THE EFFECT OF SOFTBALL BAT VIBRATION FREQUENCY ON ANNOYANCE RATINGS
AbstractINTRODUCTION The purpose of this study was to determine annoyance level associated with gripping a softball bat handle vibrating at different frequencies and intensities. Grip pressure at the point of maximum sensitivity and/or annoyance (GPRESMAX) was also estimated METHODS Twenty-six college males (n=13) and females (n= 13) ranging In age from 25 to 30 volunteered to participate. An eIectromechanical apparatus was used to excite the handle of an aluminium softball hat at the following frequencies while each subject grasped it with gradually increasing grip pressure: 100, 125. 160.200.250. 315, and 385 Hz. A plywood box covered the vibration apparatus to reduce ambient noise. Also, each subject wore ear plugs and ear muffs during the tests. Subjects placed their right hand on the vibrating rod with the first knuckle of the forefinger. wrist and elbow joints in alignment with the movement direction of the rod. The shaker provided two levels of excitation at 100 Hz (6 and 12 amps) and three levels of excitation (6, 12, and 18 amps) at each of the other frequencies. For each test, each subject grasped the vibrating rod with grip firmness gradually increasing from slight to maximum. After each condition, the subject rated the annoyance level on visual analogy scales 5 cm in length. RESULTS Annoyance was significantly related to both frequency and intensity increasing with increased intensity, and decreasing as the frequency increased. Post hoc group-by-group comparisons (least significant difference method) showed annoyance levels for 250. 315, and 385 Hz were significantly below those of all lower frequencies. Also, the annoyance level was highest at 160 and 200 Hz No relationship between subject sex and annoyance was loud. CONCLUSIONS Annoyance level was not related to subject sex, size, or grip strength. However, annoyance was highly and significantly related to both frequency and intensity of vibration, contributing to 23 and 20 per cent of the variability, respectively. These results indicate that hand-held implements with relatively higher fundamental frequencies are less annoying than those with lower fundamental frequencies
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