Expression of quality control proteins in skeletal muscle samples from active young (YA), and sedentary young (YS), middle-aged (MAS), and older (OS) participants. (A) Western blot analysis of mitochondrial fusion proteins. (B) Western blot analysis of mitochondrial fission proteins. (C) Western blot analysis of autophagy proteins. (D) Western blot analysis of mitochondrial content (OXPHOS, complexes I-V and Total). Values were normalized to α-tubulin and a loading control. Data are presented as Mean and SD for figures A, B, and C, and as Mean and SE for figure D. Results are expressed as arbitrary units (AU); Vertical and horizontal dividing lines were used in the Western blot images to present lanes from the same gel that were reorganized for presentation purpose; n = 5–17 per group. *p < .05 vs YS, MAS, and OS **p < .05 vs MAS and OS, ***p < .05 vs MAS, § p < .05 vs YS, §§ p < .05 vs YA and YS.