sinew

Sinew is a dense, fibrous tissue that links muscle to bone and transmits muscular force to the skeleton. In anatomy, the term is commonly used to designate a tendon or related aponeurosis. Historically, sinew has also referred to tough connective tissue used in crafts, such as sewing thread and bowstrings.

Tendons are composed predominantly of type I collagen organized into parallel fascicles, surrounded by connective tissue sheaths. Tendon cells, or tenocytes, maintain the extracellular matrix. Tendons have relatively limited vascularity and nerve supply; blood flow mostly comes from surrounding tissues and, where present, synovial sheaths or paratenon.

The primary function of sinews is to transfer force from muscle to bone, producing movement. They can store small amounts of elastic energy and contribute to joint stabilization. Sensory receptors, including Golgi tendon organs at the musculotendinous junction, provide proprioceptive information about tension and help regulate force.

Healing and aging: Tendons heal slowly after injury due to limited blood supply, with repair involving inflammation, fibroplasia, and remodeling that may result in scar tissue and altered mechanical properties. Aging reduces collagen turnover and mechanical strength, raising injury risk. Common problems include tendinopathy, tendinitis, and rupture, particularly in load-bearing or overused tendons such as the Achilles or rotator cuff.