Gastrocnemius muscle the medial condyle of the femur. Its other end forms a common tendon with the soleus muscle; this tendon is known as the calcaneal tendon or Achilles Tendon and inserts onto the posterior surface of the calcaneus, or heel bone. Further, it is considered a superficial muscle as it is located directly under skin, so its shape is clearly visible in a normal human being. Deep to the gastrocnemius (farther from the skin) is the soleus muscle. Some anatomists consider both to be a single muscle, the triceps surae or "three-headed [muscle] of the calf", since they share a common
Anatomical terms of muscle need antagonistic pairs located in opposite sides of a joint or bone, including abductor-adductor pairs and flexor-extensor pairs. These consist of an extensor muscle, which "opens" the joint (by increasing the angle between the two bones) and a flexor muscle, which does the opposite by decreasing the angle between two bones. However muscles don't always work this way - sometimes agonists and antagonists contract at the same time to produce force, as per Lombard's paradox. Also, sometimes during a joint action controlled by an agonist muscle (see above definition of agonist), the antagonist will be slightly activated, naturally. This occurs