Kinesiology, Vol. 36 No. 2., 2004.
Original scientific paper
Alterations of responses to transcranial magnetic stimulation during repeated isometric contractions
Nejc Šarabon
Abstract
Ten healthy male students (age 22.1+2.3 years), without neurological disorders, volunteered for the study. Muscle fatigue of the first dorsal interosseus muscle was studied during repeated isometric voluntary contractions until exhaustion. Transcranial magnetic stimulation was used to elicit motor-evoked potentials and mechanical responses in the exercised muscle. The averages of 6 responses were analyzed pre-exercise, every 25 contractions during the exercise and during the recovery phase. The average of isometric contractions until the fatiguing of a subject was 175 repetitions. During the protocol, amplitudes of mechanical as well as electrophysiological responses changed significantly (P<.001 and P<.002, respectively). A potentiation of the electrophysiological responses was prominent only at the beginning of the task while twitch force remained increased until the final fatiguing. Both measures were depressed after the task termination. However, diminishment of electromyographic responses remained more prominent. During the recovery phase twitch force fully recovered, while electrophysiological potentials remained depressed (P<.05). During and after the fatiguing task, modulations of mechanical and electrophysiological responses to transcranial magnetic stimulation were not parallel. Additional qualitative analysis of the electrophysiological responses revealed a systematic shift from biphasic responses in pre-tests to polyphasically shaped ones during the fatigue and recovery phase. This phenomenon could indicate a shift from monosynaptic to oligosynaptic corticospinal projections which could namely cause temporally different recruitment of the motor units. The modulatory mechanism is most probably of supraspinal origin while F wave as a measure of peripheral excitability did not show significant modifications through the experiment.
Keywords
central fatigue; brain stimulation; motor-evoked potentials; twitch
Hrčak ID:
4196
URI
Publication date:
23.12.2004.
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