Increases in corticospinal responsiveness during a sustained submaximal plantar flexion

• Published in: Journal of applied physiology (1985) 2009-07, Vol.107 (1), p.112-120
• Main Authors: Hoffman, B. W, Oya, T, Carroll, T. J, Cresswell, A. G
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Brain; Electric Stimulation - methods; Electromyography; Evoked Potentials, Motor - physiology; Fatigue; Female; Fundamental and applied biological sciences. Psychology; Humans; Isometric Contraction - physiology; Lower Extremity; Male; Motor ability; Motor Cortex - physiology; Muscle Fatigue - physiology; Muscle, Skeletal - physiology; Musculoskeletal system; Nervous system; Pyramidal Tracts - physiology; Studies; Transcranial Magnetic Stimulation - methods
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.91541.2008

1 School of Human Movement Studies and 3 School of Health and Rehabilitation Sciences, University of Queensland, Brisbane; and 2 School of Medical Sciences, Faculty of Medicine, University of New South Wales, Sydney, Australia Submitted 25 November 2008 ; accepted in final form 8 May 2009 Studying the responsiveness of specific central nervous system pathways to electrical or magnetic stimulation can provide important information regarding fatigue processes in the central nervous system. We investigated the changes in corticospinal responsiveness during a sustained submaximal contraction of the triceps surae. Comparisons were made between the size of motor-evoked potentials (MEPs) elicited by motor cortical stimulation and cervicomedullary motor-evoked potentials (CMEPs) elicited by magnetic stimulation of the descending tracts to determine the site of any change in corticospinal responsiveness. Participants maintained an isometric contraction of triceps surae at 30% of maximal voluntary contraction (MVC) for as long as possible on two occasions. Stimulation was applied to the motor cortex or the cervicomedullary junction at 1-min intervals during contraction until task failure. Peripheral nerve stimulation was also applied to evoke maximal M waves (M max ) and a superimposed twitch. Additionally, MEPs and CMEPs were evoked during brief contractions at 80%, 90%, and 100% of MVC as a nonfatigue control. During the sustained contractions, MEP amplitude increased significantly in soleus (113%) and medial gastrocnemius (108%) muscles and, at task failure, matched MEP amplitude in the prefatigue MVC ( 20–25% M max ). In contrast, CMEP amplitude increased significantly in medial gastrocnemius (51%), but not in soleus (63%) muscle and, at task failure, was significantly smaller than during prefatigue MVC (5–6% M max vs. 11–13% M max ). The data indicate that cortical processes contribute substantially to the increase in corticospinal responsiveness during sustained submaximal contraction of triceps surae. lower limb; central nervous system; muscle; transcranial magnetic stimulation; electromyogram Address for reprint requests and other correspondence: A. G. Cresswell, School of Human Movement Studies, Univ. of Queensland, QLD 4072, Australia (e-mail: a.cresswell{at}uq.edu.au )