Calf

Gastrocnemius and soleus form the main bulk of the calf musculature. Gastrocnemius forms the bulky part of the calf and extends from just above the back of your knee to your heel. If you stand on your toes and watch the back of your leg in a mirror, you can see the two parts of gastrocnemius standing out and you can see where they unite to form the Achilles tendon, below the fleshy part of your upper calf. Soleus lies under gastrocnemius and is attached to the back of your leg bones. It feeds in to the Achilles tendon to be attached to your heel. You can see soleus as the fleshy part of your leg on either side of the Achilles tendon. The Achilles tendon itself is extremely thick and strong. It is attached to the middle of the back of your heel and is separated from the upper part of the bone by a bursa, a small sac of fluid, which allows friction-free movement.

Gastrocnemius and soleus contract to pull your heel back and up, when you point your toes down (plantar flexion) or stand on your toes. They create the spring movement when you walk, run, jump and hop. Sprinters have shortened, powerful calf muscles, whereas oarsmen lengthen their calves through the fixed position of their feet in the boat. Gastrocnemius also helps to bend the knee against strong resistance, for instance if you do hamstring curls with heavy weights in weight-training. If your hamstrings are weakened through repeated injury, your gastrocnemius may gain strength to compensate and assist in knee flexion. Soleus does not affect the knee, but is more active as a postural muscle, helping to control the leg over your ankle, against the influence of gravity.