Loss of Shoulder Horizontal Adduction ROM Influences Shoulder and Elbow Forces During Throwing

Laudner KG, Wong R, Evans D, Meister K. The effects of restricted glenohumeral horizontal adduction motion on shoulder and elbow forces in collegiate baseball pitchers. J Shoulder Elbow Surg. 2021;30(2):396-400. doi:10.1016/j.jse.2020.05.029

The posterior deltoid and posterior rotator cuff work together to eccentrically control the arm during the deceleration phase of throwing.  Posterior shoulder tightness (PST) can result in a loss of glenohumeral (GH) internal rotation (IR) and/or horizontal adduction range of motion (ROM).  It is theorized that PST leads to excessive stress to the shoulder and elbow during baseball pitching. 

Purpose

The primary purpose of this study was to investigate how restricted GH horizontal adduction ROM affects upper extremity forces during throwing in collegiate baseball pitchers.

Study Methods

A sample of 55 asymptomatic NCAA Division I baseball pitchers volunteered to participate. Pitchers with –10 degrees or less of horizontal adduction ROM were assigned to the restricted ROM group.   Pitchers with more than –10 degrees of horizontal adduction ROM were assigned to the control group.  All participants had no history of injury within the last 3 months and no previous shoulder or elbow surgery.

GH horizontal adduction ROM measurements were made with the participants supine . One examiner stabilized the lateral border of the scapula. This examiner used their other hand to passively move the arm into horizontal adduction while maintaining the GH joint in neutral rotation. At the end range of motion, a second examiner aligned a digital inclinometer with the humeral shaft to determine the angle between the humerus and a vertical reference created by the inclinometer.  

GH IR, external rotation (ER), and total arc of motion were passively measured from the supine position.

Motion analysis with 26 reflective markers was captured for each participant.  Each participant threw 5 fastball trials at maximum effort from a standard height mound.  The average of 3 fastballs thrown for strikes, with the highest ball velocities were used for analysis.

All forces were normalized to each individual pitcher’s body weight for distraction forces and to their respective body weight x height for torques.

Key Results

  • Both groups presented with significant bilateral differences in their total arcs of motion (P <.04). This suggests that the loss of horizontal adduction in these groups was at least partially due to soft tissue tightness.
  • There were no significant between-group differences for shoulder external rotation torque or shoulder and elbow distraction (P >.10).
  • Compared to the control group, the restricted ROM group had significantly more shoulder abduction torque (P = 0.04), shoulder horizontal abduction torque (P = 0.004), elbow flexion torque (P = 0.002), and elbow valgus torque (P = 0.002).

PST is Associated with Increased Shoulder and Elbow Torque During Baseball Pitching

Baseball pitchers with less than -10 degrees of GH horizontal adduction ROM produce greater shoulder and elbow torques during the deceleration phase of throwing.  This includes shoulder abduction torque, shoulder horizontal adduction torque, elbow flexion torque, and elbow valgus torque.

Previous research suggests PST in baseball players is associated with scapula malposition1.   Scapula malposition could theoretically cause the baseball pitcher to lead with the shoulder during the acceleration phase of throwing.  As a result the arm lags behind the shoulder causing an increase in shoulder horizontal abduction torque.  Other research has also linked PST to excessive elbow valgus torque in youth baseball players2.

Both groups presented with significant bilateral differences in their total arcs of motion. The researchers hypothesized that the loss of IR without a concomitant increase in ER that typically accompanies bony adaptation suggests at least some soft tissue PST in both groups.  However, this cannot be confidently concluded based on the available data presented in this article.

The principle finding of this study suggests strength and rehab professionals should intervene in the presence of PST in baseball pitchers.  Passive stretching3, soft tissue techniques3, and PNF techniques4 are typically effective for managing this impairment in overhead athletes.  I have found the combined approach of instrumented assisted soft tissue mobilization and stretching described by Bailey et al3 to be very effective.  Horizontal adduction stretching performed in side-lying with the scapula stabilized is my preferred approach.

Please share your preferred interventions to manage PST and/or loss of horizontal adduction ROM in the overhead athlete.

References

  1. Laudner KG, Moline MT, Meister K. The relationship between forward shoulder posture and posterior shoulder tightness among baseball players. Am J Sports Med. 2010;38(10):2106-2112. doi:10.1177/0363546510370291
  2. Sabick MB, Torry MR, Lawton RL, Hawkins RJ. Valgus torque in youth baseball pitchers: a biomechanical study. J Shoulder Elbow Surg 2004;13:349-55. https://doi.org/10.1016/j.jse.2004.01.013
  3. Bailey LB, Thigpen CA, Hawkins RJ, Beattie PF, Shanley E. Effectiveness of manual therapy and stretching for baseball players with shoulder range of motion deficits. Sport Heal A Multidiscip Approach. 2017;9(3):230-237. doi:10.1177/1941738117702835
  4. Reed ML, Begalle RL, Laudner KG. Acute effects of muscle energy technique and joint mobilization on shoulder tightness in youth throwing athletes: A randomized controlled trial. Int J Sports Phys Ther. 2018;13(6):1024-1031. doi:10.26603/ijspt20181024

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