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

This Article Full Text (PDF) 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 Gardiner, P F Articles by Olha, A E Search for Related Content PubMed PubMed Citation Articles by Gardiner, P F Articles by Olha, A E

Département d'éducation physique, Université de Montréal, Québec, Canada.

1. The ventral root dissection technique was used to obtain contractile and electromyogram (e.m.g.) characteristics of ninety-five plantaris motor units in situ in pentobarbitone-anaesthetized rats (n = 20). 2. Motor units demonstrated a wide spectrum of sizes, contractile speeds, and fatigue indices, and were categorized in the same manner as cat hind-limb motor units. Fast-fatigable (f.f.) and fast-intermediate fatigue resistant (f.i.) motor units constituted 20.2 and 25.5% of the motor unit population but together generated over 75% of the cumulative tetanic force. Fast-fatigue resistant (f.r.) and slow motor units composed 43.6 and 10.6% of the population while producing less than 25% of the aggregate tetanic force. 3. Only f.f. and a portion of f.i. motor units demonstrated extensive e.m.g. amplitude reductions during a standard fatigue test. Mean percentage e.m.g. decrease (from the first spike of the first burst to the last spike of the last burst) was 74.0 +/- 27.7% for f.f. units and 28.3 +/- 31.0% (mean +/- S.D.) for f.i. motor units. Relationships between percentage e.m.g. decline and motor unit size (tetanic force) showed significant (P less than 0.01) positive correlations in f.f. (r = 0.71) and f.i. (r = 0.69) motor units. 4. Backward extrapolation of the time course of the force-e.m.g. relationship during the fatigue test revealed that declines in e.m.g. may explain 15, 21 and 66% of the force losses in f.r., f.i. and f.f. motor units. Slow motor units were fatigue resistant and demonstrated a mean e.m.g. decline of 4.3 +/- 6.2%. 5. Indirectly stimulated whole muscle was more fatigable than a composite constructed from motor unit data because of more severe e.m.g. amplitude reductions in the former. 6. The motor unit mechanical and electrical responses during the fatigue test do not summate linearly during whole muscle contractile activity. This is most likely due to the presence, during whole muscle activity, of metabolic changes during the fatigue regimen which influence neuromuscular propagation of excitation, which are not as severe during single motor unit activity.

This article has been cited by other articles:

				D. C. Button, J. M. Kalmar, K. Gardiner, F. Cahill, and P. F. Gardiner Spike frequency adaptation of rat hindlimb motoneurons J Appl Physiol, March 1, 2007; 102(3): 1041 - 1050. [Abstract] [Full Text] [PDF]

				C. S. Klein, C. K. Hager-Ross, and C. K. Thomas Fatigue properties of human thenar motor units paralysed by chronic spinal cord injury J. Physiol., May 15, 2006; 573(1): 161 - 171. [Abstract] [Full Text] [PDF]

				C. K. Thomas, R. S. Johansson, and B. Bigland-Ritchie EMG Changes in Human Thenar Motor Units With Force Potentiation and Fatigue J Neurophysiol, March 1, 2006; 95(3): 1518 - 1526. [Abstract] [Full Text] [PDF]

				A. D. Karelis, M. Marcil, F. Peronnet, and P. F. Gardiner Effect of lactate infusion on M-wave characteristics and force in the rat plantaris muscle during repeated stimulation in situ J Appl Physiol, June 1, 2004; 96(6): 2133 - 2138. [Abstract] [Full Text] [PDF]

				A. D. Karelis, F. Peronnet, and P. F. Gardiner Insulin does not mediate the attenuation of fatigue associated with glucose infusion in rat plantaris muscle J Appl Physiol, July 1, 2003; 95(1): 330 - 335. [Abstract] [Full Text] [PDF]

				A. K. Wise, D. L. Morgan, J. E. Gregory, and U. Proske Fatigue in mammalian skeletal muscle stimulated under computer control J Appl Physiol, January 1, 2001; 90(1): 189 - 197. [Abstract] [Full Text] [PDF]

				A. J. Sokoloff Localization and Contractile Properties of Intrinsic Longitudinal Motor Units of the Rat Tongue J Neurophysiol, August 1, 2000; 84(2): 827 - 835. [Abstract] [Full Text] [PDF]

				T. G. Sutlive, J. R. McClung, and S. J. Goldberg Whole-Muscle and Motor-Unit Contractile Properties of the Styloglossus Muscle in Rat J Neurophysiol, August 1, 1999; 82(2): 584 - 592. [Abstract] [Full Text] [PDF]