Time course of hypertrophic adaptations of the anterior latissimus dorsi muscle to stretch overload in aged Japanese quail.

The purpose of this study was to determine if aged Japanese quail demonstrated an altered time course of change in the morphology of the anterior latissimus dorsi (ALD) muscle during the first two weeks of hypertrophy induced by stretch overload. The left wing of adult (12 weeks of age) and aged (90 weeks of age) birds were weighted with 10% of their body weight; the right wing served as the intra-animal control. Thirteen to sixteen birds from each age group were killed after 7 and 14 days of stretch overload. Total fiber number was quantified by counting all the fibers in a transverse section from the mid-belly of the ALD muscle. The aged ALD retained the ability to increase the mass and total fiber number of the stretched ALD after 7 (82%, 16%) and 14 (102%, 19%) days of stretch overload. However, there was a main effect of age on the capacity to increase muscle mass and total fiber number after stretch overload. These results suggest that aging diminishes the increase and alters the time course of adaptation in fiber number and myofibrillar mass of the stretch overloaded ALD during the first two weeks of stretch overload.