Re: Suwari Waza
I have never seen injuries as a result yet have seen how easily damage can be done to the knees by those who don't do it properly.
There are no doubt reasons why and how it can damage the knees due mainly to not being used to using them in such a way and people like carpet fitters are a good example of those who after a while get knee trouble.
However, we are talking Aikido and from my view it's learning how to do it properly that is the main protection far and above all other 'theories'.
Firstly I would say it is well worth doing and much is learned from so doing which otherwise would be missed. Second would be a matter of when? The simple answer is when the person is ready and not before.
Thirdly I would say approach is the key. Approach meaning prior things to be in place and practiced first in order to get full benefit and freedom of movement and thus no damaging effect on the knees.
Just doing kokyudosa would be pre sawariwaza as an example and is a good way of getting the knees and feet used to such positioning as well as just sitting seiza for small periods and extending them.
Then in order to even attempt suwariwaza I personally would have to see the student comfortably doing taisabakI 180% back and forth continuously at ease.....from centre., Until a person can do this...from centre....then they will damge their knees if made to do lots of suwariwaza. So basically centre protects the knees is my motto.