Context: The curveball is regarded by many as a potential risk factor for injury in youth baseball pitchers.
Objective: To critically evaluate the scientific evidence regarding the curveball and its impact on pitching biomechanics and the overall risk of arm injuries in baseball pitchers.
Study type: Systematic review.
Level of evidence: Level 3.
Data sources: Ovid MEDLINE from 1946 to 2012.
Study selection: Ten biomechanical studies on kinematic or electromyographic analysis of pitching a curveball were included, as well as 5 epidemiologic studies that assessed pain or injury incidence in pitchers throwing the curveball.
Data extraction: When possible, demographic, methodology, kinetics, and kinematics variables and pain/injury incidence were compiled.
Results: Two biomechanical studies found greater horizontal adduction of the shoulder at ball release and less shoulder internal torque during the curveball pitching motion. Two studies demonstrated less proximal force and less torque at the elbow as the arm accelerated when throwing a curveball compared with a fastball, as well as greater supination of the forearm and less wrist extension. Electromyographic data suggested increased activity of extensor and supinator muscles for curveballs. No studies found increased force or torque about the elbow or shoulder. Three epidemiologic studies showed no significant association between pitching a curveball and upper extremity pain or injury. One retrospective epidemiologic study reported a 52% increase in shoulder pain in pitchers throwing a curveball, although this may have been due to confounders.
Conclusion: Despite much debate in the baseball community about the curveball's safety in youth pitchers, limited biomechanical and most epidemiologic data do not indicate an increased risk of injury when compared with the fastball.
Keywords: baseball; curveball; pitching; throwing injuries.