Structure-Function relationships in the skeletal muscle extracellular matrix

The vast majority of skeletal muscle biomechanical studies have rightly focused on its active contractile prop-erties. However, skeletal muscle passive biomechanical properties have significant clinical impact in aging and disease and are yet incompletely understood. This review focuses on the passive biomechanical properties of the skeletal muscle extracellular matrix (ECM) and suggests aspects of its structural basis. Structural features of the muscle ECM such as perimysial cables, collagen cross-links and endomysial structures have been described, but the way in which these structures combine to create passive biomechanical properties is not completely known. We highlight the presence and organization of perimysial cables. We also demonstrate that the analytical ap-proaches that define passive biomechanical properties are not necessarily straight forward. For example, multiple equations, such as linear, exponential, and polynomial are commonly used to fit raw stress-strain data. Similarly, multiple definitions of zero strain exist that affect muscle biomechanical property calculations. Finally, the appropriate length range over which to measure the mechanical properties is not clear. Overall, this review summarizes our current state of knowledge in these areas and suggests experimental approaches to measuring the structural and functional properties of skeletal muscle.

Automated summary

The majority of skeletal muscle biomechanical studies have primarily focused on its active contractile properties, while its passive biomechanical properties are also clinically significant but not fully understood. This review discusses the passive biomechanical properties of the skeletal muscle extracellular matrix (ECM) and suggests aspects of its structural basis. The presence and organization of perimysial cables are highlighted, and the analytical approaches for defining passive biomechanical properties are shown to be complex. Additionally, the appropriate length range for measuring these properties remains unclear. Overall, this review summarizes our current knowledge in these areas and proposes experimental approaches for studying the structural and functional properties of skeletal muscle.