Skip to main content
NCBI home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1990 Feb;421:569–582. doi: 10.1113/jphysiol.1990.sp017962

Motor-unit force potentiation in adult cats during a standard fatigue test.

D A Gordon 1, R M Enoka 1, D G Stuart 1
PMCID: PMC1190102  PMID: 2348403

Abstract

1. The purpose of this study was to examine the time course of tetanic force during a standard fatigue test and to distinguish between the appearance of potentiation and fatigue among the four motor-unit types of a cat hindlimb muscle. 2. Motor units of the tibialis posterior muscle in the adult cat were assigned to four categories (i.e. types S, FR, FI, FF) based on conventional criteria (Burke, Levine, Tsairis & Zajac, 1973). The mean (+/- S.D.) time course of peak force was constructed for each motor-unit type and, within each type, for those units that potentiated (a greater than 3% increase in peak force compared to the initial value) and those that did not potentiate. 3. The average time courses of force differed between motor-unit types. There was, however, considerable variability within each motor-unit type. For the same relative force output, the forces exerted by slow-twitch units were less variable than those exerted by fast-twitch units. In addition, the variability among slow-twitch units was relatively constant during the fatigue test while variability among fast-twitch units either increased or decreased with time. 4. For a given motor-unit type, the average time course of force did not depend on whether force in each tetanus was expressed as a peak value, an average peak value, or a force-time integral. 5. Some motor units within each type exhibited potentiation. Most of the variability in the time course of the peak force for each motor-unit type could be accounted for by the potentiating units. Motor units that exhibited only force decline (i.e. fatigue), regardless of unit type, had less variable time courses of peak force. Since potentiation was transient in some unit types, it was assumed that at least two opposing processes (i.e. fatigue and potentiation) occurred simultaneously in these units (see also, Krarup, 1981; Rankin, Enoka, Volz & Stuart, 1988; Garner, Hicks & McComas, 1989). 6. It is concluded that the expression of force potentiation throughout a fatiguing regimen is variable among motor units and that this is not related to conventional motor-unit types. This dissociation suggests that the mechanisms that form the basis for the conventional distinction between motor-unit types are different from those which lead to force potentiation.

Full text

PDF
569

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Botterman B. R., Iwamoto G. A., Gonyea W. J. Classification of motor units in flexor carpi radialis muscle of the cat. J Neurophysiol. 1985 Sep;54(3):676–690. doi: 10.1152/jn.1985.54.3.676. [DOI] [PubMed] [Google Scholar]
  2. Burke R. E., Levine D. N., Tsairis P., Zajac F. E., 3rd Physiological types and histochemical profiles in motor units of the cat gastrocnemius. J Physiol. 1973 Nov;234(3):723–748. doi: 10.1113/jphysiol.1973.sp010369. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Burke R. E., Rudomin P., Zajac F. E., 3rd The effect of activation history on tension production by individual muscle units. Brain Res. 1976 Jun 18;109(3):515–529. doi: 10.1016/0006-8993(76)90031-7. [DOI] [PubMed] [Google Scholar]
  4. Close R., Hoh J. F. The after-effects of repetitive stimulation on the isometric twitch contraction of rat fast skeletal muscle. J Physiol. 1968 Jul;197(2):461–477. doi: 10.1113/jphysiol.1968.sp008570. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Dubose L., Schelhorn T. B., Clamann H. P. Changes in contractile speed of cat motor units during activity. Muscle Nerve. 1987 Oct;10(8):744–752. doi: 10.1002/mus.880100811. [DOI] [PubMed] [Google Scholar]
  6. Gardiner P. F., Olha A. E. Contractile and electromyographic characteristics of rat plantaris motor unit types during fatigue in situ. J Physiol. 1987 Apr;385:13–34. doi: 10.1113/jphysiol.1987.sp016481. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Garner S. H., Hicks A. L., McComas A. J. Prolongation of twitch potentiating mechanism throughout muscle fatigue and recovery. Exp Neurol. 1989 Mar;103(3):277–281. doi: 10.1016/0014-4886(89)90051-4. [DOI] [PubMed] [Google Scholar]
  8. Gordon D. A., Hamm T. M., Enoka R. M., Reinking R. M., Windhorst U., Stuart D. G. Measurement of axonal conduction velocity in single mammalian motor axons. J Neurosci Methods. 1987 Apr;19(4):267–284. doi: 10.1016/0165-0270(87)90070-7. [DOI] [PubMed] [Google Scholar]
  9. Hamm T. M., Nemeth P. M., Solanki L., Gordon D. A., Reinking R. M., Stuart D. G. Association between biochemical and physiological properties in single motor units. Muscle Nerve. 1988 Mar;11(3):245–254. doi: 10.1002/mus.880110309. [DOI] [PubMed] [Google Scholar]
  10. Jami L., Murthy K. S., Petit J., Zytnicki D. After-effects of repetitive stimulation at low frequency on fast-contracting motor units of cat muscle. J Physiol. 1983 Jul;340:129–143. doi: 10.1113/jphysiol.1983.sp014754. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Kernell D., Eerbeek O., Verhey B. A. Motor unit categorization on basis of contractile properties: an experimental analysis of the composition of the cat's m. peroneus longus. Exp Brain Res. 1983;50(2-3):211–219. doi: 10.1007/BF00239185. [DOI] [PubMed] [Google Scholar]
  12. Krarup C. Enhancement and diminution of mechanical tension evoked by staircase and by tetanus in rat muscle. J Physiol. 1981 Feb;311:355–372. doi: 10.1113/jphysiol.1981.sp013589. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. McDonagh J. C., Binder M. D., Reinking R. M., Stuart D. G. Tetrapartite classification of motor units of cat tibialis posterior. J Neurophysiol. 1980 Oct;44(4):696–712. doi: 10.1152/jn.1980.44.4.696. [DOI] [PubMed] [Google Scholar]
  14. Olson C. B., Swett C. P., Jr Effect of prior activity on properties of different types of motor units. J Neurophysiol. 1971 Jan;34(1):1–16. doi: 10.1152/jn.1971.34.1.1. [DOI] [PubMed] [Google Scholar]
  15. Rankin L. L., Enoka R. M., Volz K. A., Stuart D. G. Coexistence of twitch potentiation and tetanic force decline in rat hindlimb muscle. J Appl Physiol (1985) 1988 Dec;65(6):2687–2695. doi: 10.1152/jappl.1988.65.6.2687. [DOI] [PubMed] [Google Scholar]

Articles from The Journal of Physiology are provided here courtesy of The Physiological Society

RESOURCES