Originally Posted by Cheetah
I'm not for nor against MTM.
That's an inside-out fh. Roger's i/o fh's have sidespin.
That's only 1 stroke. Surely Roger doesn't put the same spin on every shot. Maybe that shot had sidespin. Maybe it didn't. We don't know because that's from the APS vid and we don't have the actual vid of the shot correct? Or do we? Do we know if Roger hit the inside of the ball? (which would create sidespin)
This is my old post from famous deleted MTM thread.
Let’s assume a player rotates straight arm around shoulder joint with locked bend back wrist in horizontal plane and without arm pronation, see please picture below.
The angle (ϕ) between long axis of the racquet and axis of the arm is 45°.
The arm rotation creates around impact linear racquet speed Vshoulder. Accordingly to the linear algebra, every vector of the racquet velocity Vshoulder can be decomposed as a sum of two orthogonal (perpendicular to each other) components (vectors). The normal component VshouldNorm is the perpendicular to the strings and the tangential component VshoulTang is the parallel to them.
The normal component (VshouldNorm) mostly defines ball’s direction and ball’s translational speed. Tangential component (VshoulTang) creates mostly clockwise sidespin.
If ϕ=0 there will be no sidespin at all.
Thus, the larger the angle ϕ, so there will be more sidespin. Apparently that sidespin has nothing to do with pulling across or whatever the name is, it is defined by position of the wrist relative to the arm/forearm.
On winner attempts, that are usually flatter, we have to decrease ϕ angle to minimize useless sidespin and thus increase translational ball speed.
I think in next picture Federer hits hard FH with some clockwise sidespin.