Research Review #2: Trunk Strength and Throwing Mechanics in Youth Pitchers

Oyama S, Waldhelm AG, Sosa AR, Patel RR, Kalinowski DL. Trunk muscle function deficit in youth baseball pitchers with excessive contralateral trunk tilt during pitching. Clin J Sport Med. 2017;27(5):475-480. Link to Abstract

Background

Excessive contralateral trunk tilt (CLT) during baseball pitching has been associated with increased loading at the shoulder and elbow which may predispose these joints to injury.  High school pitchers with excessive CLT demonstrate increased shoulder external rotation torque, shoulder distraction force, and elbow valgus torque1.  As the trunk leans away from the throwing shoulder during the arm-cocking and acceleration phases of pitching, the oblique muscles on the dominant side eccentrically control CLT.  Trunk muscle weakness may be one contributing factor to faulty pitching mechanics and subsequent upper extremity joint stresses.

Purpose

 To test the association between trunk muscle weakness and excessive CLT by comparing trunk muscle strength among youth baseball pitchers who demonstrate varying degrees of CLT.

 Study Population

 Inclusion Criteria

  • Minimum of 3 months of baseball pitching experience
  • No history of injury within the past 6 months
  • Ages 8 to 11 (n=28)

Exclusion

  • Pitchers who pitched and hit on the other side (e.g., right pitcher who is a left hitter)

Research Methods

Research participants were evaluated with video analysis and a radar gun for three pitched strikes from a mound at a distance of 46 feet.   The CLT angle was calculated as the angle of the vector extending from the xiphoid process to the sternal notch relative to vertical.  Pitchers whose CLT was less than 15 degrees, between 15 and 30 degrees and greater than 30 degrees were categorized into low, moderate, and high CLT groups, respectively.  Trunk strength was measured with a dynamometer for trunk rotation, extension, and flexion.  Maximum forces were normalized to each participant’s body weight.

 Key Results

  •  High CLT was associated with greater pitching experience and greater ball speed
  • High CLT was associated with lower trunk rotation strength ratios
    • Pitchers with low CLT: Trunk rotation strength in the direction towards the dominant side was 111.4% of the strength towards the nondominant side
    • Pitchers with high CLT: Trunk rotation strength in the direction towards the dominant side was 82.8% of the strength towards the nondominant side

Study Limitations

  • Due to its cross-sectional nature, no cause-and-effect relationship can be established between trunk rotation strength and CLT
  • EMG analysis during pitching would help elucidate the researcher’s hypotheses about specific abdominal muscle imbalances (i.e., weakness of the internal oblique)
  • Video analysis was used to calculate throwing mechanics and CLT. Three-dimensional motion analysis may have offered more meaningful quantitative data.

Practical Implications & Additional Thoughts

Pitchers who demonstrated high CLT (>30 degrees) presented with weakness in trunk rotation strength towards the dominant side.    These researchers propose that trunk muscle imbalances may be associated with relative weakness of the internal oblique on the dominant side.  This hypothesize requires validation through further research.  Regardless of isolated muscle imbalances, these findings support the role of including bilateral trunk rotation strength and power exercises for youth pitchers.  Medicine ball drills and traditional anterior core exercises, such as lifts and chops, should be trained from both dominant and nondominant sides to minimize the imbalance created through repetitive throwing.

Pitchers with high CLT were also characterized by greater pitching experience and ball speed.  This suggests that youth pitchers may learn to generate greater ball velocities through increasing CLT with experience.  This has the potential to create and perpetuate any trunk muscle imbalances.  It is important that youth pitchers develop proper pitching technique early during their playing years in order to minimize the deleterious upper extremity joint stress which may appear with physical maturation.

This research stresses the importance of fundamental pitching instruction during the early playing years.  Along with proper instruction, early integration of fundamental trunk strengthening exercise may minimize or prevent trunk muscle imbalances which could predispose the youth pitcher to future upper extremity injury.

References

  1. Oyama S, Yu B, Blackburn JT, Padua DA, Li L, Myers JB. Effect of excessive contralateral trunk tilt on pitching biomechanics and performance in high school baseball pitchers. Am J Sports Med. 2013;41(10):2430-2438. doi:10.1177/0363546513496547.

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