METHOD-RELATED VARIATIONS IN ESTIMATES OF GRAVITY CORRECTION VALUES USING ELECTROMECHANICAL DYNAMOMETRY - A KNEE EXTENSION STUDY

Dynamometry is widely used to measure subject strength. The method emp loyed to correct dynamometry scores for gravitational influences can r esult in differing correction estimates. This study investigates diffe rences between mathematical estimates of correction values and directl y measured passive forces, Using the kin-Com dynamometer, passive forc e measurements from 90 degrees of knee flexion to full extension Here collected for nine asymptomatic subjects. These measurements were then compared with correction estimates mathematically extrapolated from a force reading obtained at one point in the test range. Direct passive measurements obtained between 0 and 70 degrees of knee flexion and ma thematical estimations of correction values differed by as much as 50 N. The equivalence of gravity correction values obtained using the two methods detailed cannot be assumed. Mathematical estimates of correct ion values for knee scores obtained between 0 and 90 degrees of flexio n were found to be clinically identical to direct passive measurements when : I) the limb was weighed close to 50 degrees of flexion and 2) the angular location of the lower limb mass relative to the horizontal was not assumed to be represented by the angular location oi the leve r arm, but rather 15 degrees further below the horizontal than the lev er arm.