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« Texas Rangers Win-Curve Part I: Wins vs Attendance | Main | Biomechanics: Ulnar Collateral Ligament »

Delayed Internal Rotation: Performance Implications

[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.]

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.


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.

Velocity of an object moving in an arc.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.


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

Nolan Ryan's arm action - extending the arm from an externally rotated position.

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 homeplate.  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.


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:

What is critical in all arm actions is creating external rotation of the shoulder. Torso rotation (transverse and sagittal) creates the change in direction necessary to cause the forearm to lay back (external rotation of the throwing shoulder). The forearm lays back as a result of its inertia; i.e., a sudden change in direction (rotation of the upper torso) leaves the forearm behind.

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

Similarly, both agree that a laid back forearm positions the triceps to maximally accelerate the forearm toward home plate.

In his articles for The Hardball Times, Nyman makes no claim regarding the effect of the elbow's path on forearm acceleration, but 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.

In order to prevent this slinging action, the brachialis experiences an eccentric contraction.  This not only opposes passive arm extension - called "forearm flyout" - it also prevents active arm extension by the triceps.

In another point of contention, Nyman says that inertial forearm layback is necessary for maximizing pitch velocity.  Nyman's description of the inertial layback is identical to Dr. Marshall's description of late forearm turnover.

As discussed in my first article, late forearm turnover is the largest risk factor for UCL tears since the flexor-pronator mass does not strongly oppose the valgus torque that it creates.


The mechanics involved in over-hand throwing strongly indicate that the kinetic chain functions more efficiently 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.

Paul Nyman and Dr. Mike Marshall both agree on the principle reason behind delayed internal rotation - to utilize the triceps brachii as a key link in the kinetic chain - though Dr. Marshall does not agree with all of Nyman's reasoning.

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.

For more on Paul Nyman and Dr. Mike Marshall, check out my Online Reading list.

Reader Comments (2)

One thing I want to point out... the triceps do very little in terms of extending the elbow during pitching

when the arm moves in a circular path like you described, the degrees of freedom at the elbow joint allow it to extend on it's own, almost completely passively

it's like the merry-go-round ride with the swings that spin around... as the ride's angular velocity increases, the swings begin to move away from the axis of rotation

now imagine the ride had a huge angular acceleration (like the shoulder receives from a hor. add. torque) the swings would lag back (due to their own inertial properties) and then fly out almost completely horizontal

i think one of the first pitching studies (atwater, if my memory serves me) actually put a chemical agent on the triceps such that they were rendered completely inactive... when the pitchers threw, they still produced pretty good velocity... the slight decrease occurred because the triceps was used eccentrically to control the degree of elbow flexion during the cocking phase

a recent study decomposed torques into their components and the main extension torque was a motion-dependent torque (dependent upon the angular velocity and orientation)... I think it was by Hirashima... i'll get you a link if you want it

March 30, 2009 at 12:53 PM | Unregistered CommenterRick

You are referring to what Dr. Mike Marshall calls "pitching forearm flyout" (which I have shortened to "forearm flyout").

What you say is completely true for pitchers with severe horizontal rotational arcs, but the muscle that eccentrically contracts is the brachialis, not the triceps.

There are a number of arm actions that are half-way between Dr. Marshall's straight-line motion and the more traditional rotational/torque motion - typical short-armers fall into this category. One such pitcher is in my queue - Ryan Berry of Rice University.

There are a lot of things wrong with this article. As I state at the top, it is being re-written from the ground up.

Thank you for the comments.

March 30, 2009 at 1:41 PM | Registered CommenterTrip Somers

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