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

Remote voluntary contraction, such as the classical Jendrassik maneuver (JM), is a procedure routinely used to increase the amplitude of tendon reflexes in the lower limb, In 8 healthy subjects we studied the effects of JM on the motor evoked potentials (MEP) recorded from tibialis anterior muscle, produced by transcranial magnetic stimulation (stimulus output of 5-10% over motor threshold), In this study, JM consisted here of a bilateral violent handgrip, preceding magnetic stimulation from 100 to 50 ms (steps of 100 ms), Compared to the control test, latencies remained unchanged, MEP amplitudes were greatly enhanced with a JM test interval from 200 to 400 ms (170% of control amplitude at 300 ms), We also studied 6 patients with severe alterations of MEPs from tibialis anterior muscle, In each case, JM preceding magnetic stimulation (stimulus output 100%) from 300 ms induced reappearance of response or marked enhancement of amplitude, allowing calculation of central 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 Wiley & Sons, Inc.