Research Review #4: The Influence of Core Muscle Fatigue on Throwing Mechanics and Velocity in Adolescent Baseball Pitchers

Erickson BJ, Sgori T, Chalmers PN, et al. The impact of fatigue on baseball pitching mechanics in adolescent male pitchers. Arthrosc J Arthrosc Relat Surg. 2017;32(5):762-771. doi:10.1016/j.arthro.2015.11.051.

Background

Pitching with fatigue places adolescent pitchers at increased risk of shoulder and elbow injuries.  Adolescent pitchers who throw more than 100 innings in one season are 3.5 times more likely to be injured compared to those who throw fewer innings1.   Many adolescent pitchers continue to throw with fatigue and without respect for pitching volume recommendations.

Purpose

The purpose of this study was to determine if pitching kinematics, velocity, accuracy, and pain change in adolescent pitchers as they progress through a simulated game.

Study Population

Inclusion Criteria

  • Male pitchers, 13 to 16 years of age (n=29)

Exclusion Criteria

  • Previous shoulder or elbow surgery
  • Current shoulder or elbow injury
  • Female pitchers
  • Under 13 years of age
  • Unable to commit to completing the simulated game

Research Methods

Research participants threw a 6-inning, 90-pitch (15 pitches per inning) simulated game from a regulation mound.   A 10-pitch warm-up was performed before each inning for a total of 150 pitches thrown.  Fastballs were thrown at 100% velocity from the windup.  Velocity and accuracy were measured for each pitch.  Every 15th pitch was videotaped to assess kinematics.  Pain and fatigue were assessed after each inning with a 10-point visual analog scale.   Assessors of the videotaped pitches were blind to the research participant and the pitch count.   Pre- and post-game total arc of motion in the throwing shoulder was assessed in each pitcher.

Key Findings

  •  Fatigue increased (P < 0.001) and pitchers reported more pain (P =0.001) as pitch count increased.
  • Accuracy did not change as pitch count increased.
  • Pitch velocity significantly decreased as pitch count increased (P < 0.001).
  • Knee flexion at ball release progressively increased as pitch count increased (P= 0.008).
  • Hip-to-shoulder separation significantly decreased as pitch count increased from 90% at pitch 15 to 40% at pitch 90 (P < .001).
  • Shoulder external rotation and total range of motion increased in the dominant arm after pitching (P = .007 and P =.047, respectively).

Study Limitations

  •  Video analysis was used. Motion analysis systems may have yielded more meaningful quantitative data.
  • More meaningful kinematic changes may have been observed if pitchers were allowed to continue beyond 90 pitches.
  • A small sample size of convenience was utilized.

Practical Implications & Additional Thoughts

As pitch counts rise in adolescent pitchers, fatigue increases, pain increases, and velocity decreases.   Somewhat surprisingly, accuracy does not appear to be affected by pitch count.  Upper extremity kinematics was also unchanged as pitch count increased.  However, knee flexion at ball release increased and hip-to-shoulder separation significantly decreased with pitch number.  This may implicate lower quarter and core muscle function as a potential contributor to kinematic changes, velocity loss, and upper extremity injury from pitching.  Further prospective studies would be needed to confirm this hypothesis.

Hip-to-shoulder separation refers to the position of the hips relative to shoulder just prior to front foot contact.  Under ideal pitching mechanics, the hips are facing home plate and the shoulder continues to face towards third base.  This allows for the optimal transfer of force from the core and torso to the upper extremity.  As fatigue increases, the hips and shoulder begin to rotate in unison resulting in an open hip-to-shoulder separation.   This loss of force transfer and power generation may result in increased stress placed upon the shoulder and elbow.  During game situations, coaches should closely monitor hip-to-shoulder separation as a sign of fatigue.

These findings suggest lower quarter and core musculature fatigue before upper extremity musculature.  Therefore rehabilitation professionals and strength coaches should include training methods targeting lower quarter and torso rotation strength, endurance, and power.  Arm care exercise programs are heavily advertised and popularized over social media as a method to reduce injury risk in youth pitchers.  It is important that these programs are targeting the core musculature as well.  Medicine ball drills and multi-planar multi-joint resistance exercises should be considered when developing performance enhancement and injury prevention programs for adolescent pitchers.

References

  1. Fleisig GS, Andrews JR, Cutter GR, et al. Risk of serious injury for young baseball pitchers: A 10-year prospective study. Am J Sports Med. 2011;39(2):253-257. doi:10.1177/0363546510384224.

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