I just got a stability ball and oh man I SUCK at staying on that stupid ball! And when I tried to the pikes I could not keep my legs locked, I kept bending my knees. I was trying so hard and was grunting and laughing at the same time. DH ran in the living room and thought maybe I was dying LOL! any tips to conquere this? All I can say it to get through this the abs must be screaming! }(