69 Australasian Physical & Engineering Sciences in Medicine Volume 27 Number 2, 2004 TECHNICAL NOTE Compensation of limb weight on interfaced raw torque signals from a KIN-COM ® dynamometer to an AMLAB ® Workstation S. Jaberzadeh 1 , H. Nazeran 2 , S. Scutter 3 and A. Warden-Flood 3 1 Discipline of Physiology and Research Centre for Human Movement Control, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, Australia 2 School of Informatics and Engineering, Flinders University, Adelaide, Australia 3 School of Physiotherapy, University of South Australia, Adelaide, Australia Abstract The effect of gravity should be considered when using isokinetic devices to measure human movement performance. In most isokinetic dynamometers gravity compensation is controlled by software through a gravity correction option. However in some complex research protocols the dynamometer signal acquisition and processing capability is not adequate to effectively synchronize or process a wide range of captured signals. Therefore when the force/torque signals from a commonly used dynamometer such as KIN-COM ® are interfaced into a signal processing workstation such as AMLAB ® , it is necessary to further process the received raw signals for gravity correction. The aim of this study was to evaluate the effectiveness of an AMLAB ® -based instrument designed for gravity compensation of raw torque signals acquired from a KIN-COM ® dynamometer. To check the accuracy of weight compensation within the AMLAB ® environment, torque signals produced by a known weight during a 180-degree range of KIN-COM ® lever arm movement were compared with and without weight compensation. The results indicated that this technique is an accurate means for weight compensation when raw torque signals from a KIN-COM ® dynamometer are interfaced to an AMLAB ® workstation. Key words weight correction, weight compensation Isokinetic dynamometry, KIN-COM ® dynamometer, AMLAB ® Introduction Isokinetic dynamometry is a widely used quantitative method for measurement of muscle performance in health and disease. The force or torque measurement of interest is that produced from muscle contraction. The weight of the limb segment produces a torque which is a source of error during force and torque measurements 1,2 . Therefore, in calculating the net muscle force during an isokinetic movement, the effect of the limb weight must be incorporated 2,3 . The importance of gravity correction during isokinetic dynamometry has been discussed by many authors 4-7 . Significant error is associated with isokinetic torque measurements not corrected for the effect of gravity 1,4,7 . Corresponding author: S. Jaberzadeh, Discipline of Physiology and Research Centre for Human Movement Control, School of Molecular and Biomedical Science, The University of Adelaide, Adelaide, SA 5005, Australia, Tel: 8 83036433, Fax: 8 83033356, Email: shapour.jaberzadeh@adelaide.edu.au Received: 29 October 2003; Accepted: 19 May 2004 Copyright © 2004 ACPSEM/EA This effect has been dramatically demonstrated for hamstring/quadriceps ratios 2,8,9 and situations where active torques are small 2,7 . There are few studies concerning method-related variations in estimates of gravity correction. Finucane et al 10 determined the error associated with the gravity-correction procedure of the KIN-COM ® dynamometer when a weight or limb segment was weighed at different lever arm positions. Most isokinetic dynamometers are controlled by sophisticated software that includes procedures for weight compensation through a gravity correction option. A robotic dynamometer such as KIN-COM  provides a system for control of angular velocity, recording range of movement and resistive torque signals, however in some complex research protocols 12 a multichannel EMG amplifier and a mechanism for reporting of pain are still required. Most dynamometers (e.g. KIN-COM ® ) are not designed to synchronize signals from a wide range of sources, and when such synchronization is required, integrated environments such as AMLAB ® or LAB-VIEW ® can be used. In our research, which investigates the effects of two different upper limb positions on mechanosensitivity of the median nerve 12 , it was necessary to interface the raw force/torque and ROM signals from the KIN-COM ® dynamometer to the AMLAB ® environment and therefore the gravity correction option by the dynamometer was bypassed.