DEVELOPMENT OF FIBER TYPE AREAS FROM CHILDHOOD TO ADULTHOOD IN VASTUS LATERALIS
Authors: Esbjörnsson Mona , Dahlström Monica , Jansson Eva 
Published: June 2021

It is well known that cross‐sectional areas (CSA) of various skeletal muscle fiber types differ between genders in adults. Generally, CSA of muscle fiber areas is larger in men compared to women. Moreover, CSA of type IIA fibers is the largest in men whereas CSA of type I fibers are the largest in women (Glenmark et al. Acta Physiol Scand. 1992; 146:251–9, Simoneau et al. Am J Physiol. 1989; 25:567–72). To our knowledge, a gender‐related analysis in this respect has not been performed in biopsy samples from children of both sexes. Thus, the aim was to compare CSA of the various fiber types in children of both sexes with corresponding CSAs in adults of both sexes. 27 healthy children (9.0–12.8 years) and 29 young adults (18.0–24.5 years) were studied. Half of the children had 2–3 weeks before the study started professional dance training (“dancers”). All children in the present study had been active in various sports for 1–6 years, 2h/week. Three of the children had also been dancing 1–2 times/week. Half of the adults had completed a 9 years professional dance education (“dancers”) and rest of them had been physically active around 45 min/week (“non‐dancers”). All women had normal menstrual periods and all girls were premenarche. All subjects and the parents of the children were fully informed verbally and in writing before consenting to participate in the study and approved by the Ethics Committees of the Karolinska Institutet. Muscle biopsies were obtained from vastus lateralis and were taken from “dancers” (children and adults) and adult “non‐dancers” under local anaesthesia of the skin and from non‐dancer children during general anaesthesia when undergoing minor surgery. The biopsies were frozen in isopentane precooled with liquid nitrogen and analyzed histochemically for different fiber types (I, IIA, IIB and IIC) with ATPase stains and were examined morphologically for CSA by planimetry (type I, IIA and IIB) from a NADH‐dehydrogenase stain. Our results show that there were no significant differences in CSA of the various fiber types comparing dancers and non‐ dancers in either children or in young adults. Thus, this statistical outcome allowed us to pool dancers and non‐dancers in further statistical analysis. In children, there were no significant differences in CSA either between genders or between fiber types, with a mean and range of 1923 (750–3018) μm2 independent of fiber type and gender. Comparing children and adults, an interaction was found between age and gender for each fiber type (P < 0.003 – P < 0.001). CSA of the various fiber types in the adult group showed larger CSA in men compared to women, especially for type IIA and IIB as expected: Mean and SD for type I, IIA and IIB was for men 4140 (963), 5130 (980) and 4370 (1100) μm2 and for women 3220 (550) and 3040 (750) and 2310 (600) μm2, respectively. In conclusion, the gender specific pattern, in CSA area of the various fiber types in adults was demonstrated to develops during the transition from childhood to adulthood and that this transition in current study was independent of the various training background.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.