With regard to the research of isokinetic concentric and isometric strength, the quantities and qualities of literature in the previous thirty years were quite sufficient. However, the research on the analysis of isokinetic eccentric strength was still inadequate and far behind. The purpose of this study was to investigate the characteristics of shoulder rotators in elite tennis players, local tennis players, and healthy men. The main analysis focused on the examination of isokinetic concentric strength, isokinetic eccentric strength, and concentric strength ratios of shoulder external and internal rotators in order to identify the balance of strength of shoulder rotators. Thirty-six men (12 elite tennis players, 12 local tennis players and 12 healthy men) participated in this study. A Kin-Com isokinetic dynamometer was used to evaluate concentric and eccentric (angular velocities were 60, 120 and 180 deg/sec) strength of shoulder internal and external rotators. T-tests were used to compare dominant and non-dominant sides in three groups, respectively, and Oneway ANOVA tests were used to compare the differences of strength characteristics among three groups. Results showed that (a) there were significant differences in concentric and eccentric strength of internal rotators between dominant and non-dominant shoulders in three angular velocities at the elite and local tennis players; (b) there were not significant differences in concentric and eccentric strength of external rotators between dominant and non-dominant shoulders at three groups except concentric and eccentric strength of local players at 60 deg/sec; (c) there were not significant differences in concentric strength ratios of shoulder external and internal rotators among three groups, but the ratios in the non-dominant arm were greater than 1. The results of this study suggest that players need to notice the balance of strength of shoulder external and internal rotators in order to prevent or reduce the occurrence of shoulder injuries. In addition, the development of normative data may be applied in tennis training and clinical sports medicine.
