Metabolic and morphological profile in skeletal muscle of healthy boys and girls

Abstract

It was hypothesized that the typical adult pattern of higher glycolytic capacity in skeletal muscle of males compared to females is not observed in children and that fiber cross‐sectional area (CSA) is a determinant of glycolytic capacity in children. Biopsies were performed in vastus lateralis in 9–12 years‐old healthy boys and girls ( N = 27). Fiber types were classified by myofibrillar ATPase staining and CSA was measured using planimetry. Citrate synthase (CS) and lactate dehydrogenase (LD) were analyzed using fluorometric and spectrophotometric methods. There was no significant difference between boys and girls in CS activity (0.45 ± 0.1 μkat g −1 dry muscle in boys and 0.42 ± 0.1 in girls) or LD activity (24 ± 6 μkat g −1 dry muscle in boys and 25 ± 7 in girls). CSA did not differ between boys and girls. CS was inversely related to type I CSA ( r = −0.62, p < 0.001) and LD was directly related to type IIA ( r = 0.63, p < 0.001) and type IIB CSA ( r = 0.72, p < 0.001). CSA was a significant determinant of CS and LD, even after adjusting for sex and relative fiber type area in multiple regression analysis. This suggests that the typical adult pattern of higher muscle glycolytic capacity in males than in females, as estimated by LD activity, was not observed in children. Sex‐specific patterns in glycolytic capacity thus appear to develop during the transition from childhood to adulthood. In addition, fiber CSA was a strong determinant of both muscle glycolytic and oxidative capacity in children, regardless of sex.

Histological analysis of the medial gastrocnemius muscle in young healthy children

“…In this study, fiber size variability was present in the MG of young healthy children but it was similar between the different fiber types. Our data of fiber size variability corroborate the findings in the vastus lateralis muscle in children aged 9-11 years showing a coefficient of variation of 28% ± 6 for boys and 30% ± 8 for girls in type I fibers and of 21% ± 5 (boys) and 23% ± 7 (girls) for type IIa fibers (Esbjörnsson et al, 2022). In the peroneus brevis muscle, a CV of 17% for type I and II fibers was reported in samples issued from pathology data of children aged 5-13 years (Rose et al, 1994).…”

“…This implies that the normal values of (very) young children differ from normal values of older children and using inappropriate age range data for comparison may lead to data misinterpretation. Additional drawbacks of the performed studies in children, for example, are 1) the age range of included subjects with scarce data on very young children ( Valentine et al, 2019 ; Esbjörnsson et al, 2022 ; Hester et al, 2022 ), 2) the use of data from autopsy specimen ( Jennekens, Tomlinson, and Walton, 1971 ; Johnson et al, 1973 ; Lexell et al, 1992 ), 3) from very active children ( Esbjörnsson et al, 2021 ), 4) or from subjects who underwent surgery that limited their physical activity ( Domenighetti et al, 2018 ), 5) the absence of data on fiber size for the leg muscle ( Kriketos et al, 1997 ), 6) the lack of information on effect of gender if any ( Lee et al, 2006 ; Delhaas et al, 2013 ) etc., … It seems that sex related differences in fiber pattern development occur during the transition from childhood to adulthood ( Esbjörnsson et al, 2021 ), but whether sex related differences are already present at younger age is not yet known. Furthermore, while only a couple of studies have been performed on the satellite cells in healthy adults ( Kadi et al, 1999 ; Carlson et al, 2009 ; Mackey et al, 2009 ; Mackey et al, 2010 ; Bankolé et al, 2013 ), there are almost no data on healthy young children ( Saito, 1985 ; Maier and Bornemann, 1999 ; Verdijk et al, 2014 ; Corvelyn et al, 2020 ).…”

“…This implies that the normal values of (very) young children differ from normal values of older children and using inappropriate age range data for comparison may lead to data misinterpretation. Additional drawbacks of the performed studies in children, for example, are 1) the age range of included subjects with scarce data on very young children (Valentine et al, 2019;Esbjörnsson et al, 2022;Hester et al, 2022), 2) the use of data from autopsy specimen (Jennekens, Tomlinson, and Walton, 1971;Johnson et al, 1973;Lexell et al, 1992), 3) from very active children (Esbjörnsson et al, 2021), 4) or from subjects who underwent surgery that limited their physical activity (Domenighetti et al, 2018), 5) the absence of data on fiber size for the leg muscle (Kriketos et al, 1997), 6) the lack of information on effect of gender if any (Lee et al, 2006;Delhaas et al, 2013) etc., . .…”