Leon Aman wrote:
Do we always need to straighten our back while we are doing a technique?
Not at all - oops, sorry all pre-posters for contradicting
It is not necessary for doing good technique. If you have a hunchback or other problems, you can find ways to do all techniques in wonderful matter.
For all not too old and healthy aikidoka there are some reasons to straighten the back:
1) You can control your energy flow much better.
2) You can control your center and balance much better.
3) It looks much better.
4) You develop a "martial attitute"
There are probably more reasons and some are for different people more important than others.
And while some people do not need it at all to do stable, effective and goog looking techniques ("monkey style"), for some 80 to 90% of us it is the easiest way to get and stay there. That's why most sensei insinst in straight backs.
Just my 2 cts