Skip to main content
PMC home page
The Journal of Physiology logoLink to The Journal of Physiology
. 1973 Apr;230(2):359–370. doi: 10.1113/jphysiol.1973.sp010192

The orderly recruitment of human motor units during voluntary isometric contractions

H S Milner-Brown, R B Stein, R Yemm
PMCID: PMC1350367  PMID: 4350770

Abstract

1. The contractile properties of human motor units from the first dorsal interosseus muscle of the hand were studied during voluntary isometric contractions using recently developed techniques.

2. The twitch tensions produced by motor units varied widely from about 0·1-10 g. The twitch tension of a motor unit varied nearly linearly as a function of the level of voluntary force at which it was recruited over the entire range of forces studied (0-2 kg).

3. The number of additional motor units recruited during a given increment in force declined sharply at high levels of voluntary force. This suggests that even though the high threshold units generate more tension, the contribution of recruitment to increases in voluntary force declines at higher force levels.

4. Contraction times for these motor units varied from 30 to 100 msec. Over 80% had contraction times less than 70 msec, and might be classed as fast twitch motor units. The larger motor units, which were recruited at higher threshold forces, tended to have shorter contraction times than the smaller units.

Full text

PDF
359

Selected References

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

  1. Ashworth B., Grimby L., Kugelberg E. Comparison of voluntary and reflex activation of motor units. Functional organization of motor neurones. J Neurol Neurosurg Psychiatry. 1967 Apr;30(2):91–98. doi: 10.1136/jnnp.30.2.91. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. BASMAJIAN J. V. Control and training of individual motor units. Science. 1963 Aug 2;141(3579):440–441. doi: 10.1126/science.141.3579.440. [DOI] [PubMed] [Google Scholar]
  3. Buchthal F., Schmalbruch H. Contraction times and fibre types in intact human muscle. Acta Physiol Scand. 1970 Aug;79(4):435–452. doi: 10.1111/j.1748-1716.1970.tb04744.x. [DOI] [PubMed] [Google Scholar]
  4. Burke R. E. Firing patterns of gastrocnemius motor units in the decerebrate cat. J Physiol. 1968 Jun;196(3):631–654. doi: 10.1113/jphysiol.1968.sp008527. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Burke R. E., Levine D. N., Zajac F. E., 3rd Mammalian motor units: physiological-histochemical correlation in three types in cat gastrocnemius. Science. 1971 Nov 12;174(4010):709–712. doi: 10.1126/science.174.4010.709. [DOI] [PubMed] [Google Scholar]
  6. Burke R. E. Motor unit types of cat triceps surae muscle. J Physiol. 1967 Nov;193(1):141–160. doi: 10.1113/jphysiol.1967.sp008348. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Close R. I. Dynamic properties of mammalian skeletal muscles. Physiol Rev. 1972 Jan;52(1):129–197. doi: 10.1152/physrev.1972.52.1.129. [DOI] [PubMed] [Google Scholar]
  8. ECCLES J. C., ECCLES R. M., LUNDBERG A. The action potentials of the alpha motoneurones supplying fast and slow muscles. J Physiol. 1958 Jul 14;142(2):275–291. doi: 10.1113/jphysiol.1958.sp006015. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. FEINSTEIN B., LINDEGARD B., NYMAN E., WOHLFART G. Morphologic studies of motor units in normal human muscles. Acta Anat (Basel) 1955;23(2):127–142. doi: 10.1159/000140989. [DOI] [PubMed] [Google Scholar]
