Effects of Agonistic and Antagonistic Isometric Contraction on Motor Evoked Potentials in the Forearm

ABSTRACT

OBJECTIVE: To evaluate the effect of agonistic and antagonistic isometric contraction on the motor evoked potentials (MEP). METHOD: The MEP responses of right flexor carpi radialis (FCR) and extensor carpi radialis (ECR) muscles were simultaneously recorded during constant isometric flexion and extension of wrist. The intensities of isometric flexion and extension were 30%, 50%, and 100% of maximal voluntary contraction, which were achieved by isokinetic dynamometer. Background electromyographic activities in surface and needle electrodes were used for selective contraction. RESULTS: In agonistic muscles, the amplitudes of MEP responses were significantly increased according to the intensity of isometric contraction. In antagonistic muscles, the amplitudes of MEP responses in ECR were significantly increased with increasing intensity of isometric flexion. The amplitudes of MEP responses in FCR were increased with increasing intensity of isometric extension in spite of suppression in H-reflex of FCR during isometric extension. CONCLUSION: In antagonistic muscles, facilitation of MEP response in ECR and FCR during isometric contraction was occurred as in the agonistic isometric contraction.