Re: Adapted Training
I like the spirit of Janet's post. I think aikido is a great art for a variety of reasons, and it can embrace a range of participation. Ultimately, adapting your personal needs to the training environment will reflect on your personal progress, but that is another thread.
I have had the opportunity to work out with a number of people with a variety of needs. As I tell my 5-year old when we fish, "there is one place where the fish will never be... out of the water." I think encouraging people to understand that while they may never reach a level of stewardship or expertise, neither proficiency is required to enjoy training. Training is required to enjoy training.
As a larger statement, I think the only real requirement for aikido training is the ability to express and receive energy. In theory, I can do both things from any point on my body if I have aiki. The method is which you provide energy for me to manage should be irrelevant, contingent upon my skill. The manner in which I express how to use that energy is irrelevant, again contingent upon my ability.
The farther you move away from that larger relationship, the closer you move to jujutsu because the exchange of energy becomes more occlusive, requiring greater collaboration about what is happening. The nature of adaptive training is going to suggest a reduction in the athletic requirement that often accompanies jujutsu. Jujutsu is the form in which we are generally intended to express aiki; that by no means should be seen as the exclusive means of expressing aiki.
You can absolutely express aiki from any point of contact. There are high-level people doing parlor trick seminars right now, trying to get across this very point and trying to bring is into our daily training, not just something we see at big seminars. It does require managing your expectations about what is happening, though.
I think sometimes we are conflict with ourselves. The art is professed to be an exploration of aiki, yet the teaching methodology often pits a pseudo-adversarial partner against your intention to "explore." Eventually, it should not matter. Initially, its counter-productive. Unless you are working on the jujutsu end of things, in which case you are training with the intention of off-balancing your partner, not just providing a vector of energy to explore. I think either extreme is undesirable, but the flow within the bell curve has elasticity to accommodate variety.
Just to make things more complicated, (and to Janet's point), the amount of pressure is also, technically, not relevant. Asking your partner to apply more pressure than they are capable of applying is just as abusive as applying more pressure than your partner can receive. Baby bear energy, just right.