Macromolecular composition of fast, slow and cardiac muscles of chick during incubation

Total muscle mass increases about five-fold in fast (anterior latissimus dorsi: ALD) and slow (posterior latissimus dorsi: PLD) muscles and 30-fold in cardiac muscle between the 12th and 20th d of incubation. 2. Increase in muscle protein does not parallel the rise in muscle RNA. 3. The DNA concentration of the ALD muscle decreases while that of the heart and PLD muscle show an increase between 8 and 12 d and a steady decrease thereafter. 4. The increase in glycogen concentration is greater in heart than in ALD and PLD up to the 20th d; 1 d after hatching, ALD has more glycogen than PLD.