Relationship between peak moment, power and work corrected for the influence of inertial effects

Abstract

Moment measurements in isokinetic dynamometry are influenced by moments due to acceleration. The purpose of the present study was to examine the inertial effects on peak moment, power and work during concentric isokinetic knee extension at 60, 180 and 300 deg/s. Seven healthy young adults participated in the present study. Angular displacement from the Biodex software was used to calculate angular velocity and acceleration. A recursive second-order Butterworth filter was applied on angular displacement data and a cut-off frequency of approximately 5 Hz was used based on power spectrum assessment. Finally the actual joint moment was calculated by taking into account the moments due to acceleration of the limb-lever arm system. In general the correlations between the examined parameters were not influenced by inertial effects. A weak relationship between peak moment and power was found at 300 deg/s. Furthermore the differences between dynamometer moment and the moment corrected for the inertial effects increased as the preselected angular velocity increased. At 300 deg/s the dynamometer moment was 8.12% higher than the calculated joint moment. Absolute values of work measurements were similar before and after correction but work production was different during the initial acceleration and the final deceleration periods. Based on our findings it was concluded that corrections for inertial effects are essential during moment, work and power measurements at high velocities in isokinetic dynamometry. Finally, work and power should not be replaced by peak moment because they depend on both the range of motion and the moment development throughout the range of motion and therefore offer additional information concerning muscle and joint function.