FACILITATION OF MOTOR EVOKED-POTENTIALS - TIMING OF JENDRASSIK MANEUVER EFFECTS

Remote voluntary contraction, such as the classical Jendrassik maneuve r (JM), is a procedure routinely used to increase the amplitude of ten don reflexes in the lower limb, In 8 healthy subjects we studied the e ffects of JM on the motor evoked potentials (MEP) recorded from tibial is anterior muscle, produced by transcranial magnetic stimulation (sti mulus output of 5-10% over motor threshold), In this study, JM consist ed here of a bilateral violent handgrip, preceding magnetic stimulatio n from 100 to 50 ms (steps of 100 ms), Compared to the control test, l atencies remained unchanged, MEP amplitudes were greatly enhanced with a JM test interval from 200 to 400 ms (170% of control amplitude at 3 00 ms), We also studied 6 patients with severe alterations of MEPs fro m tibialis anterior muscle, In each case, JM preceding magnetic stimul ation (stimulus output 100%) from 300 ms induced reappearance of respo nse or marked enhancement of amplitude, allowing calculation of centra l conduction time, Such a technique, which is easy to perform, may be useful in clinical practice to calculate central motor conduction time , where it would otherwise be difficult or impossible. (C) 1995 John W iley & Sons, Inc.