Do you think it's even possible to describe the body skill...the "how it's being done?" I mean, the way I see it, there's the left-brained-type (abstract modeling) of conceptualizing the series of events which constitute aiki waza and then there's the right-brained-type (spacial interaction) of sensing and performing the skills themselves. Thinking about how things are moving within the body (left-brained/physical mechanics description) serves as a guide for where to place the awareness so one can then sense and learn how to purposefully engage those skills in the space of reality.
The practical aspect that traditionally underlay everything (and is missing in most urbanized sedentary culture today) is in heavy manual labor of almost any suitably varied type. Morihei Ueshiba identified farming -- but that was his experience.
If you learn to deal efficiently at two types of tasks you will have the rudiments of whole- body skills and the "cerebellar" foundations that Chris (correctly) speaks about.
Repetitive center-driven reciprocal limb movements that emphasize sweeping or curling motions or twisting in or out motions.
Bearing, balancing and projecting bulky loads up and or out, and driving objects downward that require your body mass to accomplish.
Examples today that would encompass much of both of them would (still) be farming (cutting/reaping, shifting and tossing bales or sacks, pulling stumps of small trees chopping wood and hauling water, hand or tine-prong weeding (use screwlike motions)).
Construction framing is another good one that leaps to mind (driving heavy framing nails, shifting and lifting lumber and sheet goods, driving ground stakes, excavating, hand augering and screwing). That is all good physical foundation in body skills of the basic type at issue -- not mere general fitness.
What you build on it is another matter. The latter part is cerebral from that physical foundation and is built physically, but according to an intellectually sound plan.