I think you just have to be careful to not go too hard so you don't injure yourself, I think that's why people always seem to do it on an exercise bike - so the range of motion is limited and controlled. There was a news reader who did it on a rowing machine who yanked too hard, tore the artery in his neck and had a stroke, but that's a bit retarded to be honest, as long as your not silly about it and don't have that retard strength where you can basically snap your own neck from flipping out too hard when you're exercising you should be okay.