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Wei-Yin Chen's mechanics may increase his risk of injury

Although he has proven to be durable with the Baltimore Orioles, could Chen's mechanics cause him injury in the future?

By John Butterworth
Kim Klement-USA TODAY Sports

Editor's note: Please welcome John Butterworth to our Fish Stripes! John will be doing weekly injury-related pieces and a little analysis for our site, with my input as a physician placed when needed. Here's his first piece! -MJ

Wei-Yin Chen is a strong addition to the Miami Marlins staff. Not only has he produced solid results with consistent improvement, but he has also been fairly durable.

In three out of his four years in the MLB, he started at least 30 games and pitched over 185 innings. His only trip to the DL occurred in 2013 due to a right oblique strain - he still managed to pitch 137 innings over 23 games that season. Due to his healthy MLB career, I expected Chen to have an excellent pitching delivery with sound mechanics. However, when I took a closer look, that was not the case.

Ideal pitching mechanics effectively transfer energy from the legs, to the torso, to the arm. Timing each movement perfectly is critical to minimize stress on the throwing shoulder/elbow. Research has shown that it is especially important to synchronize a pitcher's trunk/torso rotation with the throwing arm. A 2015 study in the Orthopaedic Journal of Sports Medicine at Medstar Washington Hospital Center found that early trunk rotation, defined as " trunk rotation before the stride foot hit the ground and occurrence of non-vertical arm position at initiation of trunk rotation," increases risk of shoulder and/or elbow injuries in MLB pitchers. Here is an example sketch of early trunk rotation from the 2015 paper:

Early Trunk Rotation

If the trunk begins to rotate toward home plate before the arm is vertical, there is an improper energy transfer into the throw. This can cause a pitcher to overthrow in order maintain velocity, which can be dangerous. It also causes rotational strain on the elbow and shoulder due to an excessive whipping motion of the non-vertical throwing arm, as it is forced to quickly move into a vertical position and explode through a throw. Now, have a look at this front and back still frame of Chen pitching a fastball against the Rays:

Front/back still Chen Pitching

Chen throws his fastball 55% of the time. The photos above show his typical delivery. In both pictures, you can see a dropping of the front shoulder signifying a rotation of the trunk towards home plate. However, his arm is still non-vertical. Here is a close up image from the back:



His motion is a classic example of early trunk rotation, which has been shown to be a statistically significant cause of elbow/shoulder injuries. Chen's delivery might signify a UCL or shoulder injury is in his future. In fact, he already had Tommy John surgery in 2006 during his time with Chunichi in Japan.

It is important to note that pitching mechanics analysis is still an imperfect science.  There is no "perfect delivery" that can prevent injury. While certain mechanics have shown to increase risk, each pitcher is unique. Chen's mechanics seem to be working, as he has had no serious injury since his Tommy John surgery.  Hopefully, we can expect more of the same going into the 2016 season. I'm not too worried, as he already has proven he can withstand the grind of a long MLB season.

Are you concerned with Chen's mechanics? Let us know it the comments below.

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