Reliability of Absolute and Ratio Data In Assessment of Knee Extensor and Flexor Strength

The purpose of this investigation was to compare reliability coefficients and standard errors of measurement (SEM) for absolute (peak torque in newtonmeters) and ratio (concentric/eccentric (C/E)) and knee flexion/extension (KF/KE) ratios—as percentages) data. Forty healthy volunteers (20 men and 20 women) completed knee extension and flexion tests on two occasions within a 2-week period. On each occasion, two concentric and two eccentric muscle actions, with a 5-second rest between muscle actions, were completed from 90° to 5° flexion at 60 deg/sec angular velocity. For each gender, absolute scores were characterized by higher interrepetition, interoccasion, and overall intraclass correlation coefficients and lower relative measurement error (SEM/SD) than were either C/E or KF/KE ratios. These results do not discount the utility of ratio data, but suggest that to maximize reliability, ratio data should be acquired using more repetitions and/or occasions than is the case when using absolute data.