"6. Maintain Wrist extension into and through the hitting zone.
To ensure the lag can be used to improve the hit."
I feel like this is vague and not necessarily true.
I personally believe that the correct way to use the hand is to initiate wrist abduction into a neutral wrist from the wrist lag position as you contact the ball. I don't understand the congruency of generating power to transfer "hips-shoulder-hand" and leaving your wrist extended through the hitting zone.
Please let me know if I'm wrong and if I'm perhaps just misunderstanding what is written. Thank you.
Also the capital W in wrist on step six seems to be a typo.
One of my 15 year old players, showing the use of the legs, the proper swing path, arm position, toss, balance and finish, this is an example of what all my players do. This young lady weighs about 85 lbs and serves over 100 mph. Skilled tennis is not about strength, it is about technique. You either learn it...or you don't. Those who don't learn ALL the elements of an Advanced Foundation, usually fail to reach their potential. (In all strokes and ultimately, abilities.)