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Achilles tendon

Recommended video: Muscles of the posterior leg [18:08]
Origins, insertions, innervation and functions of the muscles of the posterior leg.
Achilles tendon (tendo calcaneus)

Calcaneal tendon, or the Achilles tendon is the strongest and thickest tendon of the human musculoskeletal system. It is the common tendon of the two constituting muscles of the triceps surae; gastrocnemius and soleus, attaching them to the posterior surface of calcaneus bone. The calcaneal tendon has a couple of important functions; it enables the superficial posterior leg muscles to plantarflex the foot and stabilizes the ankle joint during the gait cycle.

There is a fun fact regarding how the calcaneal tendon got its eponym; the Achilles tendon. The story is related to the Greek mythology hero, Achilles. According to the myth, the entire Achilles’ body was bulletproof, except for the calcaneal tendon.

He eventually died in the Trojan war as an arrow pierced his calcaneal tendon. Based on this myth, the Achilles tendon got its name and is used in common language to describe a person’s weakest spot.

Key facts about the Achilles tendon
Definition Common tendon of superficial posterior leg muscles; gastrocnemius, soleus and plantaris
Function Plantar flexion of the foot, ankle joint stabilizer
Clinical relations Thompson’s test, Achilles tendon rupture

This article will discuss the anatomy and function of the Achilles tendon.

  1. Anatomy
  2. Function
  3. Achilles tendon rupture
  4. Thompson’s test
  5. Sources
+ Show all


The calcaneal tendon originates as a wide aponeurotic sheath from the distal end of the gastrocnemius muscle. It then courses downwards, gradually rounding up in shape. The tendon is joined by the soleus muscle fibers about 4 centimeters above the ankle joint. Finally, the tendon passes over the ankle joint and inserts onto the posterior surface of calcaneus.

The tendon fibers do not run strictly vertically as they descend, but rather they spiral laterally up to 90 degrees once the soleus fibers join the tendon. This results in the soleus fibers inserting medially and the gastrocnemius inserting laterally on the attachment surface of the calcaneus. Sometimes, the tendon of the plantaris muscle fuses with the calcaneal tendon, while in other cases, it inserts separately onto the plantar aponeurosis.

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The Achilles tendon is innervated by the sural nerve. Note that the sural nerve crosses the upper half of the tendon’s lateral border, which is a common spot of the nerve’s injury during surgical procedures. Vascular supply to the tendon comes from two sources; proximal and distal thirds are supplied by the posterior tibial artery, while the fibular (peroneal) artery supplies the middle third of the tendon.


The main Achilles tendon function is to enable the triceps surae muscles to plantarflex the foot.

Besides this, the tendon is crucial for normal biomechanics of the ankle joint. The spiralling of the fibers just before their insertion creates an area of concentrated stress conveyed to the calcaneus. This design of the tendon’s insertion enables adequate force transmission to the foot during walking, running and jumping. In young individuals, the tendon can bear up to 12 times its body weight during running, while in the elderly the level of endurance drops. This is one of the reasons why Achilles tendon tears are more common in the elderly population.

Learn more about the Achilles tendon anatomy and function with our 3D video tutorials.

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