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 the 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 retest session; to examine the reliability of the test. A concentric contraction of the dominant internal rotator was measured for peak torque, standardized peak torque, power, standardized power and acceleration time on a Cybex Norm isokinetic dynamometer under three conditions: 1) concentric contraction only, 2) isometric preload before a concentric contraction, and 3) eccentric preload before a concentric contraction.
RESULTS: Condition 3 showed a significant increase in peak torque production compared to condition 1 (p=0.001). Conditions 2 and 3 showed a significant 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 cycle in the internal rotator muscle group.