Title: Influence of the NASA SPRINT exercise protocol on myonuclear and satellite cell content of the vastus lateralis and soleus during 70 days of bedrest

• Published in: Physiology (Bethesda, Md.) Md.), 2024-05, Vol.39 (S1)
• Main Authors: Skiles, Chad, Boyd, Gerard, Robbins, Ethan, Gouw, Aaron, Minchev, Kiril, Ryder, Jeffrey, Ploutz-Snyder, Lori
• Format: Article
• Language: English
• ISSN: 1548-9213; 1548-9221
• DOI: 10.1152/physiol.2024.39.S1.2496

Abstract only Objectives: The purpose of this study was to assess the effcacy of the NASA SPRINT exercise protocol in preserving myonuclear and satellite cell number of the quadriceps (vastus lateralis) and triceps surae (soleus) muscles following 70 days of bedrest (i.e., simulated microgravity). These two muscles were the focus of this study because they both atrophy significantly with microgravity exposure in the absence of countermeasures. Hypotheses: The SPRINT exercise protocol will preserve myonuclear number (MNN), myonuclear domain (MND), and satellite cell number (SCN) during 70 days of bedrest. Methods: Subjects were randomized into three groups: bedrest only (BR; n=8, 37±3 y), bedrest with endurance and resistance exercise (BRE; n=9, 34±2 y) and bedrest with endurance and resistance exercise and low dose testosterone injections (BRE+T; n=8, 33±3 y). Muscle biopsies were taken before and at the end of bedrest from the vastus lateralis and soleus, and were sectioned, immunofluorescently stained, and analyzed for MNN (myonuclei/fiber), MND (μm 2 /myonuclei), and SCN (satellite cells/fiber) in slow (myosin heavy chain (MHC) I) and fast (MHC IIa) muscle fibers. SCN was only determined in MHC I fibers for the soleus. Results: MNN, MND, and SCN in MHC I and IIa fibers of the vastus lateralis and soleus were unchanged (p