THE OCCURRENCE OF SYNKINESIS DURING KINESTHETIC POSITIONING RESPONSES.

Ten right dominant and ten left dominant male subjects were measured to determine the relationship of ipsilateral and contralateral muscular activity during active and passive positioning of the lower legs to specified angular positions. Accuracy of positioning was significantly influenced by the goal positions and by the mode of movement. The range of greatest accuracy occurred from full extension through 50 degrees of flexion. As the degree of flexion increased from 60 to 110 degrees, the errors of positioning also increased in magnitude. The direction of the error was influenced by the mode of movement. Although no statistically significant relationships were determined to occur between position accuracy and the amount of contralateral muscular activity as measured by the electromyogram, it was determined that this low intensity synkinesis does exist in the muscles of normal human subjects. Contrary to previous research, increased contralateral muscle activity occurred only during the passive limb movements and, more specifically, passive movements of the nondominant limbs. It was concluded that the dominant influence on accurate positioning of a leg was the indirect influence of muscles on the joint receptors. An increase in muscle activity was concluded to produce an increase distortion on the articular capsule and initiate a noise in the afferent channels which the sensory system was unable to filter. The synkinesis was interpreted to result from an attempt by the afferent system to mimic the noise normally produced by the muscular activity of the actively moved limb. Author