Many are familar with the following video. Serve Doctor's Simplified Spring-loaded Serve Technique https://www.youtube.com/watch?v=Ixx-MCC7D88 This technique encourages the twisting of the core, separate the hips and shoulders to create the rotational energy. In a platform stance, at the trophy pose, I see federer's shoulder is almost inline with his feet and his hips. Does that mean there is no such twist force generated in the core? and all the rotational force is generated by the leg?