I don't think any of those directions are dangerous specifically.
Two things make falls dangerous, the amount of vertical (as opposed to horizontal) in a fall, and stopping the flow of a throw abruptly before it's completion.
Horizontal falls lend themselves to pretty easy breakfalls, however vertical falls (i.e. upside-down, either shoulder first or head first) are very dangerous and more difficult to control.
I was living with my Uncle, and he only had one spare key that he kept hidden in the garage. One day I needed to come home early, so I was just going to hop over the fence and go into the garage. I pulled myself up to the top the fence (6 feet), with both hands on the top board I swung my leg up and placed my foot next to my hands on the top board, leaned over and prepared to kick off the fence and jump into the yard. Well the inside boards of the fence were all made of particle board to save money (chunks of wood laminated together -- not solid natural wood boards) and it snapped with all my weight on it -- and in an instant I slammed head first towards the ground (all concrete around his pool).
I had one breath to do "something", so I wrenched my upper body to land more on my shoulder than my head and stuck out my arm just before I hit.
My hand and arm absorbed nothing, they crumpled like tin foil, I hit shoulder first instead of head first, but my neck whipped and my head stuck the pavement anyway (albeit not very hard). The rest of my body went sort of backwards and fell into a crumpled mass of Bruce. I was so shocked by the whole thing that I just lay there looking at the pretty blue water for a while.
So because the fall came unexpected, I just couldn't react fast enough to fall better (perhaps if I had a little more time my arm could have been extended and more circular before I struck).
The other real danger I have seen cause the most damage in Aikido, is when nage does a strong flowing throw, but then stops his/her motion short of the proper completion (either by accident because they hesitate, or on purpose because they want to injure someone). Again when uke is in the motion, then suddenly has to "save themselves" they can't do it fast enough and it usually results in an awkward and painful fall (many times an injury).
Last edited by BKimpel : 09-28-2003 at 11:11 AM.