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 600 s5' and 1200 s51 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 significandy 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 1200 s-'. The concentric reliability, and Steiner et al,1 in subjects both with and without tibio-femoral pathology, reported moderate to excellent reliability in average peak torque (ICCs 0-58 to 0 96), total work (ICCs 0-63 to 0 93), and power (ICCs 0-67 to 0 93) for knee eccentric muscle performance.Recently, Frontera et al studied test-retest reliability of the knee extensor and flexor muscles in 178 45 to 78 year old subjects of both sexes using the Cybex II+ dynamometer.'9 They concluded that at least two tests should be performed to determine average peak torque accurately in older subjects.Bandy and McLaughlin'7 studied the intraand interdynamometer reliability of concentric muscle contraction using the Cybex II+ and the Cybex 6000, concluding that the two dynamometers were comparable when measuring concentric muscle contraction.In this study we determined the reliability of the Cybex 6000 isokinetic dynamometer by measuring knee flexor and extensor muscle performance both concentrically and eccentrically. MethodsThe knee flexor and extensor muscle groups of the dominant and non-dominant knee were tested in 18 males (age 27, SD 6-9 years) and 12 females (age 26, SD 5-8 years) (table 1) with no previous knee injury. Dominance was determined by asking the subjects to kick a ball placed in front of them. None of the subjects had previously undergone isokinetic testing.

Objective-To test the hypothesis that increasing the hamstrings and quadriceps (H:Q) isokinetic strength ratio will, in the short term, improve the functional ability of an anterior cruciate ligament (ACL) deficient knee.