Research Review #7: An Analysis of Youth Pitching Mechanics

Thompson SF, Guess TM, Plackis AC, Sherman SL, Gray AD. Youth baseball pitching mechanics: A systematic review. Sport Heal A Multidiscip Approach. 2017; Ahead of Print:1-8. doi:10.1177/1941738117738189 .

Background

Youth baseball pitching injuries are on the rise.  Common causes of this increase include improper pitching mechanics, pitching year-round and playing on multiple teams.  Biomechanical studies investigating the pitching motion and its association with injury have been conducted primarily on collegiate and professional baseball players.  However, little attention has been given to investigating these factors in youth baseball players.  The normal pitching motion of healthy youth pitchers should first be established before abnormal pitching motions and their relationship to injury can be determined.

Purpose

The purpose of this study was to systematically review the literature and provide a summary of the normal ranges of kinetic and kinematic values for the upper and lower body during the youth baseball pitching motion.

Research Methods

Include Original Studies

  • Published in English through February 2017
  • Described biomechanics of normal youth baseball pitching motion or compared the mechanics of pitch types
  • Research participant ages was ≤ 13 years

Ten original studies met the inclusion criteria and were included in this review.  Comparisons of biomechanics were organized by positional parameters at various time points in the pitching cycle and throughout pitch cycle phases.  Joint torques at various time points in the pitching cycle and throughout pitch cycle phases, and maximum angular velocities reached when throwing the fastball were also retrieved from the original studies.  Individual data points were extracted from each study to compare all measured parameters, and the data were then aggregated to present an overall range from the included studies

Key Results

  • Maximal shoulder external rotation (ER) ROM occurs during the late cocking phase at 166-178.2 degrees.
  • Following maximal ER the shoulder internally rotates to a maximum of 13.2 to 17 degrees at the end of arm deceleration
  • Elbow valgus torque reaches its maximal level (18 ± 4 N·m) just prior to maximum shoulder ER and decreases throughout the remainder of the pitch cycle.
  • A pitcher’s weight is the biomechanical factor most closely correlated with the magnitude of valgus torque and has also been correlated with elbow injuries.
  • Stride length is 66% to 85% of pitcher height.
  • Compared with the fastball, throwing a curveball demonstrates less elbow varus torque (31.6 ± 15.3 vs. 34.8 ± 15.4 N·m).
  • The primary differences between youth and adult pitching biomechanics relate to maximal angular velocities at the shoulder and elbow.

Study Limitations

  • Little research has been conducted investigating biomechanical parameters of the lower body in healthy youth baseball players.
  • The majority of biomechanical studies included in this review were conducted in laboratory settings. Results may differ when live-game settings are investigated.

Practical Implications & Additional Thoughts

Proper youth pitching mechanics should be given priority over all performance-based measures during the early years of baseball.  Youth pitchers who do not achieve a baseline level of proficiency with their pitching mechanics will find it increasingly challenging to correct faulty patterns later in their career.  Poor mechanics can lead to increased forces on joints, bones, and soft tissues making the youth athlete susceptible to injury.   This systematic review helps elucidate several important biomechanical parameters of the youth pitching motion.

Maximal shoulder ER and maximal elbow valgus torque occur during the late cocking phase of throwing.  Many injured throwers experience pain during this phase of the pitching cycle.  Ensuring youth pitchers are able to achieve the necessary position of maximal shoulder ER may help reduce torque at the elbow.  Other important factors not investigated in this review include thorax mobility and control of the lumbopelvic-hip complex.  These proximal factors can influence the kinetic chain and when compromised increased demands will be placed on the shoulder and elbow.  For example, increases in contralateral trunk lean at maximal ER has been associated with increased torque at the elbow1.  Addressing trunk muscle imbalances and faulty pitching mechanics at the trunk are important considerations for pitchers of all ages.

Throwing curveballs have long been controversial in youth baseball circles.  Lyman et al.2 found the curveball was associated with a 52% increased risk of shoulder pain and the slider was associated with an 86% increased risk of elbow pain in youth baseball players.  However, this systematic review showed no association between throwing breaking pitches and increased biomechanical stresses at the shoulder or elbow in youth baseball players. Little League Baseball currently recommends youth baseball players should not throw curveballs until the age of 14.  This corresponds to the period of peak growth for males.  Proper pitching mechanics and a love for the game should be emphasized during the baseball player’s youth playing days.  Mastering breaking pitches can easily be accomplished after the peak growth spurt without any detriment to the athlete’s long-term playing career.

As previously mentioned, proper pitching mechanics of the lower body and trunk are important to reduce arm stress and subsequent injury to the elbow and shoulder.  However, little research has been conducted on proper lower body and trunk pitching mechanics in youth baseball players.  A strong foundation in the lower body and trunk should be given the same attention as building arm strength.  Arm care exercise programs may achieve little performance or injury risk reduction without integrating the lower body and trunk.  Future studies investigating youth pitching biomechanics should include a greater analysis of the kinematics and kinetics of the entire kinetic chain and not just the upper extremity.

References

  1. Solomito MJ, Garibay EJ, Woods JR, Nissen CW. Lateral trunk lean in pitchers affects both ball velocity and upper extremity joint moments. Am J Sports Med. 2015;43(5):1235-1240. doi:10.1177/0363546515574060.
  2. Lyman S, Fleisig GS, Andrews JR, Osinski ED. Effect of pitch type, pitch count, and pitching mechanics on risk of elbow and shoulder pain in youth baseball pitchers. Am J Sports Med. 2002;30(4):463-468. http://www.ncbi.nlm.nih.gov/pubmed/12130397.

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