GSP is flexible. You do not know if that video was truly to show his inflexibility or him trying to stretch out a cramp or balled up injury. I have seen him do full force Taekwando roundhouse headkicks. If he says he is inflexible, he probably means, he is not as flexible as an Olympic gymnast and it is bothering him. This does not mean he is gonna win or lose against shields, just an observation.