Reliability of spike triggered averaging of the surface electromyogram for motor unit action potential estimation

Authors

  • Xiaogang Hu PhD,

    Corresponding author
    1. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, USA
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  • William Z. Rymer MD, PhD,

    1. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, USA
    2. Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
    3. Department of Physiology, Northwestern University, Chicago, Illinois, USA
    4. Department of Biomedical Engineering, Northwestern University, Chicago, Illinois, USA
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  • Nina L. Suresh PhD

    1. Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, Illinois, USA
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  • This study was supported by NIH R24 HD50821-07 awarded to W.Z.R.

ABSTRACT

Introduction: The reliability of estimated motor unit parameters using spike triggered averaging (STA) of the surface electromyogram (sEMG) has not been tested thoroughly. We investigated factors that may induce amplitude bias in estimated motor unit action potentials (MUAPs) and shape variations. Methods: An sEMG record was simulated. MUAPs were then estimated from the STA of the simulated EMG. Results: Variations in MUAP duration led to under-estimation of real MUAP amplitude, while synchronized firing led to over-estimation of amplitude. Spurious firing resulted in over-estimation of the amplitude of small motor units but under-estimation of the amplitude of large ones. Variability in amplitude and high firing rates had minimal influence on amplitude estimation. High firing rates and variation in MUAP duration led to large variations in MUAP shape. Estimation errors also correlated with shape variations. Conclusions: Recommendations to enhance the accuracy of the STA estimates have been proposed. Muscle Nerve 48: 557–570, 2013

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