Effect of transient moment-oscillations on the reliability of isokinetic shoulder elevation in the scapular plane

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The reliability of gravity corrected average and peak isokinetic moment of the shoulder elevators in the scapular plane, was assessed in 22 male college students without shoulder or neck pathology. Measurements were performed on two occasions, 7 days apart, by the same examiner. Both dominant and non-dominant sides were examined at 60 and 120°.s -1 , using Kin Com II dynamometer. Each volunteer was assessed in the seated position, elevating the shoulder between 30-90° with the elbow in extension and the forearm in pronation. Reliability of both non-free and free of transient moment-oscillations (TMO) peak and average moment data (data selected from the entire range and the range of motion where isokinetic velocity was constant and equal to the pre-selected angular velocity, respectively) was determined using the intraclass correlation coefficient (ICC 3,1). The variability of isokinetic moment data associated with normal fluctuations of strength performance over repeated measurements (inter-session variability) was determined using the standard error of measurement (SEM) and the limits of agreement (LOA). The ICC (3,1) values ranged between 0.86-0.95. Inter-sessions variability of isokinetic moment data calculated using 95% SEM and 95% LOA were similar and ranged between 8.9-15.9 Nm. Both SEM and LOA revealed lower variability for average compared to peak moment data, non-free compared to free of TMO average moment and for free compared to non-free of TMO peak moment data. Higher ICC values and lower variability was also obtained for peak moment data at the isokinetic velocity of 60 compared to 120°.s -1 and for most of the moment data recorded on the dominant compared to the non-dominant side. The present findings suggest that strength changes observed over repeated isokinetic measurements of the shoulder elevators in the scapular plane, may be better identified under certain conditions but they should only be considered as significant changes if they are lower or greater than inter-session variability of isokinetic moment data.