PURPOSE: The objective of this study was to examine the effect of vibration exercises generated from an XCO® trainer on supraspinatus, infraspinatus, teres minor, and deltoid muscle thickness. METHODS: Thirty subjects were evenly divided into two groups. Muscle thickness was measured by a sonogram prior to the study, and at three and six weeks after the intervention. Changes in muscle thickness were analyzed using a repeated measure analysis of variance (ANOVA). The significance level for the statistical test was set at α=0.05. RESULTS: A statistically significant differences in timing, interactions between timing and the groups, and between-group changes were demonstrated for supraspinatus muscle thickness (p < 0.05). A similar finding was reported for infraspinatus, teres minor, and deltoid muscles with regard to the interactions between timing and the groups (p < 0.05), although the between-group change did not reach statistical significance (p>0.05). CONCLUSION: Significant changes were observed in the thickness of the supraspinatus, infraspinatus, teres minor, and deltoid muscles, owing to the use of vibration exercises generated from an XCO® trainer. These findings can be used as a foundation for future studies on rehabilitation training.