Metabolic And Morphological Profiles In Skeletal Muscle Of Healthy Girls And Boys

Abstract

In adult skeletal muscle, glycolytic, but not oxidative enzyme activities are generally higher in men than women. Earlier a lower activity of glycolytic enzymes was found in vastus lateralis in boys compared to men. Publications comparing boys and girls are lacking. Secondly, cross-sectional muscle area has earlier been found to statistically be a determinant of glycolytic enzymes in skeletal muscle in a mixed group of men and women. If this is true in children, where influence of sex steroids is less, is not known. PURPOSE: It was hypothesized that the typical adult pattern with higher glycolytic capacity in skeletal muscle of men is not observed in children. A second hypothesis was that cross-sectional fiber area (CSFA) is a determinant of glycolytic enzyme activity in children. METHODS: Percutaneous biopsies were performed in vastus lateralis in 12 girls and 15 boys (10 ± 1 years). Based on their training background the children were assigned to non-dancers (n = 15) or dancers (n = 12), Dahlstrom et al. Acta Physiol Scand 1997 160:49-55. Citrate synthase (CS) and lactate dehydrogenase (LD) were analyzed fluorometrically or spectrophotometrically, fiber type composition by myofibrillar ATPase and CSFA from NADH-dehydrogenase stain. RESULTS: There was no significant difference in CS or LD activity between boys and girls. CS was 0.45 ± 0.07 ukat/g dry muscle in boys and 0.42 ± 0.07 in girls. LD was 24 ± 6 ukat/g dry muscle in boys and 25 ± 7 in girls, with no significant interaction in the ANOVA between sex and training group. CSFAs were of similar size in boys and girls. When all children were included in the analysis, CS was inversely related to type I CSFA (r = -0.62, P < 0.001) and LD was directly related to type IIA (r = 0.63, P < 0.001) as well as to type IIB CSFA (r = 0.72, P < 0.001). CSFA was a significant determinant of CS and of LD, also after adjustment for sex, training and relative fiber type area in a multiple regression analysis. CONCLUSION: In children, CSFA, but not sex, was a strong determinant of LD. This means that CSFA could be a determinant of LD also in adults and thereby contribute to the generally higher LD activity found in men than women, although the influence of sex hormones cannot be excluded. Supported by grants from the Swedish Medical Research Council and the Swedish National Centre for Research in Sports.