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Effect of fatiguing maximal voluntary contraction on excitatory and inhibitory responses elicited by transcranial magnetic motor cortex stimulation
Author(s) -
McKay W. Barry,
Stokic Dobrivoje S.,
Sherwood Arthur M.,
Vrbova Gerta,
Dimitrijevic Milan R.
Publication year - 1996
Publication title -
muscle and nerve
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.025
H-Index - 145
eISSN - 1097-4598
pISSN - 0148-639X
DOI - 10.1002/mus.880190803
Subject(s) - transcranial magnetic stimulation , isometric exercise , excitatory postsynaptic potential , inhibitory postsynaptic potential , motor cortex , stimulation , silent period , contraction (grammar) , evoked potential , muscle contraction , electromyography , medicine , tibialis anterior muscle , psychology , physical medicine and rehabilitation , neuroscience , cardiology , skeletal muscle
Vertex transcranial magnetic stimulation (TMS) elicited tibialis anterior motor evoked potentials (MEPs) and silent periods (SPs) that were recorded during and following isometric maximal volitional contraction (MVC). During MVC in 6 healthy subjects, MEP amplitudes in the exercised muscle showed an increasing trend from an initial value of 4539 ± 809 μV (mean ± SE) to 550 ± 908 μV ( P < 0.13) while force and EMG decreased ( P < 0.01). Also, SP duration increased from 165 ± 37 ms to 231 ± 32 ms ( P < 0.01). Thus, during a fatiguing MVC both excitatory and inhibitory TMS‐induced responses increased. TMS delivered during repeated brief 10% MVC contractions before and after a fatiguing MVC in 5 subjects, showed no change in MEP amplitude but SP duration was prolonged after MVC. This SP prolongation was focal to the exercised muscle. Silent periods recorded after pyramidal tract stimulation were unchanged following the MVC. These results suggest that MEP and SP might have common sources of facilitation during an MVC and that inhibitory mechanisms remain focally augmented following a fatiguing MVC. © 1996 John Wiley & Sons, Inc.