A histochemical study of developing human skeletal muscle

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Abstract
The sequence of events in development of the 2 histochemical fiber types which are presnet in human muscle is reported. The myosin ATPase [adenine triphosphatase] reaction is most useful for fiber typing during the early weeks of gestation. Early myotubes are predominantly members of the type n population and are larger in size than the later developing type I fibers. Between 15 and 20 weeks, the type I fibers grow rapidly and become larger than the type n fibers. Mitochondrial reactions are intense in all fibers during the period of myofibrillary formation. The results demonstrate that the 2 muscle types develop in the human embryo as separate populations. A possible relationship between mitochondria and the band alignment of new myofilaments is suggested.