Effect of antagonistic voluntary contraction on motor responses in the forearm.
OBJECTIVE
We investigated the effects of voluntary contraction of agonist and antagonist muscles on motor evoked potentials (MEP) and on myoelectric activities in the target (agonist) muscle following transcranial magnetic stimulation (TMS).


METHODS
The left extensor carpi radialis (ECR) and flexor carpi radialis (FCR) muscles were studied in 16 healthy subjects. H reflexes, MEP induced by TMS, and background electromyographic (EMG) activity were recorded using surface electrodes at rest and during voluntary contraction of either agonist or antagonist muscles.


RESULTS
Voluntary contraction of antagonist muscles (at 10% of maximum contraction) enhanced the amplitudes of MEP for both muscles. The H reflex of the FCR muscle was inhibited by contraction (10% of maximum) of the ECR muscle. Background EMG activity did not differ between H-reflex trials and TMS trials. Enhancement of MEP amplitudes and background EMG activity during voluntary antagonist contraction was comparable in the two muscles. Appearance rate of MEP recorded by needle electrodes in response to subthreshold TMS was increased by antagonistic voluntary contraction.


CONCLUSIONS
Facilitation occurs during voluntary contraction of antagonist muscles. Differences between the effects of voluntary contraction of the ECR muscle for the MEP and the H reflex of the FCR suggest that cortical facilitatory spread occurs between agonist and antagonist muscles.
Izumi
S
S
Department of Rehabilitation Medicine, Tokai University School of Medicine, Boseidai, Isehara, 259-1193, Kanagawa, Japan. izumi@is.icc.u-tokai.ac.jp
Koyama
Y
Y
Furukawa
T
T
Ishida
A
A
D000328:Adult; D004576:Electromyography; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D005542:Forearm / Q000294:innervation*; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008280:Magnetics; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation*; D012016:Reference Values; D015203:Reproducibility of Results