RESISTANCE TRAINING PROGRESSION: EFFECTS ON THE REMODELING OF THE EXTRACELLULAR MATRIX IN HUMANS

Abstract

Among the adaptations resulting from resistance training (RT), the increase in cross-sectional area of muscle fibers and, consequently, of the entire muscle (i.e., muscle hypertrophy) may contribute to the prevention or mitigation of obesity, type 2 diabetes, and other comorbidities, thereby preventing premature death. However, several aspects are involved in the prescription of RT, which can affect the regulatory mechanisms of muscle hypertrophy in an acute (i.e., response during and after performing a single RT session) and chronic (i.e., adaptations after performing several sessions) manner, are still not well understood. Our laboratory has successfully investigated, through regular funding from FAPESP (#2013/21218-4; #2017/04299-1; #2018/12150-0), the mechanisms involved in RT-induced muscle hypertrophy. In this project, through an intra-subject randomized controlled trial, we will compare the effects of protocols for the progression of strength training by intensity (progINT) and volume (progVOL) on the cross-sectional area of the vastus lateralis muscle and type I and II fibers, as well as the area occupied by myofibrillar and sarcoplasmic content of these fibers, to investigate the occurrence or absence of sarcoplasmic hypertrophy. Additionally, we will investigate the effects of these protocols on extracellular matrix (ECM) remodeling factors (protein content [MMP-2, MMP-9, MMP-14, TIMP-1, TIMP-2], overall MMP activity, ECM content (collagen area per fiber, collagen-1 and 4 protein expression), the abundance of cells residing and interacting with the ECM (macrophages, FAPs, and satellite cells). Finally, we will also investigate the association between muscle and fiber hypertrophy with markers of extracellular matrix remodeling and whether changes in muscle collagen content and ECM remodeling differ between high and low responders to muscle hypertrophy induced by RT. The rationale that led us to these objectives and our hypotheses can be seen in detail throughout this project. (AU)