Re: Aikido & Pilates
Basicallly, people develop patterns in the way they hold their body that result in muscles not being used in the optimal way. When you correct that you get the sensation of them "lengthening" - which is probably more accurately them just stretching out.
Look at yourself standing naturally in a mirror and notice your hands. If you see the back of your hands, odds are that you have an unhealthy pattern or two (or more). If you see the palms of your hands (be honest!) then I'd say odds are that your posture is much closer to optimal than the average person.
People who do Alexander Method talk about the sensation of your muscles lengthening and widening. This is pertenant to aikido in that I'd say many people in aikido have unhealthy body issues that really restrict/prevent reflexive movement.
I wouldn't say that yoga/pilates is the best thing to fix that specific problem I mentioned above. (I'd go find a St. John's method neuromuscular theropist for that one.) But, these problems cause weaknesses in core muscle areas and I have seen nothing better than the yoga/pilates combination to help. Core strength and flexibility are critical to aikido especially for developing fudoshin (unmoveable mind/mody).