Naturally, the goal is that this interaction will build over time toward fluency in the face of full speed and full power. In the meantime, however, there is the phenomenon whereby the attacker will continuously adjust his slow-motion punch, for instance, following the defender's movement quite unnaturally so as to land the strike. Here, I often find myself cautioning the the students:
No guided missile attacks!!!
... but I have come to reconsider whether my advice is actually counter-productive.
Where Does it Come From?
Consider: Following the defender does in fact represent the attacker's pure intent to find his target. After all, no one instructed the students to chase their opponents with a punches, for instance, so we really have no choice to consider this movement somehow natural and pure. This purity of intention is precisely the root of the often discussed "fully committed attack" and is something we wish to cultivate at least through the intermediate stages of practice, giving the defender the opportunity to practice the principles and techniques of handling this energy.
As practice moves through intermediate stages into the advanced practice, the defender must learn to deal with the less-than-fully-committed attack (such as feints and combination attacks) and recovery from failed techniques (including changing techniques). Here, the defender must be sensitive to the attacker's intention and energy as well as to changing conditions in order to practice operating "freely." Also at the higher levels, the attacker should learn not to follow his physical attack with his mind. As noted in an earlier post, the archer need not "follow" his arrow downrange to see if it lands; rather, he should ready his next arrow or moving from the area. Launching even a powerful attack need not be more than an impulse on the attacker's part, allowing him to observe and to make adjustments from a centered state. At this stage, the attacker should become sensitive to the defender's attempts to manipulate him and should learn to take advantage of them (such as with countering techniques).
The "guided missile" is perhaps the simplest and most explicit example we have of the principle of "leading ki." If, for instance, we see an attacker reaching to grab your shoulder, and if the attacker is actually intent upon grabbing your shoulder, your pivoting your body back away from the grasp so that your shoulder stays just ahead of the attacker's grasp will likely draw the attacker off balance into the circular motion of your pivot. There is the "guided missile" in a more realistic attack, and it is precisely the affect we are practicing to create. We would not correct the beginning or intermediate student for pursuing the shoulder, would we?
Naturally, there is a balance to be struck between practice and realism. Consider that if the defender pivots too quickly, placing his shoulder obviously out of reach, the attacker would be hard pressed to follow; instead, he may realistically select a different target and reengage---no guided missile occurs. Here, we may laugh if the attacker does continue to pursue that particular shoulder as the defender pivots around and around and around, but for training beginners, we can discern the value of such apparent silliness.
So, what about the munetsuki "lunge punch" or shomenuchi "downward strike" that tracks the opponent? Well, in fact they do, just not as dramatically as when performed in slow motion. The strikes are not essentially different than the grabbing attacks except in the amount of power present and perhaps in the intent (perhaps to harm rather than to control, for example). As the speed and power develop, the attacker will simply not be so able to follow so directly.
It is an interesting phenomenon that students and teachers alike should consider.