RE-EXAMINATION OF BIPHASIC THEORY OF SKELETAL-MUSCLE GROWTH

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  • 1 January 1977
    • journal article
    • research article
    • Vol. 123  (APR) , 313-324
Abstract
Because of the importance of fiber diameter measurements, the biphasic theory of skeletal muscle growth and development was re-evaluated. This theory proposed an initial monophasic distribution of muscle fibers which changed to a biphasic distribution during development. The theory was based on observations made on certain muscles in mice, where 2 distinct populations of fiber diameters (20 and 40 .mu.m) contributed to the biphasic distribution. Cross sections of frozen biceps brachii of mice in rigor mortis were examined. The rigor state was used to avoid complications produced by thaw-rigor contraction. The diameters of the outermost and intermost fibers were significantly different. If the outer and inner fibers were combined to form 1 group, no significant difference between this group and other random groups was found. The distributions of all groups were monophasic. The diameters of isolated fibers from mice and rats also displayed a monophasic distribution. The biphasic theory of muscle growth was untenable. Some variables which may occur in fiber size and shape were discussed.