| Summary: | The purposes of this study were to; 1) investigate ball diameter as a control parameter by systematically adjusting the ratio of ball diameter and hand length; 2) determine any differences in pattern change relative to skill level of the thrower; and 3) determine critical values for change in pattern. Forty university students served as participants for this study. The average hand length was 18.74 cm with a standard deviation of 0.64 cm. Participants threw 10 times at 50% of maximum velocity. There was no requirement for accuracy. Segmental lag was digitized from trajectory graphs of segmental velocity. For data collection, participants threw balls of six different diameters. The only augmented information that was provided participants was whether velocity of throw was good or if they needed to slow down or speed up. Participants were able to maintain a 50% throwing velocity successfully during collection of data. A Level X Condition (3x6) MANOVA was performed on the dependent measures of segmental lag and velocity difference (humerus, forearm, hand). Coefficients of variation for segmental lag served to identify possible critical values by determining pattern variability. Three-dimensional scatterplots were used to help visualize pattern variation and stability of segmental lag within a movement space. Results of this study indicate that increasing the ratio of ball diameter to hand length is a control parameter that changes throwing patterns. The data indicate that when the ratio of hand length to ball diameter reached .74 throwing patterns changed. The lack of significance for coefficients of variance indicated that a critical value was not supported. Changes in pattern were best defined by changes in the relative position of forearm lag irrespective of level and condition. A change in humeral lag was important only to those throwers that took full advantage of the open kinetic chain. Hand lag remained generally constant across conditions and levels. In fact, only the most mature throwers exhibited a change from positive to negative lag with an increase in hand to ball diameter ratio. Increasing the hand to ball ratio changes the throwing pattern at a ratio between .86 and .74. When change occurs throwers are still attempting to take advantage of the open kinetic chain by maintaining as much distal lag as possible. The lag that is sacrificed most often is positive lag between the forearm and humerus. On a practical basis, care should be taken to insure that the size of the ball is appropriate for the throwers hand if positive change in throwing pattern is the goal of practice.
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