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Abstract

Between 0 and 266 days of age the weight of the pectoral and gastrocnemius muscles of chickens increased 300–600- and 40–90-fold respectively depending on the breed and sex. In both muscles the mean cross-sectional area of the fibres and the total number of nuclei (estimated from DNA determination) maintained a constant ratio during growth. This suggests that for individual fibres the cross-sectional area increased in proportion to the number of nuclei. This phenomenon is discussed in relation to current knowledge concerning the mode of growth and multinucleation of skeletal muscle fibres.

In the pectoral muscle, between 0 and 266 days, the cross-sectional area of the fibres increased in proportion to the two-thirds power of the muscle weight, which suggests that the length and diameter of the fibres maintained a constant ratio. The same relationship existed for the gastrocnemius for two months, after which the fibre cross-sectional area increased in proportion to the muscle weight, which suggests that the fibre length was then constant.