The calcaneal insertion refers to the anatomical site where the Achilles tendon attaches to the posterior surface of the calcaneus (heel bone). This insertion is critical for transmitting the force generated by the calf muscles to enable plantarflexion of the foot, essential for walking, running, and jumping. Clinically, pathology at this site, such as insertional Achilles tendinopathy, can cause heel pain and impaired mobility, often requiring targeted treatment to restore function.