Inertial effects on moment development during isokinetic concentric knee extension testing.

Abstract

Two group pre-test post-test design was used with 2 isokinetic dynamometers in a laboratory setting. To evaluate the inertial effects on moment measurements during the initial acceleration period of concentric isokinetic knee extension. Torque acceleration energy is a controversial measure of muscle "explosive power." Moments due to acceleration during the initial period of isokinetic movements have been ignored in the majority of isokinetic studies. These inertial effects were assessed at various angular velocities measuring the work production at the initial 0.125 second on a Biodex and a Lido dynamometer. Four women (age, 23.33 +/- 2.49 years) and 5 men (age, 26.00 +/- 2.63 years) were tested on Biodex. A different group of 9 men (age, 23.4 +/- 3.41 years, height, 1.77 +/- 1.02 meters, and mass, 74 +/- 8.26 kg) was tested on the Lido. Joint moment was calculated by including moments associated with the angular acceleration of the lower limb and the lever arm. Torque acceleration energy was significantly greater after correction for inertial effects compared with uncorrected measures at moderate (165 and 180 deg/s) and high velocities (300 deg/s) on both dynamometers. In cases where moment development in the initial 0.125 second of an isokinetic movement is measured, it would be better to use slow velocities where inertial effects are minimum. At high angular velocities inertial correction is essential to acquire valid moment measurements and conclusions about muscle and joint function.