MF-HARPAwesome, was thinking it was more shoulders coz spinning the hips is a bit harder when you're clinging on a tube 5050 but will remember it next time I'm trying it. Now to analyse Will Wessons wizardry incessantly
I used to think it too, but after some trials while training martial arts I realized I was tottally wrong. Think about it this way, your hips are in the middle of your body, so rotating them rotates all your body instead of an independent part. For getting the same rotation by using only shoulders to rotate you should have to rotate more for making your feet be perfect for the landing. And, as it can sound strange, after you use your shoulders to help rotation get them as close as possible to your bldy to rotate faster (physics shit I don't fully understand, but it works).