I’d love to see this research. Based on my experience as a professional tennis player and coach for over thirty years, these methods hinder people at every level. Breaking down each part of a movement and then verbally repeating some instruction completely takes the student out of their focus on the present.
“The Inner Game,” by Tim Gallwey was the biggest breakthrough in the history of peak performance science. Pete Carroll, coach of the Seahawks has used the book since his days at USC when they brought in an Inner Game trainer. The Yankees have also used the same trainer.
I find that internal cueing can only be done as part of a pre-performance visualization and practice swinging. You’re not saying the words to yourself in so much as recreating the muscle sensations you have experienced during previous practice. Usually, I will ask a student to close their eyes and swing the racket so that it feels good to them, based on whatever level of experience the have. Once I get them to recognize how a particular action feels — say, for example, a flat racket face versus one that is open or closed — everything becomes a question of guided awareness.
Instead of saying to them and having them repeat to themselves “keep your racket face flat,” I ask them to be aware of how their racket face feels as they make contact with the ball. There is no stress, or self judgment, just a detached focus on the now.
In a short time, they will absorb the muscle sensations that correspond to the angle of the racket face. In addition, without saying a word about the results, the body will make a connection between balls that sail upwards (open face), those that go fairly straight (flat face) and those that go down into the ground (closed face). Since most people like the idea of being able to hit the ball over the net and into the court, they figure out immediately which muscle sensation yields the desired result.
You would be amazed at how quickly even a beginner can develop consistent racket control once they are learn the principles of body awareness and then trust their body to do what feels good.