Relationships between surface-detected EMG signals and motor unit activation

Hiromasa Suzuki, Robin A. Conwit, Dan Stashuk, Lynn Santarsiero, E. Metter

Research output: Contribution to journalArticle

47 Citations (Scopus)

Abstract

Introduction: Surface-detected electromyographic (S-EMG) signals are used in exercise science to assess the extent of muscle activation, muscle fatigue, and neural activity during muscle contraction. However, the relationship has not been studied between S-EMG signal amplitude and motor unit activation at different muscle force levels. Methods: S-EMG signals were measured from 76 healthy subjects during target force levels of 5, 10, 20, 30, and 50% of maximal voluntary contraction (MVC) of the knee extensors over 20-30 s. Mean absolute S-EMG amplitude, surface-detected motor unit action potential amplitude (S-MUAP), motor unit mean firing rate (mFR), and motor unit mean voltage, which is the product of S-MUAP amplitude and mFR. were assessed in the vastus medialis by using EMG signal-decomposition and spike-triggered averaging techniques. Results: Motor unit mean voltage increased to the same degree as mean absolute S-EMG amplitude with increasing force, implying that motor unit size and firing rate explain the increase in mean absolute S-EMG amplitude with increasing force generation. In addition, mean absolute S-EMG amplitude increased linearly during the course of each 20-30 s contraction, with the slope being greater at higher force levels. A small change was observed in the shape of needle-detected motor unit action potentials during the contraction, but this change was not sufficient to explain the large change in mean absolute S-EMG amplitude during the contraction. Conclusion: Mean absolute S-EMG amplitude at different force levels and its changes during the course of a submaximal contraction are dependent on the number of motor units active, their size, and firing rates.

Original languageEnglish (US)
Pages (from-to)1509-1517
Number of pages9
JournalMedicine and Science in Sports and Exercise
Volume34
Issue number9
DOIs
StatePublished - Jan 1 2002
Externally publishedYes

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Action Potentials
Muscles
Muscle Fatigue
Quadriceps Muscle
Muscle Contraction
Needles
Knee
Healthy Volunteers
Exercise

All Science Journal Classification (ASJC) codes

  • Orthopedics and Sports Medicine
  • Physical Therapy, Sports Therapy and Rehabilitation

Cite this

Relationships between surface-detected EMG signals and motor unit activation. / Suzuki, Hiromasa; Conwit, Robin A.; Stashuk, Dan; Santarsiero, Lynn; Metter, E.

In: Medicine and Science in Sports and Exercise, Vol. 34, No. 9, 01.01.2002, p. 1509-1517.

Research output: Contribution to journalArticle

Suzuki, Hiromasa ; Conwit, Robin A. ; Stashuk, Dan ; Santarsiero, Lynn ; Metter, E. / Relationships between surface-detected EMG signals and motor unit activation. In: Medicine and Science in Sports and Exercise. 2002 ; Vol. 34, No. 9. pp. 1509-1517.
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