...So why are you training the slow kick with different technique than the fast kick? The slow kick should follow EXACTLY the same route as the fast kick. When you can perform the technique slowly, you have more strength, more ability to incorporate the mass and rotation/thrust of the entire body into the fast kick, instead of relying entirely on the whip and speed of the kick, utilizing primarily only the mass of the kicking leg. Your slow kick should look as though you filmed the fast kick at 1000fps and watched it in slo-mo. I agree, if the novice is performing the slow and fast kick as different motions, they are not helping themselves.
I would suggest that if the student thinks that the slow kick you describe is the same as the fast kick you describe, they have a very poor understanding of the mechanics of the fast kick. Some dedication to learning the precise motions of the fast technique, at very slow speeds, might be a valuable training boon to such a student.
I notice a direct correlation between where I can kick with good technique, and where my technique begins to suffer; and where I can kick slowly. Take, for example, the round kick. Moving slow, I can pivot my foot, twist the torso and hips in the direction of the kick, arc the leg through the chamber and towards its extension, and as it extends, move my upper body in the opposite direction, forcing the leg into a short segment of added speed and full body commitment, maintaining good technique and foot position. That is all slow, and I can do it to about a solar-plexus level. When I perform the same kick at speed, the EXACT same motions are performed, and I can land a very powerful round kick, at that level.
When I kick high, I can do a decent kick, that looks every bit as good. However, as soon as I rely on momentum to force my leg/core past where it has the musculature to go without momentum, the power takes an instant dive. Suddenly, I have speed, but far less mass/commitment. The same goes for any of my other kicks as well.
I have also noticed, as I'm sure you have, the difference between many practitioners' in-the-air kicks, and their against-a-target kicks. Front thrusting kicks may be the clearest example. Students do the kicks in the air, and they automatically fall back on the fast, flashy snap kicks, that rely on momentum of leg lift to propel the kick into the target. Hold a target in front of them, and the kick changes, automatically, into a kick that compresses to the chest and propels outwards, relying on core strength and powerful leg extension. It amazes me how consistently students will make this switch automatically, and not even know that they do so.
Now, in my style, the first kick is NOT what we are looking for in a thrust kick, but the second one is. The first is easy to do fast, but not very powerful. The second requires a great deal of strength and control, but has greater body-mass involvement and thus penetrating power. By training slow, I have seen students air-kicks begin to more closely resemble their target-kicks, even over the course of a single class. Yes, it takes more time to practice 25 slow kicks than to fire off 100 full speed kicks, but the improvement I have seen in myself and others seems to justify this.
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Finally, of course fast and slow training are different. The muscle groups needed are in many cases even different, (cue introduction of elastic resistance bands to utilize correct muscle groups!!!) especially when the kicks are performed differently, as in the case you cite. However, the musculature needed for a slow kick is ALSO needed for the fast kick, but is often bypassed when relying on momentum, rather than muscular control, to propel the kick through the correct trajectory. By training slow kicks, you can train details of body mechanics which are difficult to enact at speed, and you build strength to assist the kick, instead of relying on momentum.
I have seen in students, immediate improvement in technique after practicing slow. I have felt in myself, immediate and long term improvement in detail of the kick, specifically focused on training slowly. Perhaps, with the mechanics of kicking differing from style to style, slow kicks are more beneficial in some systems than in others, but in mine, they have been quite literally proven to improve kicking technique.
It's a tricky subject to address in text, specifically because it DOES address such fine elements of detail, timing, and nuance, but for myself, I value slow kicks immensely.
Out of curiosity, how do you drill and teach the finer details of kicking if you don't practice and/or demonstrate slowly? At speed, it is, for most students I have seen, much more difficult to incorporate specifics of motion.
