Does Excessive Lateral Trunk Lean Lead to Injury in Baseball

The impact of lateral trunk lean in an athlete, whether basketball player, football player or soccer player has often been speculated to have an impact on injuries.  There has been some recent data that even suggests there is also an impact on overall athletic performance.  The impact that lateral trunk lean has on injuries and performance have most often associated to the running and jumping sports (basketball, football, soccer).  That is, until now.  In the October issue of The American Journal of Sports Medicine, Oyama et al published a paper entitled “Effect of Excessive Contralateral Trunk Tilt on Pitching Biomechanics and Performance in High School Baseball Pitchers”.

Before we get into the specifics of the paper, we should first define contralateral trunk lean.  Some authors will define it as contralateral trunk lean and some as retro-trendelenburg.  For the purposes of this paper, those two terms are synonymous with one another.  Diagram A demonstrates how the authors define it in this study as it appears during the throwing cycle.  The ideal position is to “keep the head balanced over the stride foot” at maximal shoulder external rotation.  When the head is not balanced over the stride foot (as in this picture here), valgus stress at the elbow is increased.  This lateral trunk lean “not keeping head balanced over stride foot” was shown by Fleisig et al in 2006 to increase valgus load to the medial elbow.  It is this increase in valgus stress that leads to medial elbow pain and puts the athlete at risk for ulnar collateral ligament (UCL) injury.  The purpose of this study was to see if this could be observed on 2D video and  whether or not this movement resulted in greater loading to the joint and slower ball speed.

Methods:  In this study, 72 high school baseball pitchers 3-dimensional pitching biomechanics, ball speed and frontal view pitching technique was captured with both 2D cameras as well as a 3D vicon system.  Each pitcher was fitted with reflective markers and performed 5 to 10 submaximal pitches.  After warm up, each was asked to pitch as fast and as accurate as possible at an X in the strike zone. It was considered a strike if they hit the strike zone.  Each pitcher pitched until 5 qualifying pitches and minimum of 3 strike pitches were captured.  For each pitch, kinematic and kinetic data, videos and ball speed were all captured.  The point of maximal shoulder external rotation was identified and at that point, the amount of contralateral trunk lean was also identified. 

Results:  Pitchers who demonstrated excessive contralateral trunk lean pitched with a higher ball speed than those who did not (32.6 m/sec or 72.9 mph vs. 31.1 m/sec or 69.6 mph).  Those with excessive trunk lean also experienced greater proximal elbow force (103.9 N or 23.4 lbs vs. 93.2 N or 20.9 lbs) and proximal shoulder force (104.8 N or 23.6 lbs vs. 94.3 N or 21.2 lbs). There were also greater loads noted at ball release with an increase in valgus loading at the elbow and an increased shoulder internal rotation moment. 

Discussion:

Although this excessive lateral trunk lean was associated with increases in velocity, there was also an increase in loading at the shoulder and elbow.  Although, upon initial review, these load variances might not seem that significant, a 2-4 lb load increase to the shoulder and elbow joint, when done repetitively over time can lead to shoulder injuries (labral tears, rotator cuff tears, etc.) or elbow injuries (UCL tears, elbow pain, etc.). 

Although this study showed some positive performance gains (3 mph) with this altered position, there could be other factors fitting into that.  Some factors to consider are the average time of play for those who had increased speed, height and age of the players.  When looking at these factors, there is not much variance between those with trunk lean and those without.  Two other factors not mentioned in this study was if there was a previous report of injury or pain in those with trunk lean and those without and training (specifically coaching on pitching technique) amongst the two groups. 

So the question becomes, do you correct the technique at the expense of velocity.  This could and would be a hotly contested debate between clinical call (yes to decrease risk of injury) and coaching call (no as performance would suffer).  Whether right or wrong, when making that decision one must consider:

• Increased stress to the elbow and shoulder increases risk for shoulder and elbow pathology.  Injury will shorten career and have a much larger impact on long term performance.
• Lateral trunk lean or retro-trendelenburg (demonstrated above) has also been shown to increase stress to the lumbopelvic region (highlighted) and increase risk for knee pathology.
• Lateral trunk lean or retro-trendelenburg at the hip in single leg stance is commonly associated with gluteus medius and core weakness.  Improvement in strength and endurance in these areas has been shown to have a direct impact on transfer of kinetic energy. 

Considering the above, if addressed both from a coaching perspective (improving the throwing biomechanics) and addressing the strength/proprioceptive deficits, then one should see improvements in both performance as well as decreased loading to the shoulder and elbow (hence reduce risk for injury).  That considered, then core and hip strengthening could be and should be a critical component of pre-season and in season training for pitchers.

Reference:

Oyama S, Bing Y, Blackburn T, Padua D, Li L, Myers J.  Effect of Excessive Contralateral Trunk Tilt on Pitching Biomechanics and Performance in High School Baseball Pitchers.  Am J Sport Med.  41:2430-2438. 2013