title: Facilitation of motor evoked potentials: timing of Jendrassik maneuver effects.
abstract: 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.
mesh_terms: D000328:Adult; D004576:Electromyography; D004594:Electrophysiology; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006801:Humans; D007866:Leg; D008280:Magnetics; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000503:physiopathology; D009119:Muscle Contraction; D010812:Physical Stimulation; D012018:Reflex / Q000502:physiology*; D012600:Scoliosis / Q000503:physiopathology; D013119:Spinal Cord Injuries / Q000503:physiopathology; D013997:Time Factors