Context: Pitching injuries in youth baseball are increasing in incidence. Poor pitching mechanics in young throwers have not been sufficiently evaluated due to the lack of a basic biomechanical understanding of the "normal" youth pitching motion.
Objective: To provide a greater understanding of the kinetics and kinematics of the youth baseball pitching motion.
Data sources: PubMed, MEDLINE, and SPORTDiscus databases were searched from database inception through February 2017.
Study selection: A total of 10 biomechanical studies describing youth pitching mechanics were included.
Study design: Systematic review.
Level of evidence: Level 3.
Data extraction: Manual extraction and compilation of demographic, methodology, kinetic, and kinematic variables from the included studies were completed.
Results: In studies of healthy youth baseball pitchers, progressive external rotation of the shoulder occurs throughout the start of the pitching motion, reaching a maximum of 166° to 178.2°, before internally rotating throughout the remainder of the cycle, reaching a minimum of 13.2° to 17°. Elbow valgus torque reaches the highest level (18 ± 4 N·m) just prior to maximum shoulder external rotation and decreases throughout the remainder of the pitch cycle. Stride length is 66% to 85% of pitcher height. In comparison with a fastball, a curveball demonstrates less elbow varus torque (31.6 ± 15.3 vs 34.8 ± 15.4 N·m).
Conclusion: Multiple studies show that maximum elbow valgus torque occurs just prior to maximum shoulder external rotation. Forces on the elbow and shoulder are greater for the fastball than the curveball.
Keywords: biomechanics; curveball; fastball; pitching; youth baseball.