the term "internal rotation" as it applies to underhand pitching
is about delaying the inward turning of the upper arm (humerus) and then the lower arm (radius/ulna).
To make a windmill motion to pitch a ball, "internal rotation" (of both upper and lower arm) has to happen.
You can't really make an arm circle without it happening.
The important consideration is when it happens.
The "palm up" position we strive for at the 10:00-9:00 position in the arm circle,
has everything to to with delaying inward rotation of the humerus,
and not much at all to do with the radius/ulna.
(internally rotating the Radius/Ulna while holding an externally rotated Humerus, behind you at 9:00 is probably possible, but pretty awkward...)
Once the ball passes 10:00-9:00 everything happens pretty quickly,
but the internal rotation of the upper arm (humerus) generally very slightly precedes
the internal rotation of the forearm (radius/ulna) which occurs last in the kinetic chain
at the very bottom of the arm circle and just before release of the ball.
All of that "stored energy" of delaying internal rotation of both upper and lower arm,
is what contributes to greater speed AND spin.
The "Forearm Fire" guy was hyper-fixed upon the lower arm,
but that is only one part of the kinetic chain we are interested in.
is about delaying the inward turning of the upper arm (humerus) and then the lower arm (radius/ulna).
To make a windmill motion to pitch a ball, "internal rotation" (of both upper and lower arm) has to happen.
You can't really make an arm circle without it happening.
The important consideration is when it happens.
The "palm up" position we strive for at the 10:00-9:00 position in the arm circle,
has everything to to with delaying inward rotation of the humerus,
and not much at all to do with the radius/ulna.
(internally rotating the Radius/Ulna while holding an externally rotated Humerus, behind you at 9:00 is probably possible, but pretty awkward...)
Once the ball passes 10:00-9:00 everything happens pretty quickly,
but the internal rotation of the upper arm (humerus) generally very slightly precedes
the internal rotation of the forearm (radius/ulna) which occurs last in the kinetic chain
at the very bottom of the arm circle and just before release of the ball.
All of that "stored energy" of delaying internal rotation of both upper and lower arm,
is what contributes to greater speed AND spin.
The "Forearm Fire" guy was hyper-fixed upon the lower arm,
but that is only one part of the kinetic chain we are interested in.
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