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J Gerontol A Biol Sci Med Sci. 1995 Nov;50 Spec No:91-5.

Motor units: remodeling in aged animals.

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Department of Clinical Neurophysiology, Karolinska Hospital, Stockholm, Sweden.


The effects of aging on motor units of different types and the spatial arrangement of motor units are discussed. This article is, however, not a comprehensive survey of the literature, but rather a summary of our own results with the addition of relevant reports. The glycogen depletion technique was used to identify the muscle fibers in a motor unit (motor unit fibers). The motor unit fibers were subsequently characterized according to immunocytochemical, enzyme-histochemical and morphometrical properties, and the spatial arrangement was determined with the aid of a computer-assisted model. An age-related motor unit transformation was observed in both fast- and slow-twitch rat skeletal muscles as was a rearrangement of motor unit fibers. The spatial redistribution of motor unit fibers, higher innervation ratios, and larger motor unit territories in old age indicate an age-related denervation-reinnervation process due to loss of alpha-motoneurones.

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