Share this article on:

Influence of fatigue on EMG/force ratio and cocontraction in cycling

HAUTIER, CHRISTOPHE ANDRÉ; ARSAC, LAURENT MAURICE; DEGHDEGH, K.; SOUQUET, JIMMY; BELLI, ALAIN; LACOUR, JEAN-RENÉ

Medicine & Science in Sports & Exercise: April 2000 - Volume 32 - Issue 4 - p 839-843
Applied Sciences: Biodynamics

HAUTIER, C. A., L. M. ARSAC, K. DEGHDEGH, J. SOUQUET, A. BELLI, and J.-R. LACOUR. Influence of fatigue on EMG/force ratio and cocontraction in cycling. Med. Sci. Sports Exerc., Vol. 32, No. 4, pp. 839–843, 2000.

Purpose: The purpose of the present study was to observe force and power losses and electromyographic manifestations of fatigue during repeated sprints performed on a friction-loaded cycle ergometer.

Methods: Ten subjects performed 15 maximal 5-s sprints with 25-s rests between them. Power, velocity, and torque were measured during sprints 1 and 13 and during two submaximal constant-velocity (50 rpm) periods of cycling performed before and after the sprints. The EMG signals of five leg muscles were stored to determine the EMG/force ratio of power producer muscles and the coactivation of antagonist muscles. The power producer muscles were activated to the same level during sprints 1 and 13, despite a loss of force, whereas the vastus lateralis muscle was recruited more during the submaximal cycling period under fatigue conditions.

Results: This led to an increased EMG/force ratio for the power producer muscles, indicating the peripheral fatigue status of these muscles. Antagonist muscles were less activated during the sprints after fatigue; whereas they stayed unchanged during the last submaximal cycling period.

Conclusions: This suggests that there is a decrease in coactivation as agonist force is lost. This decrease in coactivation under fatigue conditions has not been previously reported and is probably due to the training status of the subjects. Subjects may have learned to better use their antagonist muscles to efficiently transfer force and power to the rotating pedal. This coordination can be adapted to cope with fatigue of the power producer muscles.

Laboratoire de Physiologie-GIP exercice, Faculté Médecine Lyon-Sud, BP 12, 69921 Oullins Cedex, FRANCE; Laboratoire d’Electronique, Mesure et Instrumentation-Université Lyon 1, FRANCE; Laboratoire des Sciences du Sport-UFR STAPS, Université de Franche-Comté, FRANCE; UFR STAPS-Université Blaise Pascal, B.P. 104, 63172 AUBIERE Cedex, FRANCE; and Faculté des Sciences du Sport et de L’Education Physique-Université Victor Segalen Bordeaux 2-Avenue Camille Jullian, 33405 TALENCE Cedex, FRANCE

Submitted for publication April 1998.

Accepted for publication June 1999.

Address for correspondence: Christophe André Hautier, Laboratoire de Physiologie-GIP exercice, Faculté Médecine Lyon-Sud, BP 12, 69921 Oullins Cedex, France. E-mail: hautier@cicsun.univ-bpclermont.fr.

© 2000 Lippincott Williams & Wilkins, Inc.