MRI Characterization Of Skeletal Muscle Size And Fatty Infiltration In Long-term Trained And Untrained Individuals

Abstract

PURPOSE: We aimed to investigate various body composition measures in highly trained and untrained men and women using whole-body magnetic resonance imaging (MRI). Additionally, correlations between these measures and skeletal muscle gene expression were performed. METHODS: Thirty-six individuals were included: endurance-trained men (ME, n = 8) and women (FE, n = 7), strength-trained men (MS, n = 7) or untrained control men (MC, n = 8) and women (FC, n = 6). Whole-body MRI scans were performed, and m. vastus lateralis biopsies were collected at rest. Cross-sectional area (CSA) and infiltration of muscular adipose tissue (IMAT) were calculated from Mm. pectoralis, M. erector spinae and M. multifidus combined, Mm. quadriceps, and Mm. triceps surae (TS). RESULTS: ME and FE had significantly lower liver fat fraction, visceral fat volume and total body fat mass relative to body weight than MC and FC, respectively. MS had larger CSA across all four muscle groups and less IMAT in all muscles apart from TS (p = 0.053) compared with MC. ME was found to have less IMAT across all muscle groups and a larger CSA in three of the four muscle groups compared with MC. However, the only difference in IMAT between FE and FC was found in Mm. pectoralis. Functional analysis of muscle gene expression of the top 50 genes that correlated most strongly with IMAT revealed a significant enrichment of the AMPK-pathway. CONCLUSIONS: This study suggests that both regular endurance and resistance training are, over time, appropriate to maintain muscle mass and reduced skeletal muscle infiltration of adipose tissue in male adults. Although a significant relationship between IMAT and the AMPK pathway was found, future studies are needed to determine the mechanism by which infiltration of adipose tissue is regulated in muscle.