A BASIC STUDY OF EXCITABILITY CHANGES IN HUMAN MOROR CORTEX AND MUSCLE FATIGUE

1999 Fiscal Year Final Research Report Summary

• Project/Area Number: 10680040
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 体育学
• Research Institution: KAGOSHIMA UNIVERSITY
• Principal Investigator: MARUYAMA Atsuo KAGOSHIMA UNIVERSITY, EDUCATION, ASSOCIATE PROFESSOR, 教育学部, 助教授 (80117548)
• Co-Investigator(Kenkyū-buntansha): ETOU Seiji KAGOSHIMA UNIVERSITY, MEDICINE, RESEARCH ASSOCIATE, 医学部, 助手 (70295244) ; KAWAHIRA Kazumi KAGOSHIMA UNIVERSITY, MEDICINE, ASSOCIATE PROFESSOR, 医学部, 助教授 (20117493) ; YUNOKUCHI Kazutomo KAGOSHIMA UNIVERSITY, ENGINEERING, PROFESSOR, 工学部, 教授 (10094187) ; TANAKA Nobuyuki KAGOSHIMA UNIVERSITY, MEDICINE, PROFESSOR, 医学部, 教授 (40041454)
• Project Period (FY): 1998 – 1999
• Keywords: MOTOR CORTEX / MUSCLE FATIGUE / MAXIMAM VOLUNTARY CONTRACTION AND SUBMAXIMAM COLUANTARY CONTRACTION / MOTOR EVKED POTENTIAL / SILENT PERIOD / IENEGRATED ELECTROMYOGRAM

Research Abstract

To define the function and measurement of excitability change in human motor cortex due to muscle fatigue, this propose was firstly to examine how differences in task conditions of muscle contraction change MEP and silent period responses elicited by transcraninal magnetic stimulation (TMS). Secondly how muscle fatigue induced by 100%MVC and 50%MVC influences the inhibitory and facilitatory responses in motor cortex by double TMSs and how single MEPs change during fatigue.
Two tasks conditions consist of 2-sec ramp method from 10 to 70%MVC and constant method for each 20 seconds task at four intensities of 20, 33, 46 and 60%MVC. Four MEP amplitudes by TMS increased according to four intensities of %MVC in constant method. But MEP amplitudes decreased while same %MVC intensities increased in 2-sec ramp method. The decline pattern of MEP by ramp method is suggested to have the function of additional excitability to the strength and speed controls in motor cortex and spinal system.
The method of only test stimulus, test+ISI 3ms conditioning stimuli and test +ISI 10 ms conditioning stimuli by double TMS is indicated to estimate the cortico-cortical inhibitory and facilitator responses in human motor cortex. Three MEPs amplitudes decreased more after than before muscle fatigue of l00%MVC. %MEP of 3ms decreased more but % MEP of l0ms increased more after than before fatigue. On the other hand, MEPs amplitudes also decreased more after than before 50%MVC. But %MEP of ISI 3ms increased more after than before muscle fatigue. After muscle fatigue the excitability increased only facilitation in Short l00%MVC but increased both inhibition and facilitation in long 50%MVC. During contraction in l00%MVC and 50%MVC, muscle strength and iEMG gradually decreased and Silent Period shortened with fatigue in both %MVC. MEP amplitude kept constant in 100%MVC but kept constant or progressively increased in 50%MVC.