Before treating elbow injuries in the throwing athlete, the surgeon must understand the biomechanics of the elbow joint. Biomechanics is a function of kinematics, kinetics, and electromyography. Kinematics describes how something is moving without stating the causes behind the motion. Specifically, it quantifies linear and angular displacement, velocity, and acceleration—the effects of the motion. Elbow kinematics during throwing includes elbow flexion angles, angular velocities, and angular accelerations. High-speed videography or cinematography often is used to collect kinematic data.
Kinetics explains why an object moves the way it does; it quantifies both the forces and torques that cause the motion. Elbow kinetics includes the forces and torques about the elbow that cause elbow motion to occur. Inverse dynamics equations often are used in conjunction with kinematic and anthropometric data to estimate the net force or torque acting about the elbow.
Electromyography is used to quantify muscle activity. Surface electrodes often are used to detect muscle activity from larger surface muscles, and indwelling electrodes are used to detect muscle activity from smaller deep muscles.
In this chapter, we examine the biomechanics of the elbow, emphasizing the elbow of the throwing athlete. We discuss the overhand and underhand throwing motion, including the baseball pitch, the football pass, the tennis serve, the javelin throw, and the underhand softball pitch. The baseball pitching motion receives the most emphasis because most throwing-related studies have focused on this activity.
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Since World War II, there has been a tremendous change in the makeup and direction of kid baseball, as it is called. Adults, showing an unprecedented interest in the activity, have initiated and developed programs in thousands of towns across the United States programs that providebr wholesome recreation for millions of youngsters and are often a source of pride and joy to the community in which they exist.