[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.

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.

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.

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 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.

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:

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.

IN A FEW PARAGRAPHS

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.

[Last edited on Tuesday, January 14, 2009 at 2:47 AM; the "In the Delivery" section is being re-written from the ground up. It is not very clear, nor is it entirely accurate at this time. The re-write will fix this; however, I do not know when I will have it ready.]

Throwing a baseball is not nearly as simple as it seems at first glance. Different parts of the arm and body accelerate and decelerate at different times and different speeds. Analysis of the order and timing of these movements can help evaluate a pitcher's injury risk and isolate areas of inefficiency. When it comes to preventing injury, two areas are focused on above all others - the elbow and the shoulder.

Initial pitch velocity is created by the legs and core. As the arm accelerates, muscles of the upper body and arm add to this, sending a large amount of energy through the elbow. An inefficient transfer of this energy can lead to injury in soft tissue and bony tissue alike.

The most well known of these injuries is a tear of the elbow's ulnar collateral ligament (UCL).

ANATOMY

3 bands of the ulnar collateral ligament: anterior (red), posterior (blue), transverse (yellow).Significant tearing of the UCL is often the result of an accumulation of micro-tears caused by repetitive near-limit stress, but it can also result from a single catastrophic event - almost never one "bad" pitch.

Valgus force, which is a prime component of valgus extension overload syndrome, is responsible for the tensile stress that causes these tears. In the elbow, valgus force is measured by its rotational translation valgus torque. This force "pushes" the forearm and hand laterally.

[Note: Dr. Mike Marshall believes that valgus extension overload syndrome does not exist. I tend to believe that it does exist but that it is potentially irrelevant with regard to pitching. There is more to come on this topic.]

The UCL connects the medial epicondyle of the humerus to the coronoid process and olecranon of the ulna, and valgus torque increases the separation between these bony structures. Increased tensile stress on the soft medial tissues of the elbow is the result of these bony structures being pulled apart. This tensile stress, caused by valgus force, is appropriately called valgus stress.

The flexor-pronator mass also anchors the foreram to the medial epicondyle. This collection of muscles is comprised of the pronator teres and the forearm flexors. Contraction of the pronator teres causes pronation - medial rotation of the forearm. Contraction of the forearm flexors creates wrist and finger flexion.

When these muscles contract, varus torque is generated. The varus torque contribution from these contractions varies from pitcher to pitcher and even from arm to arm based on the strength of the muscle group and the magnitude of the contractions. A strong enough contraction will hold the ulna firmly against the humerus effectively reducing valgus stress in the UCL.

SCIENTIFIC STUDIES

Between 30° and 120° of elbow flexion, the UCL is the primary stabilizer against valgus force.¹ Outside of this range, bony structures and other soft tissues take larger roles in stabilization.

Morrey and An showed that, at 90° of flexion, up to 55% of the stabilizing force is contributed by the UCL.⁵

A study by Fleisig, Andrews et al. estimated the average peak valgus torque to be 64 Nm (Newton-meters), with a normal range between 52 and 76 Nm.⁴ Building from the Morrey and An study, 55% of this is roughly 35 Nm, with a normal range between 28 and 42 Nm in UCL stress.

This number is in line with the study by Dillman et al. that showed an average failure load of 32 Nm.³ This indicates that pitching frequently results in stress that is far in excess of the observed failure load of the UCL.

These widely cited studies, though, were performed on cadavers and do not measure the varus torque contribution of contracted flexor-pronator muscles. If a pitcher's arm actually relied primarily on the UCL for valgus stabilization, UCL tears would be routine, expected, and basically unavoidable.

In another cadaveric study, Park and Ahmad measured the valgus correction of individual muscles in the flexor-pronator mass. The muscles were electrically stimulated, and their valgus correction angles were measured. Park and Ahmad concluded that the flexor carpi ulnaris and the flexor digitorum superficialis were the primary and secondary stabilizers, respectively.

