In older individuals, hypertrophy from progressive resistance training (PRT) is compromised in approximately one-third of participants in exercise trials. The objective of this study was to establish novel relationships between baseline muscle features and/or their PRT-induced change in vastus lateralis muscle biopsies with hypertrophy outcomes. Multiple linear regression analyses adjusted for sex were performed on phenotypic data from older adults (n = 48 participants, 70.8 ± 4.5 yr) completing 14 wk of PRT. Results show that baseline muscle size associates with growth regardless of hypertrophy outcome measure [fiber cross-sectional area (fCSA), β = -0.76, Adj. P < 0.01; thigh muscle area by computed tomography (CT), β = -0.75, Adj. P < 0.01; dual-energy X-ray absorptiometry (DXA) thigh lean mass, β = -0.47, Adj. P < 0.05]. Furthermore, loosely packed collagen organization (CO, β = -0.44, Adj. P < 0.05) and abundance of CD11bþ/CD206- immune cells (β = -0.36, Adj. P = 0.10) were negatively associated with whole muscle hypertrophy, with a significant sex interaction on the latter. In addition, a composite hypertrophy score generated using all three measures reinforces significant fiber level findings that changes in myonuclei (MN) (b = 0.67, Adj. P < 0.01), changes in immune cells (b = 0.48, Adj. P < 0.05; both CD11bþ/CD206 þ and CD11bþ/CD206- cells), and capillary density (b = 0.56, Adj. P < 0.01) are significantly associated with growth. Exploratory single-cell RNA-sequencing of CD11bþ cells in muscle in response to resistance exercise showed that macrophages have a mixed phenotype. Collagen associations with macrophages may be an important aspect in muscle response heterogeneity. Detailed histological phenotyping of muscle combined with multiple measures of growth response to resistance training in older persons identify potential new mechanisms underlying response heterogeneity and possible sex differences. NEW & NOTEWORTHY Extensive analyses of muscle features associated with muscle size and resistance training response in older persons, including sex differences, and evaluation of multiple measures of hypertrophy are discussed. Collagen organization and CD11b-expressing immune cells offer potential new targets to augment growth response in older individuals. A hypertrophy composite score reveals that changes in immune cells, myonuclei, and capillary density are critically important for overall muscle growth while sc-RNAseq reveals evidence for macrophage heterogeneity.
|Number of pages||16|
|Journal||Journal of Applied Physiology|
|State||Published - Jun 2022|
Bibliographical noteFunding Information:
The authors thank each of valuable research participants for time, effort, and dedication given during the study. We thank Tara Bennett PA-C and Dr. Sam Windham for performing muscle biopsies and Dr. Janna Jackson for performing immunohistochemistry. We also thank Dr. Ameya Kulkarni and Dr. Nir Barzilai of the Albert Einstein School of Medicine Nathan Shock Center for assistance with RNA sequencing data. Additional thanks goes to Dr. R. Grace Walton and Alex Simmons for technical expertise in the analysis of capillaries and collagen. The study was funded by the National Institutes of Health (NIH) National Institute on Aging Grant AG046920 and supported by the NIH Clinical and Translational Science Awards (CTSA) (UL1TR001998) at the University of Kentucky and the NIH CTSA (UL1TR000165) at the University of Alabama at Birmingham. This study was also supported by an award from the Glenn Foundation for Medical Research.
The study was funded by the National Institutes of Health (NIH) National Institute on Aging Grant AG046920 and supported by the NIH Clinical and Translational Science Awards (CTSA) (UL1TR001998) at the University of Kentucky and the NIH CTSA (UL1TR000165) at the University of Alabama at Birmingham. This study was also supported by an award from the Glenn Foundation for Medical Research.
Copyright © 2022 the American Physiological Society.
- muscle hypertrophy
- resistance training
ASJC Scopus subject areas
- Physiology (medical)