Tissue composition affects measures of postabsorptive human skeletal muscle metabolism: Comparison across genders

Despite clear anthropomorphic differences, gender differences in human skel etal muscle protein and carbohydrate metabolism have not been carefully exa mined. We compared postabsorptive forearm glucose, oxygen, and lactate bala nces and forearm protein kinetics between 40 male and 36 female subjects. F orearm composition was measured in a subset of 17 subjects (8 males and 9 f emales) using multislice magnetic resonance imaging. Oxygen uptake, net phe nylalanine release, and estimated rates of forearm protein synthesis and de gradation were greater in male than in female subjects when expressed as th e rate per 100 mt forearm volume (P < 0.05). In males, however, muscle acco unted for 58% of forearm volume, compared with 46% in females (P < 0.001). When phenylalanine balance, protein degradation and synthesis, and glucose and oxygen uptake were expressed per 100 mt forearm muscle, there were no s ignificant differences across gender. Likewise, the extraction fractions fo r oxygen, glucose, phenylalanine, and labeled phenylalanine were comparable in males and females. We conclude that cross-gender comparisons of metabol ic variables must accommodate differences in tissue composition. These data indicate that in the postabsorptive state, skeletal muscle metabolism of g lucose, protein, and oxygen do not differ by gender in healthy young humans .