Why Baseball Players Get UCL Injuries: 7 Risk Factors Every Player Should Know
For baseball pitchers, few injuries are more feared than a UCL injury.
The ulnar collateral ligament (UCL) is located on the inside—or medial side—of the elbow and plays an important role in resisting the tremendous forces created during throwing. When a pitcher throws a baseball at high velocity, the elbow is exposed to significant valgus stress, which attempts to “open” or gap the inside of the elbow.
Over time, repeated exposure to these forces can contribute to ligament damage.
But UCL injuries are rarely caused by one single factor.
As a Pittsburgh physical therapist who specializes in baseball performance, throwing athletes, and arm care, I look at UCL injury risk as a multifactorial problem. Pitch velocity, workload, recovery, mechanics, mobility, pitch selection, and lower-body function can all influence how much stress ultimately reaches the elbow.
Here are seven UCL injury risk factors every baseball player, parent, coach, and pitcher should understand.
1. High Pitch Velocity
Everyone wants to throw harder.
And for good reason—velocity is an important part of pitching performance.
But throwing harder also means your body has to produce and tolerate greater forces.
Research has consistently demonstrated a relationship between increased pitch velocity and increased elbow kinetics, including elbow varus torque. In other words, as a pitcher produces more velocity, the forces acting on the elbow can increase as well. (PubMed)
This is important because the UCL helps resist the valgus stress created during the pitching motion.
Think of it this way:
More velocity → greater force production → greater stress on the throwing arm.
That doesn’t mean pitchers should avoid throwing hard. In fact, developing velocity is an important part of baseball development.
The goal is to develop velocity without asking the elbow to absorb more stress than the rest of the body can handle.
This is where strength training, mechanics, workload management, and physical preparation become extremely important.
It’s also worth noting that velocity alone does not explain every UCL injury. Research has found mixed results when looking at velocity as an independent predictor of UCL reconstruction. The relationship between velocity and elbow stress, however, is much more consistent. (PubMed)
2. High Throwing Workload
One of the biggest mistakes I see in baseball is going from very little throwing to a lot of throwing very quickly.
The UCL doesn’t just care about how hard you throw.
It also cares about how often you throw.
Every pitch exposes the elbow to stress. Repeated exposure without adequate preparation or recovery can increase the overall load placed on the throwing arm.
Research examining UCL injuries has identified increased pitch counts and throwing volume as important potential risk factors. (PubMed)
This is why workload management matters.
A pitcher shouldn’t go from:
Low throwing volume → suddenly high throwing volume
Instead, workload should be gradually developed.
During the offseason, for example, a pitcher may intentionally reduce throwing volume before gradually building it back up. As the season approaches, throwing can be organized around different levels of intensity:
Low-intent throwing days
Moderate-intent throwing days
High-intent throwing days
Bullpen days
Competition
The goal isn’t simply to throw less.
The goal is to prepare the body to tolerate the amount of throwing the athlete is eventually going to ask it to do.
3. Insufficient Recovery Between Throwing Exposures
Workload and recovery go hand in hand.
A pitcher who throws a high volume of pitches but has adequate time to recover is in a different situation than a pitcher who repeatedly throws hard with minimal recovery.
Fatigue matters because pitching is a full-body movement.
As the legs, trunk, shoulder, and forearm fatigue, the athlete may have more difficulty maintaining the same movement strategy. Research examining pitching biomechanics has identified fatigue and altered mechanics as potential contributors to increased upper-extremity stress. (PubMed)
This is one reason I emphasize building the physical qualities that help pitchers recover and tolerate throwing.
That includes:
Forearm strength
Grip strength
Finger strength
Shoulder strength
Rotator cuff capacity
Scapular strength
Trunk strength
Lower-body strength
The goal is to give the pitcher more places to produce and absorb force so the elbow isn’t doing all of the work.
For younger pitchers especially, adequate rest between pitching exposures is an important part of arm-health management. (PubMed)
4. Poor Pitching Mechanics
Pitching is a kinetic chain.
Force starts from the ground and moves through the legs, pelvis, trunk, shoulder, elbow, and finally the hand and baseball.
When one part of that chain isn’t doing its job effectively, another part may have to compensate.
