I do not feel I can even progress to one more.
I feel the same way about the leg work on the Stability Ball - I have never thought, Oh, I will do another set of those, either.
Good Luck,
Cheryl