Anatomy of the Achilles tendon: a simple explanation of its function, location, structure and characteristics

The Achilles tendon is a highly complex tendon in the human body. A basic understanding of its function and structure helps to get a better feel for your own Achilles tendon.

  1. Function of the Achilles tendon

  2. Location of the Achilles tendon

  3. The bursa – the fluid-filled sac between the Achilles tendon and heel bone

  4. Structure of the Achilles tendon

  5. Blood Circulation and training

1. Function of the Achilles tendon

The Achilles tendon transfers the force from the calf muscles to the foot and enables us to push off from the floor. As the foot lifts, a good, elastic Achilles tendon stores up to 30% of the power that we then need to push off and run forwards. An elastic Achilles tendon is worth its weight in gold when doing sporting activity and if painful should be healed as soon as possible.

30% of the power needed to lift your leg comes from a healthy Achilles tendon


2. Location of the Achilles tendon

In order to locate possible Achilles tendon pain in the foot, we first need to know where the Achilles tendon is.

The Achilles tendon is an important part of the calf muscle. However, unlike the muscle, it is unable to contract. The tendon is made up of connective tissue (collagen type I). It starts at the heel bone and merges with the calf muscle. Anatomy and structure of the Achilles tendon:

3. The bursa – the fluid-filled sac between the Achilles tendon and heel bone

At the bottom end of the Achilles tendon there is a gliding layer, the tendon sheath (bursa). Among other reasons, it is needed there because the tendon moves across other tissue and bones. The bursa ensures that the tendon is able to move without any friction.

Layer of connective tissue: some tendon fibers are surrounded by a thin layer of connective tissue made up of nerves and vessels. This ensures blood and lymph flow.

4. The Achilles tendon

The Achilles tendon is round and has a solid structure. It is shiny white in color and looks like a cable or rope.

The main part of the Achilles tendon is made up of long, wavy fibers. This wavelike structure guarantees that the loads applied to the Achilles tendon can be absorbed more effectively. This means that under a tensile load this wave shape is initially cancelled out. The collagen in the tendon is then slowly and evenly subject to the load.

Load capacity of the Achilles tendon: the Achilles tendon can withstand very high loads of 500 to 1,000 kg/cm2. It is stronger than a steel cable of the same size and so is the strongest tendon in the body.

The Achilles tendon is full of life: in the tendon tissue, a constant exchange of collagen takes place. Collagen is consistently being formed and broken down.

This exchange is normally very slow, however, in the case of tendon disorders (‘tendinopathies’) it is considerably faster. Collagen is broken down by enzyme processes.

Healthy Achilles tendon: the Achilles tendon is healthy when there is optimum turnover and good circulation. Optimum turnover is achieved, among other things, through movement!

Due to the constant shift between loads being applied and released, the fibers are constantly being compressed, stretched and relaxed. This stimulates the transport of nutrients and waste matter through the Achilles tendon. The inner environment is kept in optimum conditions to guarantee the constant regeneration of tendon tissue.

Nutrition, genes, state of mind and optimum metabolism also have an influence on Achilles tendon health.

5. Blood Circulation

Circulation in the Achilles tendon takes place through four different systems:

  1. A layer of connective tissue, which surrounds the Achilles tendon.
  2. Through vessels running parallel to the Achilles tendon. These branch out into the tendon.
  3. The Achilles tendon is also supplied with blood via the periosteum, a membrane covering the surface of the bones.
  4. Finally, the Achilles tendon is supplied with blood via the bursa or tendon sheath.


At points that are under increased pressure, circulation through the Achilles tendon is considerably worse. This is why chondrocytes may build up in the tendon, leading to complaints.

The Achilles tendon has its own system of vessels that is independent from that of the calf muscle.

Blood Circulation and training:

At rest, the blood circulation through the Achilles tendon is approx. 30–40% of that of the muscle belly. Under load, however, this increases seven-fold and for athletes even more!

During intensive training, above all in the region of the surrounding connective tissue of the Achilles tendon, vasodilatory substances are released, which open up the blood vessels. As this happens, the circulation of the Achilles tendon is increased seven-fold and even more for athletes! The flow of lactic acid and growth hormones, as well as oxygen and glucose, is also increased. Clear signs of increased synthesis activities appear (formation of new, healthy materials)!