The reliability of two different cybex isokinetic systems

The ability to accurately assess the strength of a variety of muscles is basic to professionals in a number of fields. The purposes of this study were to determine: 1) the intertest reliability of muscular strength utilizing two different Cybex II(R) isokinetic dynamometry systems and 2) reliability of peak torque values (PTV) obtained from two methods of data reduction [Cybex Data Reduction Computers (CDRC) and Cybex Strip Chart Recorders (SCR)]. Subjects (N = 50) were required to complete four knee extension/flexion cycles at two speeds (60 and 240 degrees /sec) on each of 2 test days which were separated by 1 day of rest. Correlation coefficients were used to determine the relationship between values obtained from two different Cybex systems and to determine the relationship of values obtained within each system from the CDRC and the SCR. ANOVA procedures were used to determine differences between values obtained using the two systems and between CDRC and SCR values obtained within a system. Correlation coefficients between CDRC and SCR PTVs indicated a strong relationship between values obtained within a system (r = 0.987 and r = 0.985 for Cybex A and B, respectively) and across systems (r = 0.983 and r = 0.982 for CDRC and SCR values, respectively). However, ANOVA results indicated that the Cybex II system (Cybex A) CDRC PTVs were higher (F = 5.64 and F = 23.90, p < 0.05 for extension and flexion, respectively) than those of the Cybex II+ system (Cybex B). No differences were noted between systems (F = 0.14 and F = 2.05, p > 0.05 for extension and flexion, respectively) for SCR PTVs. Clinicians should be aware that CDRC PTVs determined on different Cybex systems may not be comparable. However, SCR PTVs determined on different systems appear to be comparable. It should also be noted by clinicians that CDRCs and SCRs within the same system appear to be comparable. J Orthop Sports Phys Ther 1990;12(4):157-162.