A Comparative Study of the Anterior Latissimus Dorsi Muscle Following Stretch in the Quail and Chicken
The mechanism of muscle mass increase has long been debated. Fiber hypertrophy and hyperplasia (increased fiber numbers) are two possible factors involved in changing the mass of muscle. Much of the controversy in the literature involves whether or not changes in fiber numbers occur. Weight overloading of the avian wing causes a stretch hypertrophy of the anterior latissimus dorsi (ALD) muscle. In response to 30 days of this stretch, muscle mass, muscle fiber number, cross-sectional area, and muscle length were measured in quail (Cortunix japonica) and chicken (Gallus domesticus). Fiber number was determined by direct count after nitric acid digestion of non-muscle tissue. Calculations were then made for individual fiber mass and corrected muscle mass. The other ALD muscle was not stretched, and was used as an intra-animal control. The quail showed a 209-223% increase in muscle mass and a 25-32% increase in length. No significant differences were seen in fiber count or cross-sectional area. An increase in fiber mass was measured (P=0.046). An 84-92% increase in mass and a 21-29% increase in length in the chickens was also seen. There were no significant differences in fiber count, fiber mass or cross-sectional area. These data supported the working hypothesis that the ALD muscle in both species had hypertrophied, but that this hypertrophy was not due to increases in fiber number in either species.
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