Mammalian Motor Units: Physiological-Histochemical Correlation in Three Types in Cat Gastrocnemius

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Science  12 Nov 1971:
Vol. 174, Issue 4010, pp. 709-712
DOI: 10.1126/science.174.4010.709


The correlation among a variety of physiological properties and the histochemical characteristics of muscle fibers belonging to single motor units in a mixed mammalian muscle is directly demonstrated. The population of motor units making up the cat gastrocnemius was classified into three nonoverlapping groups on the basis of a combination of physiological parameters. The muscle fibers belonging to motor units of each physiological type exhibited a distinctive histochemical profile, such that the three basic histochemical "fiber types" exactly matched the three physiologically defined groups. Within each individual motor unit, the muscle fibers were histochemically uniform.