Immobilization-induced changes in motor unit force and fatigability in the cat

Authors

  • Dr., PhD Grant A. Robinson,

    1. The Department of Physiology, University of Arizona, Tucson, Arizona
    Current affiliation:
    1. The Research Institute, Montreal General Hospital, Montreal, Quebec, Canada
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  • Dr., PhD Roger M. Enoka,

    1. Exercise and Sport Sciences, University of Arizona, Tucson, Arizona
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  • Dr., PhD Douglas G. Stuart

    Corresponding author
    1. The Department of Physiology, University of Arizona, Tucson, Arizona
    • Department of Physiology, Arizona Health Sciences Center, University of Arizona, Tucson, AZ 85724
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Abstract

The purpose of this study was to examine the effects of 3 weeks of immobilization on the mechanical properties of motor units in a cat hindlimb muscle. The muscle, tibialis posterior, was immobilized in a shortened position. Motor units were classified as type FF, F(int), FR, or S. Force, axonal conduction velocity, fatigability, and proportions of motor unit types were compared in control and immobilized muscles. All properties exhibited some change after immobilization, including slower axonal conduction velocities, greater twitch forces, slower twitch contraction times, and greater tetanic forces. In addition, most motor units were less fatigable after immobilization. The number of motor units that could not be included in one of the four classification categories increased significantly after immobilization; these units exhibited normal axon conductivity but failed to produce measurable force or associated EMG. Short-term immobilization induced a variety of physiological adaptations in neuromuscular processes that varied with motor unit type.

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