That's the rub, isn't it. Outside of "do this-feel that" school of training (which I do not in any way criticize) there is almost no objective set of criteria to tell students what they are training for in their Aiki-taiso (they work to train this --done right); aikido waza (they work to train this- done right); weapons work ( they work to train this -- done right). To a practitioner who has "gotten it" in any degree at all, the "right" and "wrong" ways become progressively clearer to judge. But with little in the way of coherent objective explanation to aid the student in self-recognition of right or wrong manners of action, they are at sea, with no chart.
I do not think we are doomed to this though. My efforts at understanding aiki from a bio-mechanical perspective, have been fruitful, for me at least and for many of my students.
Erick, fruitful in what way? Do you mean you have been able to understand aiki from a biomechanics perspective?
What does that get you?
Speaking from personal experience I find the the former is favored at early stages of introduction by Yoskinkan, for example, later moving to combination with looser action. Iwama follows a similar way of progression, though in Saito's more programmatic and methodologically different way. ASU is a more eclectic bag with a eye for the expression of "principles" expressed in Saotome's views, in both tighter and more loose configuration of actions, in Aiki taiso, tai-jutsu and weapons work; Tohei's approach was fundamentally focused on the Aiki taiso, sometimes (it seems to me at least) to the near exclusion of studying application (at least in some quarters).
Aiki is the development of the body's ability to naturally -- and ultimately reflexively -- modulate its own rigidities and flexibilities of structure under dynamic conditions to form -- or to defeat the formation of -- these kinds of dynamics in connected structures (another person's body/weapon).
What was near to being lost was the "feel" of the Aiki in the body communicated in the inimitably intuitive Japanese mode of transmission. Some are finding western ways to emulate that -- and to good effect it seems. What we stand to gain in addition is a more Western and better developed objective understanding of the art, to make its transmission less dependent on correct enabling of physical intuitions across culturally-bound modes of transmission which tend -- at least IMO -- to work less well in our culture.
Personally, I cannot comprehend how anything like skill in martial arts, or even simply skill in movement or use of the body, can be attained without physical intuition. How does objective understanding help? It sounds as though you are suggesting that a student may be better able to manifest aiki if he watches some physics experiments on youtube.
To some extent, I think an objective understanding of a martial skill could aid in contriving a training regimen which is more effective, of fixes problems with, the attaining of skill by the practitioner. I think modern combatives research does this. Although modern combatives people certainly do not throw away traditional methods if they believe they work.
And at the end of the day, it never seems to matter if the student "understands" what they are doing. In fact, since it was a standard mode for koryu to absolutely WITHHOLD from a student knowledge that would lead to understanding of what they are doing until they achieved a certain level of physical intuition, I think you need to directly address that. How is it better for a student on the mat to have to mentally process everything before they do it? What happens when they think they understand something but are incorrect?