I'm becoming increasingly wary of slow motion practice. My reasoning is that it takes a different order of muscle contractions to execute a particular motion quickly than it does to execute it slowly, simply because muscular contraction is one force among many (gravity, key rebound, the elasticity of joints in the playing mechanism). Because of this, even if it were possible to execute a particular motion in slow motion, which may not be possible (the example Bernhard gave I believe was running, which cannot be done in slow motion), the slowed down motion would inevitably involve a different "script" of muscle contractions, which when sped up will likely be less than optimal. For this reason I believe that slow motion practice should be used very sparingly.
I agree with you and dinorsaurtales. That's why I said "Once you have figured out the correct movements at speed, you
can[/u] go back to slow practice if you want to, but it has to be a *slow-motion* version of the fast movements."
This whole issue would never arise if one wouldn't use the "start slowly, speed up gradually" approach. My main point was that, if one really wants to use that approach, it should be slow-motion, rather than using a different set of movements altogether. I wanted to point out that the "start slowly, speed up gradually" approach often leads to speed walls. I completely agree that slow-motion practice to overcome such speed walls won't work in many cases.
Having said that, both slow practice as well as slow-motion practice all have their place. In my own, personal experience, speed problems come from two sources:
1. Coordination: this essentially means the movements at speed haven't been properly worked out yet. This problem is solved by practicing at or above speed, although often, the "start slowly, speed up gradually" approach using slow-motion works too. This establishes primarily muscle memory.
2. Not knowing the music well enough: Once a note has been depressed one needs to know for sure what the next notes should be. This kind of memory can be obtained through slow-mode practicing (Bernhard advocates super-slow for this purpose) or mental practice. This is entirely different from muscle memory. For me this is the bigger issue when it comes to speed.
I think the trick is to know when a certain approach is useful and when not. They all have their place, and people respond to them differently. One needs to know about all of them.
As always, please understand that I am an amateur pianist and that what I post is only a result of my own personal experience.
We are all mere amateurs
Topic: Chopin op.10 no. 4