Reliability of isokinetic decay slope is superior to using fatigue indices for shoulder horizontal abduction

Reliable and valid measurements for shoulder muscular endurance should be available for clinical use. The posterior shoulder endurance test offers a potential clinical assessment, but its construct validity isn't available. Since a criterion measure of muscular endurance is not available, this study's purpose was to determine a reliable method for testing shoulder muscular endurance using an isokinetic dynamometer.

The test-retest reliability, standard error measurement, and minimal detectable change were calculated on four different paradigms to quantify muscular fatigue using two isokinetic speeds (60°sec^-1,180°sec^-1). Calculation paradigms included peak torque fatigue index (FI), average torque FI, area-under-the-curve FI, and peak torque decay slope. Testing occurred on two days. Repeated measures analysis of variance compared the two peak torque decay slopes across both testing days.

Superior reliability was found within the decay slope measurements at both 60°sec^-1 (ICC = 0.941) and 180°sec^-1 (ICC = 0.764) speeds, with the 60°sec^-1 decay slope being the highest reliability between the two angular velocities. There was a greater amount of fatigue in the 60°sec^-1 decay slope compared to the 180°sec^-1 decay slope.

Using the decay slope of isokinetic shoulder horizontal abduction at 60°sec^-1 is a reliable method to validate other muscular endurance clinical measures. Rehabilitation specialists should utilize the decay slope of the isokinetic dynamometry to monitor responsiveness.