Myofibril and Mitochondrial Area Changes in Type I and II Fibers Following 10 Weeks of Resistance Training in Previously Untrained Men

• DOI: 10.3389/fphys.2021.728683
• Publication Date: 2021-09-24T16:34:31Z
• Authors: Bradley A. Ruple; Joshua S. Godwin; Paulo H. C. Mesquita; Shelby C. Osburn; Casey L. Sexton; Morgan A. Smith; Jeremy C. Ogletree; Michael D. Goodlett; Joseph L. Edison; Arny A. Ferrando; Andrew D. Fruge; Andreas N. Kavazis; Kaelin C. Young; Michael D. Roberts
• Keywords: Myofibril; Endurance Training; Vastus lateralis muscle

Resistance training increases muscle fiber hypertrophy, but the morphological adaptations that occur within fibers remain largely unresolved. Fifteen males with minimal experience (24±4years, 23.9±3.1kg/m 2 body mass index) performed 10weeks of conventional, full-body resistance (2× weekly). Body composition, radiological density vastus lateralis using peripheral quantitative computed tomography (pQCT), and biopsies were obtained 1week prior to 72h following last bout. Quantification myofibril mitochondrial areas in type I (positive for MyHC I) II IIa/IIx) was immunohistochemistry (IHC) techniques. Relative myosin heavy chain actin protein abundances per wet weight as well citrate synthase (CS) activity assays also on tissue lysates. Training increased whole-body lean mass, mid-thigh cross-sectional area, mean (fCSA), maximal strength values leg press, bench deadlift ( p <0.05). The intracellular area occupied by myofibrils or not altered training, suggesting a proportional expansion fCSA increases. However, our histological analysis unable differentiate whether number girth occurred. did change training. IHC indicated both types =0.018), albeit CS levels remained unaltered discordance between these assays. Interestingly, although pQCT-derived =0.036), suggestive packing, positive association existed training-induced changes this metric r =0.600, =0.018). To summarize, data imply shorter-term promotes disproportional mitochondria fibers. Additionally, biochemical techniques should be viewed independently from one another given lack agreement variables assessed herein. Finally, pQCT may viable tool non-invasively track (specifically density) tissue.