The stretch-shortening cycle of the internal rotators muscle group measured by isokinetic dynamometry

Background. The ability to measure the stretch-shortening cycle of isolated muscle groups has been limited. The purpose of this study was to measure t he stretch-shortening cycle of the internal rotator muscle group. Methods. Sixty-eight volunteer subjects, 35 men and 33 women, participated in one test session; eight men and eight women also participated in a retes t session; to examine the reliability of the test. A concentric contraction of the dominant internal rotator was measured for peak torque, standardize d peak torque, power, standardized power and acceleration time on a Cybex N orm isokinetic dynamometer under three conditions: 1) concentric contractio n only, 2) isometric preload before a concentric contraction, and 3) eccent ric preload before a concentric contraction. Results. Condition 3 showed a significant increase in peak torque productio n compared to condition I (p=0.001). Conditions 2 and 3 showed a significan t increase in power production compared to condition 1 (p=0.0001, p=0.003). A significant difference was found in all three conditions between the men and women, with the men producing greatest peak torques and powers. Conclusions. The testing protocol was found to have high reliability. This testing protocol could be used to further study the stretch-shortening cycl e in the internal rotator muscle group.