Adams G R
Department of Physiology and Biophysics, University of California, Irvine, USA.
Exerc Sport Sci Rev. 1998;26:31-60.
Adaptations in muscle mass stimulated by changes in muscle loading state entail alternations in the synthesis and degradation of myofiber proteins and the modulation of myonuclear number such that the ratio between the number of myonuclei and the size of the myofibers remains relatively constant. As depicted schematically in Figure 2.6, the literature regarding the role of IGF-in mediating muscle adaptation to alterations in loading state suggests the following conclusions: During periods of increased loading, myofibers upregulate the expression and secretion of IGF-I. Acting as an autocrine and/or paracrine growth factor, IGF-I stimulates myofiber anabolic processes. Acting as a paracrine growth factor, IGF-I also stimulates adjacent satellite cells to enter the cell cycle and proliferate. Continued myofiber production of IGF-I stimulates some satellite cells to differentiate and then fuse with myofibers, thus providing additional myonuclei in order to maintain or reestablish the myonucleus to myofiber size ratios of the enlarged myofibers.
肌肉负荷状态变化所刺激的肌肉质量适应，需要肌纤维蛋白合成与降解的改变以及肌核数量的调节，以使肌核数量与肌纤维大小之间的比例保持相对恒定。如图2.6示意所示，关于胰岛素样生长因子-I（IGF-I）在介导肌肉适应负荷状态改变中的作用的文献表明了以下结论：在负荷增加期间，肌纤维上调IGF-I的表达和分泌。作为一种自分泌和/或旁分泌生长因子，IGF-I刺激肌纤维合成代谢过程。作为旁分泌生长因子，IGF-I还刺激相邻的卫星细胞进入细胞周期并增殖。肌纤维持续产生IGF-I刺激一些卫星细胞分化，然后与肌纤维融合，从而提供额外的肌核，以维持或重新建立增大的肌纤维的肌核与肌纤维大小比例。
