Prerequisites and limitations to isokinetic measurements in humans - Investigations on a servomotor-controlled dynamometer

Physical and technical limitations have to be considered when measuring small torques over a wide range of angles during joint movements in humans using isokinetic methods, i.e. at constant angular velocities. In the concentric mode, during the initial phase, the subject must actively accelerate the lever of the isokinetic dynamometer to a preset velocity. To guarantee an adequate duration of the isokinetic phase at high preset velocities, greater torques are necessary to produce appropriate accelerations, otherwise the isokinetic phase will be increasingly shortened until the preset velocity can no longer be attained. The servomotor-controlled dynamometer used (LIDO-Active 2.1) continuously records torque during the whole movement, irrespective of differences between the actual and the preset velocity, but the user is not informed about which torques have been recorded outside the isokinetic phase and at which actual velocity. Thus, in the evaluation of torques in the nonisokinetic range, errors occur due to assigning torque measurements to incorrect velocities and due to the non-negligible accelerations involved. In exploratory tests on the dynamometer using physical methods to produce constant torques, an attempt has been made to ascertain the range over which isokinetic conditions were satisfied, hence providing a reliable basis for isokinetic studies in sports medicine and sports sciences.