Age-related changes in the mechanical properties of the epimysium in skeletal muscles of rats

Abstract

Skeletal muscle is composed of muscle fibers and an extracellular matrix (ECM). The collagen fiber network of the ECM is a major contributor to the passive force of skeletal muscles at high strain. We investigated the effect of aging on the biomechanical and structural properties of epimysium of the tibialis anterior muscles (TBA) of rats to understand the mechanisms responsible for the age-related changes. The biomechanical properties were tested directly in vitro by uniaxial extension of epimysium. The presence of age-related changes in the arrangement and size of the collagen fibrils in the epimysium was examined by scanning electron microscopy (SEM). A mathematical model was subsequently developed based on the structure-function relationships that predicted the compliance of the epimysium. Biomechanically the epimysium from old rats was much stiffer than that of the young rats. No differences were found in the ultrastructure and thickness of the epimysium or size of the collagen fibrils between young and old rats. The changes in the arrangement and size of the collagen fibrils do not appear to be the principal cause of the increased stiffness of the epimysium from the old rats. Other changes in the structural composition of the epimysium from old rats likely has a strong effect on the increased stiffness. The age-related increase in the stiffness of the epimysium could play an important role in the impaired lateral force transmission in the muscles of the elderly.

Stuck in gear: age-related loss of variable gearing in skeletal muscle

“…3) decreased with age. Decreases in active muscle stress with age have largely been attributed to an increased contribution of connective tissues (Kjaer, 2004;Gao et al, 2008;Kragstrup et al, 2011) and fat (Kent-Braun et al, 2000) to muscle cross-sectional area. However, the present results suggest that changes in pennation angle during contraction may also contribute to the decrease in stress in old muscles.…”

Observation of Age‐Related Decline in the Performance of the Transverse Abdominis Muscle

“…Rapid muscle activation requires the contractile apparatus to function effectively and there are, of course, likely to be multiple factors responsible for the slower TrA onset (D) seen in the older subjects. These include age-related changes to the extracellular matrix such as increased volume [26] and increased stiffness [27] as well as the number of crosslinks in the matrix itself [28]. Myogenic factors should also be considered as likely contributors to the results as ageing is typically associated with up-regulation of negative markers of muscle differentiation as well as down-regulation of positive markers of differentiation.…”

Satellite Cells and the Muscle Stem Cell Niche

“…Recent studies reveal a previously unappreciated role for the stiffness of the ECM in regulating satellite cell proliferation and differentiation. Resting healthy skeletal muscles and cultured myotubes possess a similar elastic stiffness (elastic modulus ϳ12 kPa) (106,152), whereas aged (184,444) and dystrophic (152) skeletal muscles are apparently stiffer (elastic modulus ϳ418 kPa). These changes of stiffness are presumably due to increased extracellular matrix deposition, in particular collagen deposition by fibroblasts, a result of repeated muscle regeneration.…”