Kinematic and Kinetic Comparison of Overhand and Underhand Pitching: Implications to Proximal-to-Distal Sequencing

Abstract

Because the segments of the body are linked, the movement of one component affects the action of all the other components of that segment, suggesting that there is an interaction between segments in an open kinetic chain movement. Typically, these segments interact in a sequence from the segment that is most proximal to a segment that is most distal. This interaction is known as proximal-to-distal sequencing. This sequence results in a summation of speed at the most distal segment producing a maximal end segment velocity. Although there is no question that this principle occurs, the mechanism of this interaction is still under scrutiny. Currently there are two explanations for the proximal-to-distal sequence, both based on the principle of conservation of angular momentum. Theory One states that once the motion of the system begins, an angular momentum is developed in the system and the distal segment lags behind. As the proximal segment approaches maximum velocity, an external force opposes this motion, which negatively accelerates the proximal segment, allowing inertia to propel the distal segment forward. Theory Two contends that no external torque is applied to the system after the initial acceleration of the system takes place. The system, with some mass, is said to move with a given angular velocity, thus having an angular momentum, which is conserved throughout the action. In this theory, as the proximal segment reaches its maximum angular velocity, an internal muscle moment is applied between the proximal and distal segments to accelerate the distal segment. Currently there is a wealth of information on the kinetics and kinematics of the overhand baseball throw, but surprisingly little on the underhand softball pitch, which includes a flexion action. Even more surprising is that these two pitching motions have received no direct study to analyze the overhand motion in terms of proximal-to-distal sequencing compared to the somewhat analogous underhand pitch in softball. Furthermore, the agonist/antagonist activation of the primary musculature that would cause the desired joint action at the elbow (extensors in baseball, flexors in softball) has also been neglected in the literature. Using motion capture 3-D analysis, the results of this study confirmed the existence of proximal-to-distal sequencing in both throwing types and illustrated that both types can be theoretically categorized as Theory One, with inertial acceleration of the distal segment. Furthermore, the musculature acting at the elbow can be considered analogous in both types of pitches.