Maybe I don't understand how scalable is meant, but this would seem to be
him talking of ways the serve is-
• Purposeful practise of internal rotation at the shoulder joint - this may be commenced at an early age, if an appropriate racket and ball are being used.
When shoulder internal rotation should be introduced into the teaching sequence is a question with no real answer. It can be taught relatively early in the learning process, however, it certainly will not achieve its ultimate goal of dramatically increasing racket speed until the factors discussed in point 7, as well as muscle strength have been appropriately developed.
probably not the correct link or correct paper to see the proper ref to the topic though
Pro Supex Big Ace