Influence of the dynamometer driving mechanism on the isokinetic torque angle curve of knee extensors.

The purpose of this study was to assess the effect of the type of isokinetic driving mechanism on the torque angle curves of the knee extensors. Twenty healthy volunteers (11 male and 9 female) were tested alternately on an active and on a passive dynamometer. The active dynamometer (Quadriceps Dynamometer), provided with a starting threshold and a controlled acceleration, produced a curve with high torque readings in the first part of the range of motion. Subsequently a rather flat curve is found with a mean maximum torque of 158 N m at a joint position of 119° (angular velocity 90° s(-1)). The passive dynamometer (Cybex II) produced a curve with low torque readings in the initial phase and a mean maximum torque of 179 N m at a joint position of 123°. The maximum torque differences were statistically significant (P<0.05). It is concluded that the driving mechanism of the isokinetic device has a considerable influence on the initial phase of the torque angle curve and on the height of the maximum torque produced by the knee extensors.