The calcaneal tendon, also known as the tendon of Achilles, is a posterior leg tendon that is formed when the soleus muscle tendon joins the gastrocnemius tendon. The gastrocnemius (calf) and soleus muscles are part of the superficial posterior compartment group, which also contains the popliteus and plantaris muscles; hence, the calcaneal tendon is a part of this group, which makes up its posterior surface.
The purpose of the calcaneal tendon is to attach the soleus muscles, the calf muscles (plantaris and gastrocnemius) to the heel bone, scientifically known as the calcaneus. The plantaris muscle tendon, if present, assists in this process because it inserts into the calcaneal tendon's medial border.
The calcaneal tendon is the strongest and thickest and human tendon, with it being able to withhold a stress of 3.9 times a person's body weight when walking and its narrowest part above its insertion being four centimeters thick. The tendon starts in the middle of the calf and extends approximately 15 centimeters in length, down to the heel, and passes vertically down behind the ankle.