Morphological characteristics of skeletal muscles in relation to gender

The aim of this study was to ascertain whether there are gender-related differences in the morphological characteristics of the soleus and tibialis anterior muscles in young adult and old Fischer 344/Brown Norway F1 rats. We tested 1) whether there was a gender-related difference between the fiber type composition of these muscles, and 2) whether the cross-sectional area of individual muscle fibers demonstrated gender-associated differences, fibers from males being larger than fibers from females. Gender differences were not found in the fiber type composition of the soleus and tibialis anterior muscles, but were present in the single skeletal fiber cross-sectional area of the tibialis anterior muscle. The cross-sectional area of type I fibers in females was greater than that in males at both 12 (16%) and 30 (5%) months of age. In contrast, the cross-sectional area of type Ila fibers of 12-month-old males was larger than that of 12-month-old females. No significant differences between genders were found for the cross-sectional area of type Ilb fibers in either age group. In the soleus muscle, 30-month-old males had larger single fiber cross-sectional areas of both fiber types I and lIa. At 12 months of age, type I fibers from females were larger than those from males. Our findings indicate that gender-related differences exist in the size of individual skeletal fibers from the soleus and tibialis anterior muscles and that they may influence metabolism and the adaptive response to rehabilitation programs.