Inertial effects on moment curves and angle of peak moment during isokinetic knee extension

Abstract

The various isokinetic parameters are influenced by inertial moments developed during the acceleration and deceleration periods. Hence the purpose of this study was to examine inertial effects on moment versus angular displacement curves and on the angle of peak moment. Seven young adults performed 5 repetitions of concentric knee extension on the Lido isokinetic dynamometer at 30, 165 and 300 deg/s. The angular displacement and moment signals were collected and A/D converted via a 16 channel A/D card independently from the dynamometer software. Angular displacement data were smoothed using a second order Butterworth filter. The cut-off was approximately 5 Hz and was based on power spectrum assessment. Knee joint moment was calculated taking into account the inertial effects of the limb-lever arm system. Differences on the moment versus angular displacement curves were found before and after correction for the inertial effects.These differences were limited at medium to high velocities and during the initial and final parts of the movement. Angle of peak moment uncorrected and corrected for inertial effects decreased (closer to full extension) or increased (closer to full flexion) respectively as the velocity increased. It was concluded that erroneous moment curves and angle of peak moment are obtained at high velocities when the inertial effects are ignored. Therefore it is essential at high velocities to correct for inertial effects in order to obtain valid and comparable results and hence to achieve a more accurate approach to muscle and joint function assessment using these parameters.