Eccentric and concentric isokinetic knee flexion and extension: a reliability study using the Cybex 6000 dynamometer.

OBJECTIVE: To determine the reliability of the Cybex 6000 isokinetic dynamometer in measuring the knee muscle performance concentrically and eccentrically. METHODS: 18 male and 12 female subjects with no previous knee injuries, who had not previously undergone any isokinetic testing, were studied. The flexor and extensor muscles groups of both knees were tested at 60 degrees s-1 and 120 degrees s-1 with the continuous concentric-eccentric cycle testing protocol. Variables studied included peak torque, total work, and average power. The interclass correlation coefficient (ICC 2,1) was used to determine the reliability with P < 0.05. RESULTS: Peak torque showed significantly greater ICC than the total work and average power, with test-retest reliability ranging from 0.82 to 0.91 for peak torque, from 0.76 to 0.89 for total work, and 0.71 to 0.88 for average power. Average variability for the three variables studied ranged from 9% to 14%. The ICCs for the three variables studied were significantly greater at 120 degrees s-1. The knee extensor muscle group showed greater test-retest reliability, and the results of isokinetic testing in the concentric contraction mode were more reproducible. CONCLUSIONS: The Cybex 6000 isokinetic dynamometer shows high reliability in measuring isokinetic concentric and eccentric variables. Some fluctuation should be allowed when evaluating variations of muscle performance between tests.