Last Updated: June 2nd, 2014
There has been a significant amount of attention paid to the perceived increase in elbow injuries in both amateur and professional baseball. With larger and larger numbers of high-profile professional pitchers going down with injuries1, the media has latched on to this specific issue this year, leading to rampant speculation on what the root causes of these injuries may be. Peer-reviewed research has so far concluded very little, though we do have some insights on what factors correlate with specific elbow injury and/or elbow valgus stress:
- Competitively pitching year-round, pitching while fatigued 2
- Increased rates of shoulder maximum external rotation 3
- Increased rates of elbow extension at ball release 4
- Increased rates of forearm supination 5
Elbow valgus stress is the primary reason that the ulnar collateral ligament (UCL, aka “Tommy John ligament”) is stretched and thereby torn, which requires reconstruction of the elbow using a tendon graft (aka “Tommy John Surgery”, “TJ Surgery”, “TJ”). This is well accepted; various research papers document this phenomenon and many physical therapy tests exists to test the integrity of the UCL, such as the moving valgus stress test6.
What hasn’t been discussed much by media outlets are the possible contributions of the surrounding musculature to help dynamically stabilize and protect the ulnar collateral ligament. However, there are significant peer-reviewed research findings that strongly suggest that the pronator-flexor mass in the medial forearm play a large role in protecting the UCL and therefore the elbow:
- Flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), and pronator teres (PT) function as dynamic stabilizers of the elbow and counter valgus stress 7, 8, 9
The American Sports Medicine Institute (ASMI) and other organizations have cautioned that breaking ball use amongst youth pitchers is not linked to increased injury10, stating:
While biomechanical research and epidemiologic research have not shown a strong connection between curveball and elbow injuries, a youth pitcher may not have enough physical maturity, neuromuscular control, and proper coaching instruction to throw a curveball with good mechanics.
However, data from a recent study11 illustrate otherwise, even if their editorialized conclusions were similar:
This chart clearly shows that throwing sliders was the single highest “risk” factor for shoulder injuries (data was not released for elbow injuries), followed up by throwing curveballs.
Additionally, data from the Driveline Baseball Sports Science Laboratory (collected via electromyographic [EMG] sensors, three-dimensional kinematic data constructed from multiple synchronized high-speed cameras, force plates) has discovered the following:
- Average kinematic differences between the slider and the fastball are significant at the elbow in a large group of high school, college, and professional pitchers – in self-identified “sliders,” peak elbow extension velocity is reached earlier in the delivery and peak angular velocity of forearm pronation is lower compared to the fastball.
- When an athlete’s throwing arm flexor-pronator mass EMG activity was significantly lower than his previous historical peak maximum isometric voluntary contraction (MVIC) test reading, subsequent bullpen sessions indicated similar peak ball velocities compared to previous sessions, but significantly worse command/control markers and significantly lower on-axis rotations per minute (RPM) on breaking balls (sliders and curveballs). Athletes often subjectively reported elbow fatigue despite being blinded to these readings prior to their bullpen sessions.
- When an athlete’s throwing arm shoulder external rotation isometric strength was significantly lower than his previous historical peak maximum isometric voluntary contraction (MVIC) test reading, subsequent bullpen sessions indicated significantly lower peak ball velocities compared to previous sessions. Athletes did not subjectively report any consistent negative feelings when reduced velocity readings were reported.
Recommendations for Collegiate and Professional Pitchers to Reduce Risk of Elbow Injury
Given the data from existing peer-reviewed research studies and new data from our lab, we are making the following recommendations that may help reduce the chance of arm injury:
- High-speed video of every pitcher should be taken from multiple angles at specific intervals and reviewed on a regular basis to detect changes to a pitcher’s mechanics over time. A biomechanical analysis by a professional may help by giving the organization and the pitcher in question specific markers to look for.
- Training staff, coaches, and players must have a unified approach to reporting injuries, pain, and other abnormalities. Pitchers should not be encouraged to pitch through pain or discomfort, and should not be penalized for reporting pain and/or discomfort. Creating an open environment where the truth can be told without fear of reprisal is paramount, and a system that tracks all incidents should be implemented.
- Kinematic and mechanical signs of fatigue during a game should be monitored on a regular basis through high-speed video sampling, radar gun readings, and location charting. If significant changes begin to appear, the pitcher should be approached as quickly as possible to discuss his symptoms and a reliever should be at the ready to replace him, if necessary.
- Year-round pitching should be avoided at all costs. Collegiate pitchers who log significant innings should skip summer baseball leagues to focus on training, while professional pitchers who log significant innings should consider skipping winter baseball for the same reasons.
- As the pronator-flexor mass dynamically stabilizes the elbow and the UCL, fitness and endurance of the FCU, FDS, FCR, and PT should be specifically targeted in a training regimen – including both general and dynamic training modalities as well as post-throwing concepts to reduce recovery time between games.
- Pitchers should be encouraged to optimize their pitching mechanics through a non-invasive training regimen that does not interfere with their ability to throw strikes with their existing arsenal of pitches. Hands-on “direct” coaching of mechanical changes should be avoided if at all possible, as research shows these changes are not likely to manifest themselves at game speeds.
- Training staff and pitching coaches should develop a between-start protocol to reduce fatigue in the pronator-flexor mass and posterior shoulder.
- Athletes with high ball velocities should pay specific attention to recovery protocols.
We feel it is irresponsible to tell coaches and pitchers to not pitch at maximum effort or to vary their ball velocities to maximize success and to reduce injury, as these recommendations lack rigorous study by the sabermetric community with regard to their effectiveness. No data exists that suggests that there is a significant correlation between pitchers who pitch at submaximal intensities and/or vary their ball velocities with increased success at any level of baseball. In fact, there exists significant data that links increased fastball velocity with both decreased runs allowed average12 and increased strikeout rate13.
References:  Tommy John Surgery List – Jon Roegele
 Olsen SJ, Fleisig GS, et al. Risk factors for shoulder and elbow injuries in adolescent baseball pitchers. (AJSM 2006)
 Sabick MB, Torry MR, et al. Valgus torque in youth baseball pitchers: A biomechanical study. (JSES 2004)
 Aguinaldo A, Chambers H. Correlation of Throwing Mechanics With Elbow Valgus Load in Adult Baseball Pitchers. (AJSM 2009)
 Buffi J, Murray W. Effect of Forearm Posture on the Elbow Varus Torque Generated by the Flexor Pronator Muscles: Implications for the Ulnar Collateral Ligament. (pending)
 Moving valgus stress test of the elbow – YouTube
 Lin F, Kohli N, et al. Muscle contribution to elbow joint valgus stability. (JSES 2007)
 Park MC, Ahmad CS, et al. Dynamic contributions of the flexor-pronator mass to elbow valgus stability. (JBJSA 2004)
 Udall JH, Fitzpatrick MJ, et al. Effects of flexor-pronator muscle loading on valgus stability of the elbow with an intact, stretched, and resected medial ulnar collateral ligament. (JSES 2009)
 ASMI Tommy John Position Statement
 Little League / University of North Carolina Department of Exercise and Sports Science: The Learning Curve Five-Year Study (pdf)
 Fast, M. Lose a tick, gain a tick. (Hardball Times 2010 – web link)
 Cameron, D. Velocity and K/9. (Fangraphs 2009 – web link)