RELIABILITY OF DYNAMIC AND ISOMETRIC TESTING OF SHOULDER EXTERNAL ANDINTERNAL ROTATORS

Advances in isokinetic technology allow the physical therapist to asse ss concentric, eccentric, and isometric muscle performance at the shou lder in various positions. Research is limited, however, on the reliab ility of isokinetic measurements. The purposes of this study were: 1) to determine the test-retest reliability of concentric, eccentric, and isometric muscle performance measurements of shoulder external and in ternal rotation in the scapular plane test position and 2) to compare this reliability between the involved and uninvolved limb of subjects with a history of unilateral shoulder pathology. Fourteen males and 10 females (17-58 years) were tested on two occasions at 1-week interval s with the Biodex isokinetic dynamometer. Peak torque, total work, and average power were recorded for concentric tests at angular velocitie s of 60 and 120-degrees/sec and for eccentric tests at 60-degrees/sec. Maximum average isometric torque was recorded in two positions. Means , standard deviations, and mean differences between sessions with 95% confidence intervals were calculated. Intraclass correlation coefficie nts (ICCs) were used to determine test-retest reliability. Isometric t ests were generally most reliable (ICC = .81-.93), followed by concent ric (ICC = .60-.95) and eccentric tests (ICC = .44-.92). Isokinetic an d isometric reliability were usually higher for involved than uninvolv ed shoulders. The implication of these findings is that there appears to be greater variability with eccentric than concentric or isometric testing of shoulder rotation. Factors that possibly contributed to var iability are discussed. Clinicians should recognize potential sources of testing error when obtaining isokinetic measurements for use in cli nical decision-making. Further refinement of isokinetic testing protoc ols at the shoulder is recommended.