Flexor Pronator Strains and Forearm Pain After Throwing - What’s Really Going On?

Many athletes will experience anterior forearm pain during or after throwing at some point in their career. Medically, they may be diagnosed with a “flexor pronator” strain. The pain may persist into the medial elbow, and eventually damage to the ligamentous structure at the medial elbow, the UCL itself.

Throwing a baseball at high speeds will inherently be done with some level of compensation throughout the system, including the shoulder, elbow, wrist and hand. It is not possible to throw a baseball 90MPH with relative motions. Therefore, avoiding the risk of injury all together is unlikely.

Here’s what we can do:

• Useful strategies can be implemented to limit the amount of compensation.

• Training decisions can be made, acknowledging the possibility of second and third order consequences.

First, it is helpful to understand the likely adaptions that take place at the shoulder, elbow, wrist, and hand as a consequence of throwing. These adaptations are advantageous to a degree. Taken to an extreme, they can often be influencing the pain and / or injury.

Lets consider the actual position of the arm, at various sections relative to each other, in space. In the aftermath of injury, muscles are often blamed for being “weak” rather than disadvantaged positionally to create force at various times.

Muscles have varying ability to create force dependent on their length. For example, take your biceps. At end range traditional elbow extension, and traditional flexion the biceps are relatively weaker (or less able to create force) than they are at 90deg of traditional elbow flexion. The orientation of a muscle influences joint position. A muscle can be more eccentrically oriented (lengthened relative to an imaginary neutral point), or more concentrically oriented (shorter relative to an imaginary neutral point). A change in the muscle’s orientation is required to change the actual position of a segment relative to another segment.

Connective tissue behavior at that area may be more overcoming (force producing) or yielding (energy storage) regardless of the orientation of the muscle itself. It’s important to acknowledge this difference. A muscle may be eccentrically oriented, but producing force if the connective tissue behavior is overcoming.

You can still move through space without relative changes in joint position. Movement in this case is influenced by changes in connective tissue behavior, and / or, large segments are moving together (called an orientation); their position in space is driven by what CAN still move. For example, when the muscles at the pelvis do not change orientation, the bones of the pelvis can not move relative to one another. However the spine may still be able to change shape, and the pelvis will move as a unit relative to the spinal position. As an example, traditional spinal extension can orient the pelvis downwards as a compensation to put force into the ground (IR).

Furthermore, bones are still soft tissue, although relatively less soft than other tissue in the body. Therefore bones can, and do change shape all the time. They are designed to do so. Strong orientations can effectively twist and bend bones in the body if the influence of the muscle orientation and connective tissue behavior is strong enough.

In the case of the throwing arm, we often see all of these at play. Adaptions occur due to several factors including structure and demands. In the case of a thrower experiencing anterior / medial forearm pain here’s what can be going on.

First the humerus is proximally turned into ER by design. More so in some individuals than others. Throwing, further twists the proximal humerus into ER. Thanks to Bill Hartman, a great analogy is that of a towel. Take a towel and grip it at two ends. Turn the top of the towel into ER a few times, that’s where it typically rests by design. You will notice while doing so the bottom hand did not move. Therefore, it can be said that the proximal humerus is in ER relative to the distal humerus (which can be said to be in relative IR). Continue twisting the top hand into ER until the towel becomes stiffer and stiffer, at a certain point any additional twist of the top hand will begin to influence to bottom hand. No longer do we have relative movement. Instead we are orienting the entire humerus into ER.

Appreciate that this relationship can happen at the axial skeleton as well. When we have no more relative movement available we can orient the axial skeleton to get the arm further back as well. Now appreciate that if the distal humerus continues to orient into ER it can eventually bring the proximal forearm with it as well. This in turn can cause the same thing to happen at the wrist, and then the hand. However, in the case of throwing, or even lifting, where the hand is also acting on an object (the ball or a barbell) the wrist can compensate for the lack of IR through the system. When throwing, we can begin working harder at the wrist and then eventually the hand to pronate or IR. When holding a barbell our hand and wrist are “fixed” and create an opposing resistance against the ER up the arm.

In turn this causes a shape change in the bones themselves. The humerus is twisted into ER, more so proximally, and the radius is twisted into ER proximally and IR distally. The muscles are along for the ride sort to speak, wrapping helically around the bones based on their relative attachments. Muscles that span two joints can acquire different orientations at the proximal and distal portions with possible different connective tissue behavior as well.

For example in this case, a diagnosed “flexor pronator strain” the Flexor Carpi Radialis (FCR) and the Flexor Carpi Ulnaris (FCU) are looped together based on their common attachment to the common flexor tendon. However, the proximal portions of these muscles are eccentrically oriented to allow for the excess twist of the elbow into ER, and the distal portions of these muscles are concentrically oriented (likely more so at the FCR). This creates a pretty big twist in opposing directions, and a proximal portion that is disadvantaged to create force.

As the arm moves from maximally laid back (ER) towards extension (IR) the anterior forearm muscles are not in a favorable position to help close the medial elbow. Is it because they aren’t strong enough, or is it because they are not in a position to create maximal force?

If we accept that the arm is twisted into ER, the elbow is twisted into ER and the hand / wrist are twisted relatively into IR (in some cases with the hand relatively further into IR than the wrist) then we can acknowledge a shortcoming in approaches that center around furthering the output, rather than influencing the relationship between segments. For example:

More grip strength? So more hand and wrist IR?

More pronation at the hand and wrist? So try and twist further into IR orientation?

More forearm strength? How are you going about this, by pronating the hand and wrist, by supinating the hand and wrist and not accounting for movement into ER at the proximal forearm?

More rotator cuff strength? More rowing strength? Further compressing the posterior space at the shoulder and thorax, and driving more orientation of the shoulder and thorax into ER?

It just doesn’t add up. At best, you’re buying time to uphold a less than favorable strategy.

Instead maybe we need to address the position, and in turn change the strategy. We need to untwist the towel back closer to where it came from.

We need to supinate the hand and wrist relative to the proximal forearm. We need to IR the proximal forearm relative to the distal humerus. We need to untwist the humerus. We need to address the shoulder and axial skeleton and gain the ability to express actual relative IR.

After this, we can play with output, and challenge the system to hold more favorable positions / relationships. This can be done by acknowledging the seven components of force relative to throwing (tip of the cap to Dr. Jen Reiner). The location (1) and direction (2) of force specific to throwing should be held relatively constant, while adjusting the dials on rate (3), magnitude (4), variability (5), frequency (6), and duration (7).

Additionally, we need to acknowledge that some of the activities we use in general preparation may have consequences down the line. Are we causing too much compression in the dorsal rostral space? Reaching activities may be more beneficial than pulling activities and common “arm care exercises” such as I’s, T’s, and Y’s. Reaching promotes an expansion of the DR space, while the latter lays down further compression.

Can we stay away from using implements that fix the hand into pronation while promoting an ER strategy up the arm? For example, staying away from traditional barbell exercises, and bi-lateral presses and rows. Instead utilizing DB’s, KB’s and Cables. Pay attention to grip styles, and the amount of “squeeze” that is need to hold the implement. Looser grips, open hand grips, and bottom’s up grips all scale down the amount of motor output.

Lastly, I want to point out that mechanics of throwing should not be overlooked. The way an athlete throws can certainly be a factor in the equation. Make sure you are evaluated mechanically by a coach you can trust.

I hope this can offer a different perspective. If you found this post useful, or know someone who might find value in it, please feel free to share!