Gastrocnemius

A very powerful superficial muscle that is in the back part of the lower leg and also called the calf. It runs from its two heads just above the knee to the heel, and is involved in standing, walking, running and jumping. Along with the soleus muscle it forms the calf muscle. Its function is plantar flexing the foot at the ankle joint and flexing the leg at the knee joint.

The gastrocnemius muscle is very prone to spasms; the painful, involuntary, contraction of the muscle for up to several minutes