Somewhat surprisingly, their tests also showed the pronator teres to provide the least dynamic stability.⁶ This may or may not be true for throwing athletes since they typically have stronger pronator teres muscles than an 'average' cadaver.

Arm wrestling is an example of a non-pitching activity that creates extreme valgus force. Arms are typically positioned at approximately 90° of elbow flexion, and the force is applied in far greater amounts over much longer periods of time than in pitching. Arm wrestlers have immensely strong forearm flexors which prevent most of this force from stressing the UCL. Arm wrestling seems to result in far more injuries to bony structures (avulsion fractures of the medial epicondyle) than to soft tissues (UCL tears), but I found no studies that provide evidence of this.

IN THE DELIVERY

Valgus force is created by the inertia that opposes medial acceleration of the forearm which occurs after external rotation, during internal rotation, and to a lesser extent during horizontal shoulder adduction.

Physics tells us that valgus torque is greatest when the elbow is flexed to 90° (explanation in the following section). In the Morrey and An study, it was shown that the UCL handles its largest relative valgus load when the elbow is flexed to 90°. Combined, these two facts illustrate that valgus stress in the UCL is greatest when the elbow is flexed to 90°.

Rangers prospect Tommy Hunter at approximately 90° of elbow flexion (Photo Source: Scott Lucas)In the 'traditional' delivery, the pitching elbow is usually flexed near 90° from the late cocking phase through the early part of the acceleration phase. In fact, in a 1992 study by Conway, Jobe et al., 85% of their subjects experienced their greatest pain during the acceleration phase.²

The early part of the 'traditional' cocking phase involves active external rotation of the upper arm. When the active phase ends, external rotation continues in an inertial phase. The valgus torque of the inertial phase is only loosely opposed by the flexor-pronator mass because its muscles do not fully contract until the arm starts to accelerate the ball. Wrist extension during this phase increases valgus torque and prevents the forearm flexors from contracting effectively.

The inertial phase of 'traditional' cocking turns the forearm over. Because the forearm turns over after the body has begun to accelerate the arm, Dr. Mike Marshall calls this "late forearm turnover."

This inertia is increased by delayed forearm turnover - when "late forearm turnover" becomes "later" - which causes more forceful active external rotation and creates an opposition of forces with the elbow starting to move forward and the forearm trying to lay back.

Pitchers who pick up the ball with their elbows - hand below the elbow, as in Chris O'Leary's Inverted W, Inverted V, and Inverted L positions - are great examples of delayed forearm turnover. At foot plant, when the body begins to really drive the shoulder, these pitchers are still picking up the ball.

By delaying pick up, a pitcher must externally rotate his arm more aggressively because he is giving himself less time in which to properly position his arm for the throw. This delay also guarantees that the upper arm is already being accelerated by the body as the forearm lays back.

Right before the forearm muscles contract for acceleration, the upper arm begins to accelerate relative to the torso. In many cases, but not all, the pectoralis major contracts to start this acceleration. When it contracts, it horizontally adducts the humerus and causes incidental internal rotation. This internal rotation exaggerates the inertial effect of external rotation on the UCL in the instant right before the flexor-pronator mass contracts.

This event causes a "bounce" in the forearm that is often called "reverse forearm bounce" - another term coined by Dr. Mike Marshall. When the pectoralis major does not contract, internal rotation is delayed and "reverse forearm bounce" does not occur.

REDUCING VALGUS STRESS IN THE UCL

To a large extent, pitchers reduce UCL tension with a varus torque contribution from the flexor-pronator mass. Stronger contractions of this muscle group result in larger varus torque contributions. As the varus torque contribution of this muscle group increases, valgus stress in the UCL decreases.

Additionally, a strong pronator teres can powerfully pronate the forearm through pitch release. Doing so will help prevent hyper-extension and, as discussed above, reduce valgus stress. Powerful pronation also has positive performance implications for pitch velocity and ball rotation (pitch spin).

