Closed-Loop Feedback Control in Skilled Overarm Throwers
Type of Degreedissertation
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Purpose: This investigation sought to determine whether skilled throwers can control the trajectory of overarm throws online following stride-foot contact. If online control is possible, the secondary purpose was to identify the sources of adjustment within the movement pattern. Method: Eight healthy, college-aged males with previous high school pitching experience and able to throw in excess of 31.3 m/s participated. Pretesting and testing took place in a motion capture laboratory. During the pretest, subjects performed 10 maximal-effort overarm throws with a tennis ball to a target 8.84 m away and 1.22 m above ground. Motion capture, EMG, ball speed, and ball landing location data were collected. Subjects returned within 48 hours for testing and performed 10 maximal-effort overarm throws in each of three experimental conditions where the target remained at its starting location (test-center) or translated 152.4 cm to the left (test-left) or right (test-right) upon stride-foot contact. Motion capture, EMG, ball speed, and ball landing location data were collected. Results: No significant differences (p > .05) were found between conditions in positional, velocity, or temporal kinematic parameters, as well as EMG parameters. Significant differences were found in ball trajectory parameters. The ball’s global landing location within the horizontal dimension in the test-left and test-right conditions was more negative and positive, respectively, than in the pretest and test-center condition. Radial error was higher in the test-left and test-right conditions than in the pretest; radial error in the test-right condition was also higher than in the test-center condition. Similarly, bivariate variable error was higher in the test-left and test-right conditions than in the pretest; bivariate variable error in the test-right condition was also higher than in the test-center condition. Ball speed was faster in the pretest than in all test conditions. Conclusion: Overall, these findings suggest that skilled throwers are able to control the trajectory of overarm throws online following stride-foot contact. The lack of differences in kinematic and EMG parameters was attributed to a combination of factors including task novelty, as well as intra-subject and inter-subject variations in the strategy adopted to make online adjustments.