[Last edited on: Tuesday, January 27, 2009 at 7:55 PM; I freely admit that this article isn't very good, and instead is actually pretty worthless. Read it if you want, but I advise that you take none of it as gospel or science or expert advice. I am re-writing it from the ground up, but I am not sure when it will be published.]

[Update: Tuesday, March 31, 2015 -- This is a bad article with many factual inaccuracies. I may never rewrite it. I may actually delete it at some point, but I believe there is some value in its inquisitive, explorative nature.]

In the previous article Biomechanics: Ulnar Collateral Ligament, the discussion centered on what causes UCL tearing and how to prevent it.  In one of my conclusions, I suggested the delay internal rotation until after arm extension.  Now, I will discuss this concept in greater detail.

Delayed internal rotation is the term I use to describe arm action in which internal rotation does not occur until after the arm extends.  Done properly, this arm action allows the triceps brachii to maximally accelerate the forearm directly toward the target.

Internal rotation changes the orientation of the humerus and the direction in which the forearm moves during arm extension, so sequencing is important for efficient energy transfer through the kinetic chain.

ARM ACTION - THE KINETIC CHAIN

The kinetic chain starts at the ground, moves up through the body, and ends in the finger tips.  Since the focus here is on arm acceleration, this analysis of the chain will start at the shoulder with the upper arm in an externally rotated position.

From the shoulder, a series of arm movements is responsible for completing the chain.  As the humerus is accelerated, it establishes a plane of motion.

Within this plane, the humerus moves in an arc.  The distal end of the humerus (near the elbow) reaches peak forward velocity shortly after the humerus is perpendicular to the line between second base and home plate.

Beyond this moment, the velocity of the humerus is directed somewhere other than the target.  If the humerus moves past perpendicular, the rest of the arm and the ball move with it.

The kinetic chain "breaks" when the forearm and wrist compensate to put the ball's path back in line with the target.  To maintain the integrity of the kinetic chain, all parts of the arm must apply force in the same direction.

Arm extension and internal rotation are motions that also create arcs, so the same rules apply.

When internal rotation occurs before arm extension, whether the internal rotation is intended or unintended, the forearm moves from the laid back position into a more upright position and the medial epicondyle faces the target.

From this position, the arc created by arm extension is in a plane that is perpendicular to the the line between second base and home plate.  Even though the arm extends rapidly, the contribution to pitch velocity is minimal.

This is a break in the kinetic chain that also negatively affects the potential velocity contribution of pronation.

Arm extension after this point may result in valgus extension overload syndrome which can lead to a number of pathophysiological conditions that may include ulnar collateral ligament tears.

[Note: Dr. Mike Marshall believes that valgus extension overload syndrome does not exist. I tend to believe that it does exist but that it may be irrelevant with regard to pitching. More to come on this.]

When the arm extends before internal rotation, the triceps can accelerate the forearm directly toward home plate in the same direction in which the humerus was accelerated.  In this sequence, the triceps can maximally contribute to pitch velocity and is a strong link in the kinetic chain.

After the arm extends, pronation, wrist flexion, and internal rotation can continue the kinetic chain and powerfully finish the pitch directly toward home plate.

A HALL OF FAME EXAMPLE

Take a look at Nolan Ryan's arm action in the following image.

In the first frame, you can clearly see that external rotation has taken place.  The forearm must trail the elbow for the triceps to be able to accelerate the forearm toward home plate.  External rotation positions the arm for this, but the method used to create this external rotation is as important to UCL health as the external rotation itself is to pitch velocity (see the previous article).

In frame 2, Ryan has nearly finished accelerating his elbow, and arm extension has begun.  You can see that his forearm still trails his elbow in a laid back position allowing arm extension to occur in the same direction as his humerus.

In frames 3 and 4, Ryan's arm approaches full extension, internal rotation begins, and his forearm starts to turn forward toward the plate.  As he releases the pitch, pronation occurs, and internal rotation continues through the deceleration phase.

PAUL NYMAN AND DR. MIKE MARSHALL AGREE... SORT OF

They don't really agree on this issue, but they have some similar things to say.  In an article written for The Hardball Times in May 2008, Paul Nyman said the following:

Dr. Marshall agrees that the forerarm should lay back, specifically that the ball should be kept at full forearm length horizontally behind