Sex- and fiber-type-related contractile properties in human single muscle fiber

Abstract

This study aimed to examine the distribution and contractile properties of single muscle fiber sex/myosin heavy chain (MHC) type-related dif-ferences and to evaluate the correlation of cross-sectional area (CSA) and specific force (SF) in a single muscle fiber. Six young men and six young women were participated in this study. Muscle sample was ob-tained from vastus lateralis muscle. To examine potential gender differ-ences within each fiber contractile properties (CSA, maximal isometric force, SF, maximal shortening velocity) and relationship between CSA and SF of single fiber using Pearson correlation. After mechanical mea-surements, single muscle fiber determined MHC isoforms using silver stain. MHC isoform composition did not differ by sex (chi-square=6.978, P=0.073). There were sex-related differences in CSA and maximal iso-metric force (P < 0.05), but no fiber type-related differences (P > 0.05). Related to SF and maximal shortening velocity, there were no sex-relat-ed differences only fiber type-related differences (P < 0.05). However, there were differences in SF between single fiber types in men but not in women. A negative correlation was found between CSA and SF in both men and women (P < 0.05). It is suggested that there might be dif-ferent mechanical properties of cross-bridges according to sex.