The relationship of motor unit size, firing rate and force

R. A. Conwit, D. Stashuk, B. Tracy, M. McHugh, W. F. Brown, E. Metter

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

Objective: Using a clinical electromyographic (EMG) protocol, motor units were sampled from the quadriceps femoris during isometric contractions at fixed force levels to examine how average motor unit size and firing rate relate to force generation. Methods: Mean firing rates (mFRs) and sizes (mean surface-detected motor unit action potential (mS-MUAP area) of samples of active motor units were assessed at various force levels in 79 subjects. Results: MS-MUAP size increased force generation, while mFR remained relatively constant up to 30% of a maximal force and increased appreciably only at higher force levels. A relationship was found between muscle force and mS-MUAP area (r2 = 0.67), mFR (r2 = 0.38), and the product of mS-MUAP area and mFR (mS-MUAP·mFR) (r2 = 0.70). Conclusions: The results support the hypothesis that motor units are recruited in an orderly manner during forceful contractions, and that in large muscles only at higher levels of contraction (> 30% MVC) do mFRs increase appreciably. MS-MUAP and mFR can be assessed using clinical EMG techniques and they may provide a physiological basis for analyzing the role of motor units during muscle force generation.

Original languageEnglish (US)
Pages (from-to)1270-1275
Number of pages6
JournalClinical Neurophysiology
Volume110
Issue number7
DOIs
StatePublished - Jul 1 1999
Externally publishedYes

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Muscles
Isometric Contraction
Quadriceps Muscle
Clinical Protocols
Action Potentials

All Science Journal Classification (ASJC) codes

  • Clinical Neurology
  • Radiology Nuclear Medicine and imaging
  • Neurology
  • Sensory Systems
  • Physiology (medical)

Cite this

Conwit, R. A., Stashuk, D., Tracy, B., McHugh, M., Brown, W. F., & Metter, E. (1999). The relationship of motor unit size, firing rate and force. Clinical Neurophysiology, 110(7), 1270-1275. https://doi.org/10.1016/S1388-2457(99)00054-1

The relationship of motor unit size, firing rate and force. / Conwit, R. A.; Stashuk, D.; Tracy, B.; McHugh, M.; Brown, W. F.; Metter, E.

In: Clinical Neurophysiology, Vol. 110, No. 7, 01.07.1999, p. 1270-1275.

Research output: Contribution to journalArticle

Conwit, RA, Stashuk, D, Tracy, B, McHugh, M, Brown, WF & Metter, E 1999, 'The relationship of motor unit size, firing rate and force', Clinical Neurophysiology, vol. 110, no. 7, pp. 1270-1275. https://doi.org/10.1016/S1388-2457(99)00054-1
Conwit, R. A. ; Stashuk, D. ; Tracy, B. ; McHugh, M. ; Brown, W. F. ; Metter, E. / The relationship of motor unit size, firing rate and force. In: Clinical Neurophysiology. 1999 ; Vol. 110, No. 7. pp. 1270-1275.
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