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Pitcher Injury Mechanisms

In Pitching MRSA and Killer Cues, I identify some of the movement patterns that I believe are contributing to the pitcher injury epidemic. However, the question is what exactly is causing the injuries.

Timing Problems

As I mention in It's the Timing, Stupid, a 2012 study entitled Early Cocking Phase Mechanics by Dr. Weimi Douoguih, Medical Director for MedStar Sports Medicine and Medical Director for the Washington Nationals, suggests that the problem with the Inverted W isn't the position itself as much as the timing problem that the Inverted W tends to create.

The logic is that, by having the pitching arm side forearm at or even below the horizontal (low to negative degrees of external rotation) at the moment the front foot plants and the shoulders start to rotate, the greater the amount and force with which the pitching arm will externally rotate. That will increase the load on the muscles, enabling the pitcher to throw harder but placing more stress on the shoulder and the elbow.

Anthony Reyes

Anthony Reyes

The farther the pitching arm is from 90 degrees of external rotation at the moment that the front foot plants and the shoulders start to rotate, the greater the load and the stress on the arm.

Bob Gibson

Bob Gibson

In contrast, the closer that pitchers' arms are to 90 degrees of external rotation -- vertical forearm, as when giving a high five -- at the moment that their front foot plants, the less likely it is that their pitching arm will be overloaded.

Premature Pronation

If you study the anatomy of the elbow, you will find that the load that is placed on the elbow during a 85+ MPH pitch exceeds the strength of the Ulnar Collateral Ligament (UCL). That means that some of the load is being carried by some other structure in the elbow.

Dr. Mike Marshall theorized that the load above the UCL failure point is carried by the Pronator Teres muscle. The Pronator Teres also inserts into the Medial Epicondyle and passes over the UCL. However, recent research suggests that the load is more likely borne by a different set of muscles that arise from the Medial Epicondyle.Park 2004, Udall 2009

Regardless of exactly what muscles are involved, the idea is that, for the load to not be focused on the UCL, pitchers need to be activating those critical muscles during the moment that the UCL is under maximum stress.

The theory is that the problem with cues like Show the Ball to Center Field, Keep Your Fingers on Top of the Ball, and many of the other cues that are used to teach throwing is that they put the forearm in a position of premature pronation and activate the muscles that arise from the Medial Epicondyle too early. At the moment when these muscles are needed to help carry some of the load, these muscles are relaxing. That forces the UCL to carry more of the load and causes it to degrade more quickly.

This theory is backed up by findings of scientific studies, including Udall's comments on Ahmad 2003 in which he states, "Electromyographic studies of the flexor-pronator muscles have shown that these muscles may actually fire less in pitchers with MUCL deficiency."Udall 2007 Udall also states elsewhere, "Although the arm and forearm musculature are not large contributors to force generation during throwing motion, they play important roles in the accuracy and control in overhead throwing athletes. The flexor-pronator muscles also play a role in the stability of the elbow joint to valgus stress..."Udall 2009


Ahmad 2003. Ahmad, Christopher S., Lee, TQ, ElAttrache, N.S. "Biomechanical Evaluation of a New Ulnar Collateral Ligament Reconstruction Technique with Interference Screw Fixation." American Journal of Sports Medicine 31:332-227, 2003.

Park 2004. Park, Maxwell C. and Ahmad, Christopher S. "Dynamic Contributions of the Flexor-Pronator Mass to Elbow Valgus Stability." Journal of Bone and Joint Surgery 86:2268-2274, 2004.

Udall 2007. Udall, John H., Fitzpatrick, Michael J., McGarry, Michelle H., Leba, Thu-Ba, and Lee, Thay Q. EFFECTS OF FLEXOR-PRONATOR MUSCLES ON VALGUS STABILITY OF THE ELBOW. 53rd Annual Meeting of the Orthopaedic Research Society, 2007. Poster Number 1154.

Udall 2009. Udall, John H., Fitzpatrick, Michael J., McGarry, Michelle H., Leba, Thu-Ba, and Lee, Thay Q. "Effects of flexor-pronator muscle loading on valgus stability of the elbow with an intact, stretched, and resected medial ulnar collateral ligament" Journal of Shoulder Elbow Surgery 18:773-778, 2009.

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