Tendon

Lore & Background

Tendons are composed of dense regular connective tissue, with tenocytes synthesizing an extracellular matrix rich in parallel collagen fibers grouped into fascicles. Each fascicle is bound by an endotendineum, and sets of fascicles are bound by an epitenon, with the whole tendon enclosed by a fascia and paratenon. Normal healthy tendons are anchored to bone by Sharpey's fibres. The dry mass of a tendon is 30–45% of its total mass, with collagen making up 60–85% of that dry mass, primarily type I collagen, though minor collagens (types II, III, IV, V, VI, IX, X) play vital roles in development and function.

Reader's Guide

Tendons are essential for transmitting mechanical forces from muscle contraction to the skeletal system, enabling movement and providing stability. They passively modulate forces during locomotion and, in some cases, function as elastic springs to store and recover energy efficiently, as seen with the Achilles tendon during walking or running. The mechanical properties of tendons depend on collagen fiber diameter, orientation, and crimp structure, which allow flexibility and low compressive stiffness. Proteoglycan components help resist compressive stress and facilitate reversible fibril interactions under tension. Tendon length, determined by genetics, affects muscle size and athletic capability—shorter tendons favor muscle mass in bodybuilding, while longer tendons benefit running and jumping. Understanding tendon structure and function is critical for treating injuries and optimizing performance in sports and rehabilitation.

Did You Know?

• Tendons are made of dense regular connective tissue, with collagen fibers running parallel to each other.
• The dry mass of a tendon is 30–45% of its total mass, of which 60–85% is collagen.
• Tendon length is determined by genetic predisposition and does not increase or decrease in response to environment.