[To introduce: this was the offshoot of a discussion on musubi and speed that arose in the ground fighting thread. I thought it warrranted its own space for further development.]
Michael Fooks wrote:
My concern is that without practicing at full speed you not be able to maintain musubi when attaceked at full speed. The [dicussion] is starting to indicate that you actually advocate starting slow and building up to full speed? If so we're in agreement.
I do recommend understanding how things change at different speed once people are comfortable, but not in the way it seems that you mean.
For most techniques at full speed, a little touch of true musubi (even just with atemi) is all that is required to effect a throw, drop or transition the attack into osae waza. It really becomes more ukemi-limited for uke's safety than for nage's technique. Someone said that the mistakes in aikido are more dangerous than the techniques. This is one illustration of that. It takes time also for uke to be comfortable in adapting his musubi in the ukemi as well, which can be progressively unpredictable the faster that one goes, and not just harder and faster. There is a fundamental physical reason for this.
Going fast does not necessarily have the effect intended -- if what you are driving at is acheiving close and predictable correspondence between rhythm of attack and rhythm of selected technique at progressively higher speed, just harder and faster. Going fast inherently breaks into different rhythm from going slow (one of the reasons why kaitennage feels different slower, and why "speed" is not exactly meant the same way by different people).
That is why people walk at differnt rhythm than they jog, and jog and different rhythm than they run. It is no just faster, Notice that we have only three normal gaits for getting around at different speeds. There are a couple of others but they are more specialized and are not about moving over large distances efficently.
Chaotic systems theory illustrates this rhythm altering by increasing flow rate in a dripping faucet -- first you get one stable rhythm, then two different stable rhythms, then three, and if you dial up the faucet one more time --- at that point the systems becomes chaotic and indeterminate and any rhythm or no rhythm exists in the system.
By increasing speed of attack in the same way, tactical sequences very shortly go out the window, and only musubi will keep up. Speed also has less advantage when seen from the standpoint of inherently altering rhythm. This creates suki that uke did not intend when he went in full tilt, and which do not even exist if he were moving with somewhat greater deliberation. He will fail to recognize it unless it is shown to him at a training pace (which will seem artificial at that pace, even though it is not.)
Another reason to focus on following the musubi rather attempting to train for tactical sequences in advance and then faster (other than for training to abandon them). Going faster changes more than just energy.