URPOSE: To determine the patterns of electromyographic (EMG) responses and torques of upper extremity muscles in overhead throwers during maximal, eccentric muscle action for shoulder flexion (Flex_<Ecc>), abduction (Abd_<Ecc>) and diagonal activities (Dia_<Ecc>) with full glenohumeral internal rotation, at 60, 120, and 180°/s on the dynamometer. METHODS: Seven asymptomatic subjects (7 men, 4 women) who participate in overhead sports at least three days a week volunteered to participate in this study. Subjects were randomly performed with the test procedure which consisted of at least 5 grade maximal-effort repetitions on the three different testing conditions, at 60, 120, and 180°/s on the dynamometer, while we assessed muscle activation of the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and biceps brachii (BB) muscles by surface electromyography. EMG data was expressed as a percentage of maximum voluntary isometric contraction (%MVIC) that was obtained from the highest root mean square (RMS, 50ms) of each muscle and was normalized and averaged. RESULT: AD muscle elicited lower muscle activity during Dia_<Ecc> than Flex_<Ecc> and Abd_<Ecc>, (P<0.05) while the MD, PD, UT, MT, and LT muscles elicited overall greater muscle activities during Dia_<Ecc>. MD and MT muscle activities were significantly greater for the faster speed than for the slower speed as 60°/s during Abd_<Ecc>(P<0.05). Peak torque generated greater muscle strength for Dia_<Ecc> than Flex_<Ecc>, and Abd_<Ecc>, and it was significantly greater for the faster speed than slower speed during Dia_<Ecc> (P<0.05). CONCLUSION: Posterior upper extremity muscle activities and peak torque values were found to be dependent on eccentric muscle action for diagonal shoulder activity at the faster speed. This study provided evidence that isokinetic eccentric muscle strength testing of the posterior upper extremity muscle was effective to develop of a proper program for overhead sports athletes require forceful stability during deceleration phase.
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