I doubt that anyone has noticed that I play possibly the fastest vibrato of any other thereminist. Not due to any particular skill, but rather simple physics.
The open hand is much like the spinning ice skater with arms extended - more momentum, less speed, my hand is cupped, much like the spinning ice skater with arms drawn inward - less momentum, more speed.
Extended fingers and open hands limit the speed of your vibrato - just physics.
Not enough for me, though, so I had started making a fist to increase the vibrato speed even more, but only slightly faster. the problem is that the nervous system goes only so fast, so I met with another barrier, the Vibrato Barrier.
Solution is very simple, as one makes a fist with the pitch hand, tighten all the muscles in the pitch arm and wrist until the muscles go into self oscillation - a trembling and shivering effect. Since the range of motion is very limited this technique is most effective on the higher octane ranges. As one goes lower in pitch the effect lessens to a subtle growl added to the lower notes and for bass it is pointless.
My favorite cliche with this technique is to start with a very slow vibrato and ramp it up to ultra fast vibrato.
Like all vibrato, this technique should be used sparingly. No pain issues or joint issues since little actual motion is involved. No carpal tunnel issues hopefully.
This technique should be attempted only by the best professional precision thereminsts who are capable of playing with or without regular vibrato.
Like Charlie Draper.