Originally Posted by Bob B.

I haven't looked at the video but, if it's the one I think it is, I may have an explanation. Remember that the space suits are pressurized, thus the limbs of the suits naturally seek a straightened position. It takes effort to bend at, say, the knee. In the video I recall, the astronaut gave himself a little push with his hand and then straightened out his legs and quickly popped up to his feet. He could have been using the pressure inside the suit to give himself a little boost (like a coiled spring).