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

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.

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.

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.

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.