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.
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.
Authors: S M Ling; R A Conwit; L Talbot; M Shermack; J E Wood; E M Dredge; M J Weeks; D R Abernethy; E J Metter Journal: Osteoarthritis Cartilage Date: 2007-05-31 Impact factor: 6.576
Authors: Daniel R Moore; Kirsten A Burgomaster; Lee M Schofield; Martin J Gibala; Digby G Sale; Stuart M Phillips Journal: Eur J Appl Physiol Date: 2004-08 Impact factor: 3.078
Authors: Peter Sieljacks; Jakob Wang; Thomas Groennebaek; Emil Rindom; Jesper Emil Jakobsgaard; Jon Herskind; Anders Gravholt; Andreas B Møller; Robert V Musci; Frank V de Paoli; Karyn L Hamilton; Benjamin F Miller; Kristian Vissing Journal: Front Physiol Date: 2019-05-29 Impact factor: 4.566