HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 95/6/3512    most recent 01230.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Martin, P. G. Articles by Taylor, J. L. Search for Related Content PubMed PubMed Citation Articles by Martin, P. G. Articles by Taylor, J. L.

Output of Human Motoneuron Pools to Corticospinal Inputs During Voluntary Contractions

Prince of Wales Medical Research Institute and the University of New South Wales, Sydney, Australia

Submitted 23 November 2005; accepted in final form 7 February 2006

This study investigated transmission of corticospinal output through motoneurons over a wide range of voluntary contraction strengths in humans. During voluntary contraction of biceps brachii, motor evoked potentials (MEPs) to transcranial magnetic stimulation of the motor cortex grow up to about 50% maximal force and then decrease. To determine whether the decrease reflects events at a cortical or spinal level, responses to stimulation of the cortex and corticospinal tract (cervicomedullary motor evoked potentials, CMEPs) as well as maximal M-waves (M_max) were recorded during strong contractions at 50 to 100% maximum. In biceps and brachioradialis, MEPs and CMEPs (normalized to M_max) evoked by strong stimuli decreased during strong elbow flexions. Responses were largest during contractions at 75% maximum and both potentials decreased by about 25% M_max during maximal efforts (P < 0.001). Reductions were smaller with weaker stimuli, but again similar for MEPs and CMEPs. Thus the reduction in MEPs during strong voluntary contractions can be accounted for by reduced responsiveness of the motoneuron pool to stimulation. During strong contractions of the first dorsal interosseous, a muscle that increases voluntary force largely by frequency modulation, MEPs declined more than in either elbow flexor muscle (35% M_max, P < 0.001). This suggests that motoneuron firing rates are important determinants of evoked output from the motoneuron pool. However, motor cortical output does not appear to be limited at high contraction strengths.

This article has been cited by other articles:

				P. G. Martin, A. L. Hudson, S. C. Gandevia, and J. L. Taylor Reproducible Measurement of Human Motoneuron Excitability With Magnetic Stimulation of the Corticospinal Tract J Neurophysiol, July 1, 2009; 102(1): 606 - 613. [Abstract] [Full Text] [PDF]

				B. W. Hoffman, T. Oya, T. J. Carroll, and A. G. Cresswell Increases in corticospinal responsiveness during a sustained submaximal plantar flexion J Appl Physiol, July 1, 2009; 107(1): 112 - 120. [Abstract] [Full Text] [PDF]

				M. Gruber, V. Linnamo, V. Strojnik, T. Rantalainen, and J. Avela Excitability at the Motoneuron Pool and Motor Cortex Is Specifically Modulated in Lengthening Compared to Isometric Contractions J Neurophysiol, April 1, 2009; 101(4): 2030 - 2040. [Abstract] [Full Text] [PDF]

				T. Oya, B. W. Hoffman, and A. G. Cresswell Corticospinal-evoked responses in lower limb muscles during voluntary contractions at varying strengths J Appl Physiol, November 1, 2008; 105(5): 1527 - 1532. [Abstract] [Full Text] [PDF]

				S. K. Hunter, G. Todd, J. E. Butler, S. C. Gandevia, and J. L. Taylor Recovery from supraspinal fatigue is slowed in old adults after fatiguing maximal isometric contractions J Appl Physiol, October 1, 2008; 105(4): 1199 - 1209. [Abstract] [Full Text] [PDF]

				P. G. Martin, J. E. Butler, S. C. Gandevia, and J. L. Taylor Noninvasive Stimulation of Human Corticospinal Axons Innervating Leg Muscles J Neurophysiol, August 1, 2008; 100(2): 1080 - 1086. [Abstract] [Full Text] [PDF]

				M. Klass, M. Levenez, R. M. Enoka, and J. Duchateau Spinal Mechanisms Contribute to Differences in the Time to Failure of Submaximal Fatiguing Contractions Performed With Different Loads J Neurophysiol, March 1, 2008; 99(3): 1096 - 1104. [Abstract] [Full Text] [PDF]

				W. Taube, C. Leukel, M. Schubert, M. Gruber, T. Rantalainen, and A. Gollhofer Differential Modulation of Spinal and Corticospinal Excitability During Drop Jumps J Neurophysiol, March 1, 2008; 99(3): 1243 - 1252. [Abstract] [Full Text] [PDF]

				P. G. Martin, N. Weerakkody, S. C. Gandevia, and J. L. Taylor Group III and IV muscle afferents differentially affect the motor cortex and motoneurones in humans J. Physiol., March 1, 2008; 586(5): 1277 - 1289. [Abstract] [Full Text] [PDF]

				M. Levenez, S. J. Garland, M. Klass, and J. Duchateau Cortical and Spinal Modulation of Antagonist Coactivation During a Submaximal Fatiguing Contraction in Humans J Neurophysiol, February 1, 2008; 99(2): 554 - 563. [Abstract] [Full Text] [PDF]

				J. L. Taylor and S. C. Gandevia A comparison of central aspects of fatigue in submaximal and maximal voluntary contractions J Appl Physiol, February 1, 2008; 104(2): 542 - 550. [Abstract] [Full Text] [PDF]