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Activation varies among the knee extensor muscles during a submaximal fatiguing contraction in the seated and supine postures

¹Institut National de la Santé et de la Recherche Médicale/Equipe de Recherche et d'Innovation Technologique 0207, Motricité-Plasticité, Unité de Formation et de Recherche Sciences et Techniques des Activités Physiques et Sportive, Université de Bourgogne, 21078 Dijon, France; and ²Department of Integrative Physiology University of Colorado at Boulder, Boulder, Colorado 80309-0354

Submitted 3 April 2003 ; accepted in final form 27 June 2003

Ten young men sustained an isometric contraction of the knee extensor muscles at 20% of the maximum voluntary contraction (MVC) torque on three separate occasions in a seated posture. Subjects performed an isometric knee extension contraction on a fourth occasion in a supine posture. The time to task failure for the seated posture was similar across sessions (291 ± 84 s; P > 0.05), and the MVC torque was similarly reduced across sessions after the fatiguing contraction (42 ± 12%). The rate of increase in electromyograph (EMG) activity (%MVC) and torque fluctuations during the fatiguing contractions were similar across sessions. However, the rate of increase in EMG differed among the knee extensor muscles: the rectus femoris began at a greater amplitude (31.5 ± 11.0%) compared with the vastus lateralis and vastus medialis muscles (18.8 ± 5.3%), but it ended at a similar value (45.4 ± 3.1%). The time to task failure and increase in EMG activity were similar for the seated and supine tasks; however, the reduction in MVC torque was greater for the seated posture. These findings indicate that the time to task failure for the knee extensor muscles that have a common tendon insertion did not alter over repeat sessions as had been observed for the elbow flexor muscles (Hunter SK and Enoka RM. J Appl Physiol 94: 108-118, 2003).

electromyograph; force fluctuations; task failure; muscle length

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