Correction of isokinetic and isometric torque recordings for the effects of gravity. A clinical report.

The effect of gravity on neuromuscular perform­ ance should be measured in most research applica­ tions and in some clinical assessments. Comparing recorded values of maximal torque generated by knee extensor and flexor muscles using the Cybex® II* isokinetic dynamometer shows that gravity signifi­ cantly affects the recordings, resulting in an overestimation of active flexor muscle torque and an under­ estimation of active extensor muscle torque. 2 During both endurance and high velocity testing, the relative contribution of gravity to recorded torque values becomes increasingly large as active torque genera­ tion decreases. 2 The Cybex® II dynamometer with dual channel recorder allows one to record and measure isometric and isokinetic torque and also the specific joint angle at which the torque is produced. One of the advan­ tages of such a system is that the effect of gravity on measured torque may be calculated. In conducting our research, however, we encountered several diffi­ culties with the formula for gravity correction pro­ vided by Lumex, Inc. For instance, when using this formula, we did not obtain the anticipated zero effect of gravity when the force arm was vertical. Also, the mathematical derivation of this formula did not seem fully explained and therefore was unclear to us. Win­ ter et al devised a technique for correcting torque recordings for the effects of gravity. In order to use their technique, however, sophisticated equipment such as an accelerometer is required. In view of the disadvantages of these methods we derived what we consider to be an accurate and clinically feasible technique to compensate for the effect of gravity on the torque produced by muscle groups that are either facilitated or opposed by gravitational forces.