I guess I don't see how the the supination/pronation action relates to the grip being used or to the wrist position except possibly as a matter of degree of vertical velocity production - this action will cause upward motion of the racquet face with any combination in realistic near contact configurations.
Certainly hitting up through contact creates topspin - in the final analysis it boils down to what anatomical rotations best accomplish this task. The options are wrist radial deviation, forearm pronation (combined with upper arm internal rotation with straighter arm configurations), elbow flexion, shoulder flexion and/or abduction, or lifting of the entire upper body through action of the legs and/or waist.
From a mechanical perspective, some seem much more attractive than others based on geometric considerations and the associated joint rotation speed potential and range of available motion. Just a thought (or two).
Certainly hitting up through contact creates topspin - in the final analysis it boils down to what anatomical rotations best accomplish this task. The options are wrist radial deviation, forearm pronation (combined with upper arm internal rotation with straighter arm configurations), elbow flexion, shoulder flexion and/or abduction, or lifting of the entire upper body through action of the legs and/or waist.
From a mechanical perspective, some seem much more attractive than others based on geometric considerations and the associated joint rotation speed potential and range of available motion. Just a thought (or two).
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