A THREE-DIMENSIONAL ANALYSIS OF THE WINDMILL STYLE OF SOFTBALL DELIVERY FOR FAST AND CHANGE-UP PITCHING
AbstractINTRODUCTION The purpose of this study was to investigate the windmill style of softball delivery for fast and change-up pitches by three groups of female players (middle school, high school, and collegiate). This investigation examined kinematic and kinetic characteristics of the upper extremity, factors that contributed to differences between the magnitude of ball velocity, and the force exerted against the ground during the pitching motion. METHODS The volunteers for this study were 18 right-handed highly skilled female pitchers. Each subject performed three trials of each style of pitch. The best performance by subject by style was selected for analysis. The subjects' pitches were recorded by two video cameras which operated with a 60 Hz field rate. This data was then reduced to 3D coordinates using the DLT method. RESULTS It was concluded that the mean time for the fast pitch, from stride foot takeoff from the force platform to the point of ball release, was less than for the change-up pitch. The major factors that contributed to ball velocity were flexion of the elbow, shoulder, and hip joints. A stride length above 90 percent of the subject's height did not contribute to increased ball velocity. The normalized maximum mean value of the vertical ground reaction force for both styles of pitching, among the three groups, differed little. The difference in ball velocity between the fast and change-up pitches for middle school subjects were small compared to differences noted in the other two groups. The resultant joint torque at the shoulder and elbow were greater in high school and college subjects than in middle school subjects. Also, high school and college subjects showed greater peak angular velocity of the pitching arm than middle school subjects. CONCLUSIONS The following conclusions were based on the results of this study. Within subject stride length should not vary substantially in delivering fast and change-up pitches. A stride length of 80 to 90 percent of subject height is recommended. Vertical ground reaction force may not contribute substantially to ball velocity. Rapid acceleration and deceleration of the pitching arm that were noted in the delivery has implications for strengthening both the elbow and shoulder flexors and extensors.
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