For example, if the arm is late relative to the rest of the body when the front foot hits the ground, the pitcher may rely more heavily on the arm to generate velocity.
Certain biomechanical characteristics—including timing of trunk rotation, shoulder position, arm position, and release mechanics—have been associated with increased elbow kinetics and injury risk. (PubMed)
Release position matters as well.
One study of MLB pitchers found that pitchers who eventually underwent UCL reconstruction demonstrated a more lateral horizontal release position compared with matched controls. (PubMed)
This doesn’t mean there is one perfect pitching motion for every athlete.
Instead, it means we should evaluate how the individual athlete moves and determine whether their mechanics are creating unnecessary stress.
Good mechanics aren’t about making every pitcher look identical.
They’re about creating an efficient way to produce velocity while managing stress throughout the kinetic chain.
5. Inadequate Shoulder Mobility
The shoulder plays a huge role in protecting the elbow.
Pitchers naturally develop adaptations in shoulder range of motion over time, so the goal isn’t necessarily to make a pitcher’s shoulder look exactly like a non-throwing athlete’s shoulder.
One measurement I like to look at is total arc of motion, which considers both internal and external rotation.
Research has identified relationships between decreased shoulder range of motion and UCL injury risk, although the evidence isn’t perfectly consistent across every study. (PubMed)
That’s why I don’t believe every pitcher simply needs to “stretch their internal rotation.”
Instead, we should ask:
Does this athlete have adequate, usable shoulder motion for their throwing demands?
If the shoulder is excessively restricted, the body may have to find motion somewhere else.
And when we’re talking about a high-speed movement like pitching, that compensation can ultimately affect the elbow.
Monitoring shoulder mobility throughout the season can also be valuable. Research has demonstrated meaningful changes in shoulder and hip range of motion across a professional baseball season. (PubMed)
6. Limited Pitch Repertoire
Pitch selection is another factor worth considering.
If a pitcher throws an extremely high percentage of one pitch—particularly the fastball—the same movement pattern and loading strategy are repeated over and over.
One MLB study found that pitchers who underwent UCL reconstruction threw a significantly higher percentage of fastballs than matched controls. The study found that each 1% increase in fastball usage was associated with approximately a 2% increase in UCL injury risk, although this should not be interpreted as proof that throwing a fastball directly causes a UCL injury. (PubMed)
A broader systematic review also identified a higher percentage of fastballs and a smaller pitch repertoire as potential UCL injury risk factors. (PubMed)
Think about it like strength training.
If you went into the gym every day and performed the exact same exercise with the exact same loading strategy, you’d repeatedly stress the same tissues.
Pitching is similar.
A well-developed repertoire can expose the body to different movement and loading demands.
Depending on the athlete’s age, development, and skill level, that may include pitches such as:
Fastball
Changeup
Slider
Curveball
Other off-speed pitches
Pitch selection should always be appropriate for the athlete’s age and development, but having variety can be an important part of long-term pitching development.
7. Poor Lower-Body and Lower-Extremity Function
This is one of the most overlooked pieces of the puzzle.
Pitchers don’t throw with their arms. They throw with their entire body.
The lower body generates force that is transferred through the pelvis and trunk before ultimately reaching the throwing arm.
If a pitcher lacks adequate lower-body strength, single-leg stability, hip mobility, or pelvic control, the upper extremity may have to compensate.
One area I pay close attention to is single-leg stability.
During pitching, the athlete has to control their body on one leg while transferring force toward home plate. If the athlete cannot control the pelvis and trunk effectively, the throwing arm may have to compensate.
Hip mobility is important as well.
Research has demonstrated relationships between hip characteristics and upper-extremity injuries in baseball pitchers, and professional pitchers have also been shown to experience changes in hip range of motion throughout a season. (PubMed)
This is why a good arm-care program shouldn’t just be an “arm” program.
We should also be training:
Single-leg strength
Hip strength
Hip rotation
Glute strength
Trunk control
Balance
Lower-body power
The stronger and more efficient the entire kinetic chain is, the more opportunities the athlete has to distribute force instead of repeatedly asking the elbow to handle it.
