Corticospinal contributions to lower limb muscle activity during cycling in humans

Sidhu, Simranjit K. and Hoffman, Ben ORCID: https://orcid.org/0000-0002-8408-6192 and Cresswell, Andrew G. and Carroll, Timothy J. (2012) Corticospinal contributions to lower limb muscle activity during cycling in humans. Journal of Neurophysiology, 107 (1). pp. 306-314. ISSN 0022-3077


Abstract

The purpose of the current study was to investigate corticospinal contributions to locomotor drive to leg muscles involved in cycling. We studied 1) if activation of inhibitory interneurons in the cortex via subthreshold transcranial magnetic stimulation (TMS) caused a suppression of EMG and 2) how the responses to stimulation of the motor cortex via TMS and cervicomedullary stimulation (CMS) were modulated across the lo- comotor cycle. TMS at intensities subthreshold for activation of the corticospinal tract elicited suppression of EMG for approximately one-half of the subjects and muscles during cycling, and in matched static contractions in vastus lateralis. There was also significant modulation in the size of motor-evoked potentials (MEPs) elicited by TMS across the locomotor cycle (P ⬍ 0.001) that was strongly related to variation in background EMG in all muscles (r ⬎ 0.86; P ⬍ 0.05). When MEP and CMEP amplitudes were normalized to background EMG, they were relatively larger prior to the main EMG burst and smaller when background EMG was maximum. Since the pattern of modulation of normalized MEP and CMEP responses was similar, the data suggest that phase-dependent modulation of corticospinal re- sponses during cycling in humans is driven mainly by spinal mech- anisms. However, there were subtle differences in the degree to which normalized MEP and CMEP responses were facilitated prior to EMG burst, which might reflect small increases in cortical excitability prior to maximum muscle activation. The data demonstrate that the motor cortex contributes actively to locomotor drive, and that spinal factors dominate phase-dependent modulation of corticospinal excitability during cycling in humans.
transcranial


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Permanent restricted access to Published version in accordance with the copyright policy of the publisher.
Faculty/School / Institute/Centre: No Faculty
Faculty/School / Institute/Centre: No Faculty
Date Deposited: 03 Sep 2021 05:08
Last Modified: 03 Sep 2021 05:08
Uncontrolled Keywords: transcranial magnetic stimulation; knee extensors; electromyography
Fields of Research (2008): 11 Medical and Health Sciences > 1106 Human Movement and Sports Science > 110603 Motor Control
Fields of Research (2020): 42 HEALTH SCIENCES > 4207 Sports science and exercise > 420703 Motor control
Identification Number or DOI: https://doi.org/10.1152/jn.00212.2011
URI: http://eprints.usq.edu.au/id/eprint/42107

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