Originally Posted by Ash_Smith
The point of a shadow swing (for me anyway) is to help the player develop the feeling of firing the muscles in the correct sequence (in other words to myelinate [or insulate] nerve fibres to speed up the impulse from brain to muscle). As the level of myelin builds up, the impulses can travel faster and so the ability to fire becomes more efficient and therefore can happen faster whilst maintaining control.
So, shadow swing slowly to develop the ability to fire faster (whilst maintaining control).
I agree. I always advise starting by basing the swing on a model (usually a touring pro) and doing the swing in slow motion. Once the player gets an understanding of the swing, then have them slowly speed it up.
My goal is to be able to swing with correct form at the pace best for the shot. Using video, I've found that the danger of swinging too hard when I'm grooving a technique is I tend to revert back to bad habits. That's why feedback, say from video, is very important. But eventually, I try to swing at a realistic rally ball pace with realistic footwork.
Some people advise swinging full speed with a racket without strings to actually up swing speed. I think there's something to this, but the reps should be kept low and you need to be warmed up to avoid injury. I don't know how important the change in balance of the racket is, but it is something to consider.