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Relationships between surface EMG variables and motor unit firing rates

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Abstract

Although surface electromyography (sEMG) is a widely used electrophysiological technique, its physiological interpretation remains somewhat controversial. This study examined the relationship between motor unit firing rates (MUFR) and the root mean square (RMS) amplitude and mean power frequency (MPF) of the sEMG signal in the biceps brachii. Eleven subjects performed maximal isometric elbow flexion while indwelling and sEMG recordings were obtained from the biceps. The RMS amplitude and MPF of the surface signal, and the mean MUFR from the indwelling signal, were calculated over 500 ms epochs. Group means showed a strong MUFR–RMS amplitude relationship (r 2 = 0.91), but a weak MUFR–MPF relationship (r 2 = 0.20). Using all trials, the MUFR–RMS amplitude (r 2 = 0.19) and MUFR–MPF (r 2 = 0.0037) relationships were much weaker. Within individual subjects, the MUFR–RMS amplitude (mean r 2 = 0.13 ± 0.17) and the MUFR–MPF (mean r 2 = 0.040 ± 0.041) relationships were also weak. These results suggest that MUFR cannot be predicted from the characteristics of the sEMG signal.

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Acknowledgments

This project was supported by a grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada, awarded to D.A. Gabriel.

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Authors and Affiliations

  1. Department of Kinesiology, University of Massachusetts, Amherst, MA, USA

    Anita Christie & Gary Kamen

  2. Department of Physical Education and Kinesiology, Brock University, St. Catharines, ON, L2S 3A1, Canada

    J. Greig Inglis & David A. Gabriel

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  1. Anita Christie
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  2. J. Greig Inglis
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  3. Gary Kamen
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  4. David A. Gabriel
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Correspondence to David A. Gabriel.

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Christie, A., Greig Inglis, J., Kamen, G. et al. Relationships between surface EMG variables and motor unit firing rates. Eur J Appl Physiol 107, 177–185 (2009). https://doi.org/10.1007/s00421-009-1113-7

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