Bat design and ball exit velocity in baseball: Implications for player safety
R.L. Nicholls* , B.C. Elliott & K. Miller
University of Western Australia
Table 1: Specifications of wood and metal baseball bats used in this study.
Empirical length- weight differential
Bat centre of Diameter mass at widest point of bat barrel (m) (balance point) (m)
Subjects: Informed consent was obtained from sixteen hitters from an Australian Baseball Federation summer baseball league. The subjects’ mean age was 22.81 4.58 years, height 1.77 0.74 m and mass 83.06 8.59 kg. A minimum batting average of .300 from the 1999-2000 season was required (mean .366 0.04). Ten subjects were right-handed, six were left-handed.
Data collection: All participants attended a familiarisation session at the indoor hitting facility prior to filming. Batting practice was undertaken with the test bats in a net-mesh batting tunnel (3 m x 4 m x 26 m). During data collection, experienced pitchers were used to pitch baseballs to each subject from a distance of 10.67 m. The mean pitch velocity was 20.47 m/s, corresponding to a speed of approximately 36 m/s over the regulation baseball pitching distance of 18.44 m, and representative of collegiate pitching speeds. Each subject hit with both wood and metal bats in a random order. Hitters were instructed to swing at pitches only in the mid-section of the strike zone, and practiced until they achieved a consistent pattern of linedrives directed toward centrefield. Each subject was subsequently filmed until producing five linedrives. Five to eight minutes recovery were permitted between use of each bat.
High-speed video data was collected using two electronically-synchronised 200 Hz cameras with a minimum shutter speed of 1/1000 s. Direct linear transformation was used to obtain three-dimensional (3D) coordinates for the motion of the bat and ball in time increments of 0.005 s. The global coordinate system to represent bat orientation in 3D space is illustrated in Figure 1, where the positive X-axis is directed toward the pitcher, positive Y is vertical, and positive Z is represented by the cross-product of the X and Y axes (out of the page).
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