  10. GRANIT R., PHILLIPS C. G., SKOGLUND S., STEG G. Differentiation of tonic from phasic alpha ventral horn cells by stretch, pinna and crossed extensor reflexes. J Neurophysiol. 1957 Sep;20(5):470–481. doi: 10.1152/jn.1957.20.5.470. [DOI] [PubMed] [Google Scholar]
  11. Grillner S., Udo M. Recruitment in the tonic stretch reflex. Acta Physiol Scand. 1971 Apr;81(4):571–573. doi: 10.1111/j.1748-1716.1971.tb04935.x. [DOI] [PubMed] [Google Scholar]
  12. Grimby L., Hannerz J. Differences in recruitment order of motor units in phasic and tonic flexion reflex in "spinal man". J Neurol Neurosurg Psychiatry. 1970 Oct;33(5):562–570. doi: 10.1136/jnnp.33.5.562. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Grimby L., Hannerz J. Recruitment order of motor units on voluntary contraction: changes induced by proprioceptive afferent activity. J Neurol Neurosurg Psychiatry. 1968 Dec;31(6):565–573. doi: 10.1136/jnnp.31.6.565. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. HENNEMAN E., SOMJEN G., CARPENTER D. O. FUNCTIONAL SIGNIFICANCE OF CELL SIZE IN SPINAL MOTONEURONS. J Neurophysiol. 1965 May;28:560–580. doi: 10.1152/jn.1965.28.3.560. [DOI] [PubMed] [Google Scholar]
  15. Kernell D. Input resistance, electrical excitability, and size of ventral horn cells in cat spinal cord. Science. 1966 Jun 17;152(3729):1637–1640. doi: 10.1126/science.152.3729.1637. [DOI] [PubMed] [Google Scholar]
  16. MCPHEDRAN A. M., WUERKER R. B., HENNEMAN E. PROPERTIES OF MOTOR UNITS IN A HETEROGENEOUS PALE MUSCLE (M. GASTROCNEMIUS) OF THE CAT. J Neurophysiol. 1965 Jan;28:85–99. doi: 10.1152/jn.1965.28.1.85. [DOI] [PubMed] [Google Scholar]
  17. MCPHEDRAN A. M., WUERKER R. B., HENNEMAN E. PROPERTIES OF MOTOR UNITS IN A HOMOGENEOUS RED MUSCLE (SOLEUS) OF THE CAT. J Neurophysiol. 1965 Jan;28:71–84. doi: 10.1152/jn.1965.28.1.71. [DOI] [PubMed] [Google Scholar]
  18. MERTON P. A. The silent period in a muscle of the human hand. J Physiol. 1951 Jun;114(1-2):183–198. doi: 10.1113/jphysiol.1951.sp004610. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Milner-Brown H. S., Stein R. B., Yemm R. Changes in firing rate of human motor units during linearly changing voluntary contractions. J Physiol. 1973 Apr;230(2):371–390. doi: 10.1113/jphysiol.1973.sp010193. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Milner-Brown H. S., Stein R. B., Yemm R. Mechanisms for increased force during voluntary contractions. J Physiol. 1972 Oct;226(2):18P–19P. [PubMed] [Google Scholar]
  21. Milner-Brown H. S., Stein R. B., Yemm R. The contractile properties of human motor units during voluntary isometric contractions. J Physiol. 1973 Jan;228(2):285–306. doi: 10.1113/jphysiol.1973.sp010087. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Olson C. B., Carpenter D. O., Henneman E. Orderly recruitment of muscle action potentials. Arch Neurol. 1968 Dec;19(6):591–597. doi: 10.1001/archneur.1968.00480060061008. [DOI] [PubMed] [Google Scholar]
  23. Sica R. E., McComas A. J. Fast and slow twitch units in a human muscle. J Neurol Neurosurg Psychiatry. 1971 Apr;34(2):113–120. doi: 10.1136/jnnp.34.2.113. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Stein R. B., French A. S., Mannard A., Yemm R. New methods for analysing motor function in man and animals. Brain Res. 1972 May 12;40(1):187–192. doi: 10.1016/0006-8993(72)90126-6. [DOI] [PubMed] [Google Scholar]
  25. Stephens J. A., Taylor A. Fatigue of maintained voluntary muscle contraction in man. J Physiol. 1972 Jan;220(1):1–18. doi: 10.1113/jphysiol.1972.sp009691. [DOI] [PMC free article] [PubMed] [Google Scholar]

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

RESOURCES