UCL Injuries Are Multifactorial
Here’s the most important takeaway:
There is no single exercise, stretch, pitch-count number, or mechanical adjustment that can guarantee a pitcher won’t suffer a UCL injury.
UCL injuries are multifactorial.
Some risk factors are modifiable. Others aren’t.
But there are plenty of things we can work on.
We can monitor throwing volume.
We can progressively build workload.
We can develop shoulder, forearm, and grip strength.
We can improve lower-body strength and single-leg stability.
We can monitor mobility.
We can evaluate pitching mechanics.
We can make sure athletes aren’t constantly throwing at maximum intent without adequate preparation and recovery.
And we can pay attention to changes in performance, velocity, soreness, and movement quality.
The goal isn’t to eliminate every possible risk.
The goal is to make the athlete as physically prepared and resilient as possible.
I often tell athletes:
The only way to completely avoid a baseball injury is to stop playing baseball.
Obviously, that’s not what we’re trying to do.
We want athletes to play the sport they love.
Our job is to help them stay healthy enough to keep playing it.
How Can a Baseball Physical Therapist Help?
At Undefeated Physical Therapy & Performance in Pittsburgh, PA, we work with baseball players of all levels, from youth athletes to high-level pitchers, focusing on throwing performance, arm health, strength, mobility, and return-to-play.
A comprehensive baseball physical therapy evaluation can help identify limitations in areas such as:
Shoulder strength and mobility
Elbow and forearm strength
Grip strength
Hip mobility
Single-leg stability
Lower-body strength
Trunk control
Throwing mechanics
Workload and throwing history
If you’re a baseball player in Pittsburgh, Washington County, or the surrounding Western Pennsylvania area looking to improve your arm health, build strength, or reduce your risk of throwing-related injuries, I’d be happy to help.
Dr. Carmen Jansante, PT, DPT, CSCS Undefeated Physical Therapy & Performance Pittsburgh, PA
📞 Call or text: 412-627-2131
📧 Email: Carmen@undefeatedpt.com
📱 Instagram: @undefeated_pt
Your arm doesn’t need to be broken before you start taking care of it.
Build it. Train it. Protect it. Keep playing.
References
Camp CL, et al. Increased Pitch Velocity Is Associated With Throwing Arm Kinetics, Injury Risk, and Ulnar Collateral Ligament Reconstruction in Adolescent, Collegiate, and Professional Baseball Pitchers: A Qualitative Systematic Review. Arthroscopy. 2023. (PubMed)
Koo JH, et al. A Number of Modifiable and Nonmodifiable Factors Increase the Risk for Elbow Medial Ulnar Collateral Ligament Injury in Baseball Players: A Systematic Review. Arthroscopy. 2023. (PubMed)
Chalmers PN, et al. The Relationship Between Pitching Mechanics and Injury: A Review of Current Concepts. Sports Health. 2017. (PubMed)
Aguinaldo AL, et al. Baseball Pitching Biomechanics in Relation to Injury, Pain, and Surgery: A Systematic Review. Sports Health. 2020. (PubMed)
Erickson BJ, et al. Risk Factors for an Ulnar Collateral Ligament Injury Resulting in Surgery: A Prospective Longitudinal Study of 305 Professional Baseball Pitchers. 2025. (PubMed)
Whiteside D, et al. Major League Baseball Pitch Velocity and Pitch Type Associated With Risk of Ulnar Collateral Ligament Injury. American Journal of Sports Medicine. 2016. (PubMed)
Sgroi T, et al. Influence of Pitching Release Location on Ulnar Collateral Ligament Reconstruction Risk Among Major League Baseball Pitchers. American Journal of Sports Medicine. 2019. (PubMed)
Iwamoto J, et al. Relationship Between Upper Limb Injuries and Hip Range of Motion and Strength in High School Baseball Pitchers. 2021. (PubMed)
Chan JM, et al. Upper Extremity and Hip Range of Motion Changes Throughout a Season in Professional Baseball Players. American Journal of Sports Medicine. 2020. (PubMed)
Chalmers PN, et al. Athletic Hip Injuries in Major League Baseball Pitchers Associated With Ulnar Collateral Ligament Tears. 2018. (PubMed)
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