[Updated January 2020 to reflect evolution of thought in the 11+ years since the post was originally published.]
In my first post -- Biomechanics: Ulnar Collateral Ligament -- I tried to focus on UCL injuries and how to prevent them. In one of my conclusions, I suggested delaying internal rotation until after arm extension. This post aims to analyze that concept in greater detail.
"Delayed internal rotation" is the term I use to describe the arm action in which internal rotation does not occur until after the elbow is mostly extended. In some instances, depending on the path of the elbow in space, this delay allows the triceps brachii to actively contribute to the throw. It remains to be seen whether this is beneficial to velocity or health when compared to intertial forearm acceleration which is believed to be more common.
In either case, given sufficient external rotation, delaying internal rotation allows elbow extension to occur in the plane established by the path of the humerus -- a sign of system efficiency, two segments working together -- and in the direction of the throw -- a sign of segment efficiency.
ARM ACTION - EFFICIENT SEQUENCING
As the humerus is accelerated, it generally moves in an arc. This arc establishes a plane of motion along with momentum (and therefore intertia) of the forearm and ball.
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. At this point, from a laid back forearm position, two actions continue the acceleration of the forearm: elbow extension and internal rotation. Sequencing matters.
When internal rotation occurs prior to elbow extension, whether intentional or not, the forearm moves from the laid back position into a more upright position, changing the plane in which elbow extension occurs.
As internal rotation pulls the forearm further out of a laid back position, the further toward the target the humerus must be for elbow extension to be efficient. While that increases segment efficiency, it decreases system efficiency as the forward velocity of the humerus is sacrificed to achieve this.
Additionally, elbow extension after internal rotation may be a factor for valgus extension overload syndrome which can lead to a number of pathologies in the elbow including ulnar collateral ligament tears.
When the elbow extends prior to internal rotation, the extension accelerates the forearm more directly toward the target and in concert with the forearm's momentum established by the path of the humerus. In this sequence, elbow extension can maximally contribute to pitch velocity and is a strong link in the kinetic chain.
As elbow extension decelerates, pronation, wrist flexion, and internal rotation work together to 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 4-frame image.
In the first frame, you can clearly see that external rotation has taken place with the forearm trailing the elbow.
In the second frame, Ryan has finished accelerating his elbow, and elbow extension has begun. His forearm is still trailing his elbow in a laid back position.
In the last two frames frames, Ryan's elbow extension is decelerating and nearly complete, internal rotation has begun, rotating his forearm toward the plate. As the pitch is released, pronation occurs, and internal rotation continues through the deceleration phase.
DR. MIKE MARSHALL AND ELBOW PATH
Dr. Marshall has something to say about elbow paths that have a large lateral component. From an email he sent me:
When, after 'traditional' baseball pitchers take the baseball laterally behind their body, they drive their pitching arm back to the pitching arm side of their body, they generate forces toward the pitching arm side of their body that 'slings' their pitching forearm laterally away from their body.
This can be fairly easy to see with the naked eye by looking for a lateral component to the elbow's path. For example, if a left-handed pitcher brings his arm toward third base (or a right-handed pitcher brings his arm toward first base), he must drive his elbow laterally to the other side of his body before he can accelerate toward the plate.
Much of this article assumes a traditional delivery in which the humerus moves in an arc as the shoulders rotate. Depending on exactly how the pitcher moves, this arc can be pronounced or nearly non-existent. A pronounced arc is the result of a greater lateral component in the arm path and creates more centripetal force on the forearm.
In order to control the slinging action, the brachialis contracts eccentrically. This not only opposes passive (inertial) elbow extension -- called "forearm flyout" -- it also prevents the triceps from maximally contracting.
Dr. Marshall believes those two effects to be inefficient and injurious because he believes:
- the triceps can generate elbow extension force that exceeds the centripetal force of a traditional delivery, and
- the lack of an effectual triceps contraction prevents the brachialis from properly decelerating elbow extension.
Frankly, I'm not sure either belief stands up to scrutiny, but I'm also far less qualified than Dr. Marshall in such matters. (It's also entirely possible that I've misunderstood or misstated his beliefs. You can investigate this for yourself at his website.)
IN A FEW PARAGRAPHS
A cursory analysis of primary arm action movements suggests that arm actions are generally more efficient when internal rotation is delayed until after arm extension. This means that less energy is wasted on movement that doesn't directly contribute to pitch velocity.
My conclusion: delayed internal rotation has positive performance implications.
This information, coupled with my previous conclusions regarding UCL health, leads me to believe that there are both performance and health benefits to delayed internal rotation.