HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 571/1/243    most recent jphysiol.2005.101600v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Prasartwuth, O. Articles by Taylor, J. L. Search for Related Content PubMed PubMed Citation Articles by Prasartwuth, O. Articles by Taylor, J. L. Related Collections Integrative

¹ Prince of Wales Medical Research Institute, University of New South Wales, Sydney, NSW, Australia
² School of Biomedical Sciences, Faculty of Health Sciences, The University of Sydney, Sydney, NSW, Australia
³ Department of Physiology, Monash University, Melbourne, Victoria, Australia

To assess the contribution of central and peripheral factors to changes in maximum voluntary force and its length dependence after eccentric muscle damage, voluntary and twitch torque were measured across a wide angular range, along with voluntary activation using twitch interpolation. Isometric torque from both maximum voluntary contractions (MVCs) and paired twitches to motor nerve stimulation were measured from 60 to 150 deg elbow flexion in 10 deg increments in eight subjects. Optimal angles were determined by curve fitting. Each subject then performed eccentric contractions until voluntary torque had decreased by 40%. Measurements were repeated at 2 h, 1 day and 8 days post-exercise to follow acute and longer-term changes. Before exercise, the optimal angle was in the mid-range (93 ± 10 deg; mean ±S.D.) for MVCs, and at a more extended elbow angle for the twitch (106 ± 6 deg, P < 0.05). Voluntary activation was generally high (> 94%) but depended on elbow angle, with activation being 4% lower at the most flexed compared to the most extended angle. Two hours after exercise, MVCs decreased 40%, while twitch torque declined 70%. All subjects showed a shift in optimal angle to longer muscle lengths for MVCs (17 ± 16 deg at 2 h, 14 ± 7 deg at day 1, P < 0.05). This shift contributed minimally (3%) to the reduction in torque at 90 deg, as the torque–angle relation was relatively flat around the optimum. The twitch showed a smaller shift (4 deg) to longer lengths which was not statistically significant. Voluntary activation was significantly impaired in the early stages after exercise (2 h and day 1, P < 0.05), particularly at short muscle lengths. By 8 days after exercise, the optimal angle had returned to pre-exercise values, but MVC, twitch torque and voluntary activation had not fully recovered. Eccentric exercise causes a short-term shift in the optimal angle for MVCs and produces a length-dependent impairment in voluntary activation. Therefore, it appears that both central and peripheral factors limit muscle performance following eccentric damage, with limits to voluntary drive being especially important at short lengths.

(Received 11 November 2005; accepted after revision 12 December 2005; first published online 15 December 2005)
Corresponding author S. Gandevia: Prince of Wales Medical Research Institute, University of New South Wales, Barker Street, Randwick, Sydney, NSW 2031, Australia. Email: s.gandevia{at}unsw.edu.au

This article has been cited by other articles:

				J. M. Dundon, J. Cirillo, and J. G. Semmler Low-frequency fatigue and neuromuscular performance after exercise-induced damage to elbow flexor muscles J Appl Physiol, October 1, 2008; 105(4): 1146 - 1155. [Abstract] [Full Text] [PDF]

				T. S. Turner, K. J. Tucker, N. C. Rogasch, and J. G. Semmler Impaired neuromuscular function during isometric, shortening, and lengthening contractions after exercise-induced damage to elbow flexor muscles J Appl Physiol, August 1, 2008; 105(2): 502 - 509. [Abstract] [Full Text] [PDF]

				D W Chapman, M J Newton, Z Zainuddin, P Sacco, and K Nosaka Work and peak torque during eccentric exercise do not predict changes in markers of muscle damage Br. J. Sports Med., July 1, 2008; 42(7): 585 - 591. [Abstract] [Full Text] [PDF]

				T. J. Dartnall, M. A. Nordstrom, and J. G. Semmler Motor Unit Synchronization Is Increased in Biceps Brachii After Exercise-Induced Damage to Elbow Flexor Muscles J Neurophysiol, February 1, 2008; 99(2): 1008 - 1019. [Abstract] [Full Text] [PDF]

				J. G. Semmler, K. J. Tucker, T. J. Allen, and U. Proske Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles J Appl Physiol, September 1, 2007; 103(3): 979 - 989. [Abstract] [Full Text] [PDF]