My conclusion: functional strengthening and conditioning of the flexor-pronator mass is beneficial to the health of the ulnar collateral ligament.

The best way to reduce UCL injury risk, though, is to minimize the valgus torque caused by external rotation and internal rotation of the upper arm. A little bit of physics will help explain how to do this.

According to mechanical physics, torque (t) is equal to force (F) multiplied by the distance (r) from the axis of rotation at which the force is applied, t = F*r. To reduce torque, F or r must be reduced. Since the mass being accelerated is constant (forearm, hand, and ball), the only way to reduce F is to decrease acceleration. This is clearly counterproductive to achieving maximum pitch velocity.

To decrease torque, then, r must be lowered. In other words, the mass being accelerated must be moved closer to the axis of rotation. In this case, the axis is a line extending through the length of the humerus.

With the elbow flexed to 90°, the mass can be moved no further from the axis, so r is greatest with the elbow flexed to 90°. With the arm fully extended, the mass can be moved no closer to the axis, so r is least with the arm fully extended. It then follows that the torque experienced during external rotation and internal rotation is greatest with the elbow flexed at 90° and is least with the arm fully extended. Plainly put, the valgus torque caused by external rotation or internal rotation is at a minimum when the arm is at full extension.

Additionally, at less than 20° of elbow flexion, the bony structures of the elbow provide primary stabilization¹, dramatically reducing the relative stress in the UCL.

My conclusion: extending the arm as much as possible prior to external rotation and prior to internal rotation is beneficial to the health of the ulnar collateral ligament.

This conclusion implies early external rotation ("early forearm turnover") and delayed internal rotation, with elbow flexion and extension occurring in between. With the arm at full extension, the timing of the forearm turnover is less important, but it should still occur before the acceleration phase instead of in the middle of it.

Dr. Marshall's pitchers use a pendulum swing to cock their arms. This is a full extension arm action that externally rotates the upper arm, engages the muscles of the flexor-pronator mass, and turns the forearm over early.  When executed properly, reverse forearm bounce does not occur.

This has obvious implications for overhand curve balls - since most pitchers are taught to throw the pitch with a flexed elbow - and less obvious implications for pitch velocity.

Kevin Millwood extending prior to internal rotation (AP Photo - Dave Pellerin)

Brandon Webb extending prior to internal rotation (AP Photo)

IN ONE PARAGRAPH

Internal rotation and the inertia that follows active external rotation both create valgus torque in the elbow. These two actions create the most torque when they are in greatest opposition to each other at the end of the cocking phase and beginning of the acceleration phase. When the elbow is flexed, this torque creates near-limit stress in the ulnar collateral ligament which leads to structural damage. To limit this stress and ensure UCL health, I draw two conclusions: (1) improve functional strength and conditioning of the flexor-pronator mass and (2) extend the arm as much as possible prior to external rotation and prior to internal rotation.

WORKS CITED

1. Cain EL Jr, Duga JR, Wolf RS, Andrews JR. Elbow injuries in throwing athletes: a current concepts review. Am J Sports Med. 2003; 31(4):621-635.
2. Conway JE, Jobe FW, Glousman RE, et al. Medial instability of the elbow in throwing athletes. Treatment by repair or reconstruction of the ulnar collateral ligament. J Bone Joint Surg. 1992; 74A:67-83.
3. Dillman C, Smutz P, Werner S, et al. Valgus extension overload in baseball pitching [abstract]. Med Sci Sports Exer. 1991; 23:S135.
4. Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med. 1995; 23:233-9.
5. Morrey BF, An KN. Articular and ligamentous contributions to the stability of the elbow joint. Am J Sports Med. 1983; 11:315-9.
6. Park MC, Ahmad CS. Dynamic contributions of the flexor-pronator mass to elbow valgus stability. J Bone Joint Surg Am. 2004; 86-A(10):2268-74.