Isokinetic and electromyographic study of internal and external rotator muscles of tennis player

Abstract

The purpose of this study was to explore the effects of intensive tennis practice on the mechanical and electromyographic (EMG) activity of the external (ER) and internal (IR) rotators of the shoulder. Isokinetic and EMG testing of tennis (T, N = 8) and control (C, N = 8) subjects was performed using a CYBEX NORM. Shoulder rotation strength was measured at 5 angular velocities: concentric 60, 180, 300 and eccentric 60 and 180 ◦ /s during which peak torque (PT) and EMG activity of the infraspinatus (ER) and pectoralis major (IR) was recorded. For the T group dominant side (DS) the ER/IR ratio was lower than the non dominant side (NDS) whereas no such difference was observed between DS and NDS of C group. No ERecc/IRcon ratio difference was observed between sides and groups. ER co-activation in the T group was greater in the DS compared to the NDS and the DS of C group, while values were the same for both sides of C group. It therefore seems that tennis players present an adaptation to their activity. However their mechanical and EMG values deviate quite sharply from standard values which may potentially account for injury.