Dissociation of the electrical and contractile properties in single human motor units during fatigue

Authors

  • K. Ming Chan MD, FRCP(C),

    Corresponding author
    1. Department of Neurology, New England Medical Center, Boston, Massachusetts, USA
    • Division of Neuroscience, 513 Heritage Medical Research Center, University of Alberta, Edmonton, Alberta, T6G 2S2 Canada
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  • Leonard P. Andres MSc,

    1. Nutrition, Exercise Physiology & Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research 1Center on Aging at Tufts University, Boston, Massachusetts, USA
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  • Yelena Polykovskaya MD,

    1. Department of Neurology, New England Medical Center, Boston, Massachusetts, USA
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  • William F. Brown MD, FRCP(C)

    1. Department of Neurology, New England Medical Center, Boston, Massachusetts, USA
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Abstract

The surface EMG area often exhibits progressive enlargement during a submaximal fatiguing contraction, but the underlying reasons still remain uncertain. Fatigue-induced changes in the surface-detected motor unit action potentials (S-MUAPs) of 10 human thenar motor units (MUs) with widely differing physiological properties were examined. After 2 min of repetitive 40-Hz stimulation, the size of the S-MUAPs of all MUs increased, the magnitude of which was negatively correlated with their tetanic tension changes. These findings suggest that during muscle fatigue, in addition to reflecting recruitment of new MUs and increases in firing rates of the active MUs, the surface EMG may also be markedly influenced by changes in the S-MUAPs, especially in fast fatigable muscles. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21: 1786–1789, 1998

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