Justin Smith wrote:
it seems nice theory, but when getting thrown in reality, does one have time to put the arm behind the head? Is it even possible because centripetal force will throw your arms out?
Ok first centripetal force would be the force of tension holding your arms in. Your arms would fly out due to inertia… don't get me started.
I've never seen anyone put their arms behind their head in ukemi. Are there any videos on you tube or anything? I don't know what cradling the head looks like, but from the sound of it, I'd say you'd be more likely to break your arm, neck, elbow… than if you just tuck your head round your body and keep your arm out of the way.