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Exerc Sci > Volume 21(3); 2012 > Article
Exercise Science 2012;21(3): 309-318. doi: https://doi.org/10.15857/ksep.2012.21.3.309
노인과 성인의 단일 근섬유 아형에 따른 수축 특성과 형태의 비교
최승준1, 임재영2
Age-related changes in contractile properties and morphology on chemically skinned single fibers from young and old human skeletal muscles.
Studies using human model reported inconsistent results on the intrinsic contractile properties of single muscle fiber. To extensively test aging effect on the innate myofilament characteristics and morphology, functional assay of chemically skinned vastus lateralis muscle fiber(15 °C) were investigated from young(25±2 yrs) and old(78±2 yrs) healthy human subjects(N=10 and 8 for young, and old respectively). Fiber cross sectional area(CSA) was measured by 3 dimensional microscopy, peak Ca2+-activated force and maximal shortening velocity(Vo) were measured by slack test procedure. Fiber myosin heavy chain(MHC) isoform was determined by gel electrophoresis and silver staining. Single muscle fiber assays showed fiber CSA and maximal Ca2+-activated force(mN) in old adults type I fiber were 15 % bigger and 18 % greater compared to the corresponding MHC isoform fibers from young adults(p< .05). However, specific force(maximal Ca2+-activated force normalized by fiber CSA, kN/m2) of type I fiber was identical between age group, which suggested that the greater Ca2+-activated force(mN) of type I fiber is resulted from the bigger fiber CSA. Otherwise, type IIa and IIa/IIx fibers showed no difference on fiber CSA and Po between age groups. There is no difference on shortening velocity in type I and IIa fibers between young and old, type IIa/IIx fiber in old adults showed substantially slower Vo than young adults type IIa/IIx fibers(33 %, p< .05). Linear regression modeling to identify relationship between fiber CSA and force generating ability showed strong direct relationship(p< .001) with no aging effect. Therefore, our result indicated maintained contractile properties of myofilament lattice regardless of age. Collectively, the declines of the muscular strength with aging appeared to be due to the quantitative reduction rather than qualitative impairment of single muscle fiber.
Key words: Aging, Single muscle fiber, MHC isoform, Maximal isometric force
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