Int J Sports Med 2005; 26(10): 847-853
DOI: 10.1055/s-2005-837459
Training & Testing

© Georg Thieme Verlag KG Stuttgart · New York

Central and Peripheral Fatigue of the Knee Extensor Muscles Induced by Electromyostimulation

R. Zory1 , 2 , D. Boërio1 , 3 , M. Jubeau1 , N. A. Maffiuletti1
  • 1INSERM/ERM 207 Motricité-Plasticité, Faculté des Sciences du Sport, Université de Bourgogne, Dijon, France
  • 2Laboratoire de Modélisation des Activités Sportives, Département STAPS de Chambéry, UFR CISM, Université de Savoie, Chambéry, France
  • 3Institut de Myologie, GH Pitié-Salpêtrière, Paris, France
Further Information

Publication History

Accepted after revision: November 20, 2004

Publication Date:
15 March 2005 (online)

Zoom Image

Abstract

The main purpose of this study was to characterise neuromuscular fatigue induced by 30 contractions of the knee extensor muscles evoked by electromyostimulation (EMS). Twelve healthy subjects were tested before and after a typical EMS session (frequency: 75 Hz, on-off ratio: 6.25 s on-20 s off) used for quadriceps femoris muscle strengthening. Surface electromyographic (EMG) activity and torque obtained during maximal voluntary and electrically evoked contractions were analysed to distinguish peripheral from central fatigue. Maximal voluntary torque of the knee extensor muscles decreased ∼ 20 % (p < 0.001) following EMS. In the same way, peak torque associated to single (p < 0.05) and paired (p < 0.001) stimuli as well as M-wave amplitude (p < 0.05) significantly decreased as a result of EMS. The raw EMG activity of both vastus lateralis and rectus femoris muscle recorded during maximal voluntary isometric contraction significantly decreased after the session (- 17.3 and - 14.5 %, respectively) whereas no changes were observed when EMG signals were normalised to respective M-wave amplitudes. Similarly, voluntary activation estimated by using the twitch interpolation technique was unchanged following EMS. In conclusion, a typical session of EMS of the knee extensor muscles mainly induced neuromuscular propagation failure while excitation-contraction coupling and neural mechanisms were not significantly affected. It is recommended to interpret surface EMG data together with the corresponding M wave, at least for the knee extensor muscles, in order to distinguish peripheral from central causes of fatigue.