Sinew, commonly known as tendon, is a robust and flexible form of connective tissue found throughout the body. These rope-like structures are responsible for connecting muscles to bones. By transmitting the forces generated by muscle contractions, sinews enable a wide range of body movements. They also contribute to joint stability, allowing for coordinated and controlled motion while assisting in maintaining proper body posture.
The Core Components of Sinew
Sinew is primarily composed of collagen fibers, which constitute between 60% and 85% of its dry weight. The most abundant type is Type I collagen. These collagen molecules are organized in a hierarchical structure, first forming fibrils, then fibers, and finally larger bundles called fascicles, which run parallel to each other. This intricate arrangement of collagen provides the tissue with significant resistance to pulling forces.
Beyond Type I, smaller amounts of other collagen types, such as Type III, are also present. A small percentage of elastin, typically 1% to 2% of the dry weight, is also a component of sinew. While collagen provides strength, elastin contributes limited flexibility, allowing the tissue to stretch slightly and recoil to its original shape without permanent deformation.
The fibers and cells within sinew are embedded in a ground substance, which is mostly water (approximately 70%). This gel-like substance contains large organic molecules. The ground substance facilitates the transport of nutrients and provides lubrication, allowing the collagen fibers to glide smoothly past each other during movement. Tenocytes, a type of fibroblast, are the primary cells responsible for producing and maintaining these extracellular matrix components, ensuring the tissue’s structural integrity.
Sinew’s Strength and Purpose
The unique composition and highly organized structure of sinew directly contribute to its remarkable mechanical properties, particularly its ability to withstand significant tensile loads. The parallel alignment of collagen fibers allows for efficient transmission of force along the length of the tissue. This structural design ensures that the powerful contractions of muscles are effectively transferred to the bones, resulting in movement.
Sinew exhibits a specific mechanical behavior known as viscoelasticity, meaning its response to force depends on the rate at which the force is applied. At low levels of strain, the wavy, crimped pattern of the collagen fibrils straightens out. As force increases, the collagen fibers themselves begin to stretch. This property enables sinew to absorb some mechanical stress and impact during activities, helping to protect muscles from injury.
Beyond force transmission, sinew also plays a significant role in providing stability to joints. Its stiffness allows it to resist large loads with minimal deformation, thereby maintaining joint alignment during movement. The tissue’s ability to adapt its structure and mechanical properties in response to varying mechanical demands further underscores its functional importance in the body.