Tags

Type your tag names separated by a space and hit enter

Effects of fatigue on corticospinal excitability of the human knee extensors.
Exp Physiol. 2016 12 01; 101(12):1552-1564.EP

Abstract

NEW FINDINGS

What is the central question of this study? Do group III and IV muscle afferents act at the spinal or cortical level to affect the ability of the central nervous system to drive quadriceps muscles during fatiguing exercise? What is the main finding and its importance? The excitability of the motoneurone pool of vastus lateralis was unchanged by feedback from group III and IV muscle afferents. In contrast, feedback from these afferents may contribute to inhibition at the cortex. However, the excitability of the corticospinal pathway was not directly affected by feedback from these afferents. These findings are important for understanding neural processes during fatiguing exercise. In upper limb muscles, changes in afferent feedback, motoneurone excitability, and motor cortical output can contribute to failure of the central nervous system to recruit muscles fully during fatigue. It is not known whether similar changes occur with fatigue of muscles in the lower limb. We assessed the corticospinal pathway to vastus lateralis during fatiguing sustained maximal voluntary contractions (MVCs) of the knee extensors and during firing of fatigue-sensitive group III/IV muscle afferents maintained by postexercise ischaemia after fatiguing MVCs of the knee extensors and, separately, the flexors. In two experiments, subjects (n = 9) performed brief knee extensor MVCs before and after 2-min sustained MVCs of the knee extensors (experiment 1) or knee flexors (experiment 2). During MVCs, motor evoked potentials (MEPs) were elicited by transcranial magnetic stimulation over the motor cortex and thoracic motor evoked potentials (TMEPs) by electrical stimulation over the thoracic spine. During the 2-min extensor contraction, the size of vastus lateralis MEPs normalized to the maximal M-wave increased (P < 0.05), but normalized TMEPs were unchanged (P = 0.16). After the 2-min MVC, maintained firing of group III/IV muscle afferents had no effect on vastus lateralis MEPs or TMEPs (P = 0.18 and P = 0.50, respectively). Likewise, after the 2-min knee flexor MVC, maintained firing of these afferents showed no effect on vastus lateralis MEPs or TMEPs (P = 0.69 and P = 0.34, respectively). Motoneurones of vastus lateralis do not become less excitable during fatiguing isometric MVCs. Moreover, fatigue-sensitive group III/IV muscle afferents fail to affect the overall excitability of vastus lateralis motoneurones during MVCs.

Authors+Show Affiliations

Neuroscience Research Australia, Randwick, NSW, Australia. University of New South Wales, Kensington, NSW, Australia.Neuroscience Research Australia, Randwick, NSW, Australia. Centre for Heart, Lung and Vascular Health, School of Health & Exercise Sciences, University of British Columbia, Kelowna, BC, Canada.Neuroscience Research Australia, Randwick, NSW, Australia. University of New South Wales, Kensington, NSW, Australia.Neuroscience Research Australia, Randwick, NSW, Australia. University of New South Wales, Kensington, NSW, Australia.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

27652591

Citation

Kennedy, David S., et al. "Effects of Fatigue On Corticospinal Excitability of the Human Knee Extensors." Experimental Physiology, vol. 101, no. 12, 2016, pp. 1552-1564.
Kennedy DS, McNeil CJ, Gandevia SC, et al. Effects of fatigue on corticospinal excitability of the human knee extensors. Exp Physiol. 2016;101(12):1552-1564.
Kennedy, D. S., McNeil, C. J., Gandevia, S. C., & Taylor, J. L. (2016). Effects of fatigue on corticospinal excitability of the human knee extensors. Experimental Physiology, 101(12), 1552-1564. https://doi.org/10.1113/EP085753
Kennedy DS, et al. Effects of Fatigue On Corticospinal Excitability of the Human Knee Extensors. Exp Physiol. 2016 12 1;101(12):1552-1564. PubMed PMID: 27652591.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effects of fatigue on corticospinal excitability of the human knee extensors. AU - Kennedy,David S, AU - McNeil,Chris J, AU - Gandevia,Simon C, AU - Taylor,Janet L, Y1 - 2016/10/31/ PY - 2016/02/15/received PY - 2016/09/19/accepted PY - 2016/11/2/pubmed PY - 2018/1/3/medline PY - 2016/9/23/entrez KW - Group III and IV muscle afferents KW - corticospinal tract KW - muscle fatigue KW - transcranial stimulation SP - 1552 EP - 1564 JF - Experimental physiology JO - Exp Physiol VL - 101 IS - 12 N2 - NEW FINDINGS: What is the central question of this study? Do group III and IV muscle afferents act at the spinal or cortical level to affect the ability of the central nervous system to drive quadriceps muscles during fatiguing exercise? What is the main finding and its importance? The excitability of the motoneurone pool of vastus lateralis was unchanged by feedback from group III and IV muscle afferents. In contrast, feedback from these afferents may contribute to inhibition at the cortex. However, the excitability of the corticospinal pathway was not directly affected by feedback from these afferents. These findings are important for understanding neural processes during fatiguing exercise. In upper limb muscles, changes in afferent feedback, motoneurone excitability, and motor cortical output can contribute to failure of the central nervous system to recruit muscles fully during fatigue. It is not known whether similar changes occur with fatigue of muscles in the lower limb. We assessed the corticospinal pathway to vastus lateralis during fatiguing sustained maximal voluntary contractions (MVCs) of the knee extensors and during firing of fatigue-sensitive group III/IV muscle afferents maintained by postexercise ischaemia after fatiguing MVCs of the knee extensors and, separately, the flexors. In two experiments, subjects (n = 9) performed brief knee extensor MVCs before and after 2-min sustained MVCs of the knee extensors (experiment 1) or knee flexors (experiment 2). During MVCs, motor evoked potentials (MEPs) were elicited by transcranial magnetic stimulation over the motor cortex and thoracic motor evoked potentials (TMEPs) by electrical stimulation over the thoracic spine. During the 2-min extensor contraction, the size of vastus lateralis MEPs normalized to the maximal M-wave increased (P < 0.05), but normalized TMEPs were unchanged (P = 0.16). After the 2-min MVC, maintained firing of group III/IV muscle afferents had no effect on vastus lateralis MEPs or TMEPs (P = 0.18 and P = 0.50, respectively). Likewise, after the 2-min knee flexor MVC, maintained firing of these afferents showed no effect on vastus lateralis MEPs or TMEPs (P = 0.69 and P = 0.34, respectively). Motoneurones of vastus lateralis do not become less excitable during fatiguing isometric MVCs. Moreover, fatigue-sensitive group III/IV muscle afferents fail to affect the overall excitability of vastus lateralis motoneurones during MVCs. SN - 1469-445X UR - https://www.unboundmedicine.com/medline/citation/27652591/Effects_of_fatigue_on_corticospinal_excitability_of_the_human_knee_extensors_ L2 - https://doi.org/10.1113/EP085753 DB - PRIME DP - Unbound Medicine ER -