Gastrocnemius Muscle Anatomy

Location & Overview

The gastrocnemius muscle is an essential muscle in the lower leg responsible for walking and maintaining posture. It is composed of two heads: the medial and lateral heads. The medial head is thicker and wider than the lateral head. These two heads originate from the lateral and medial condyles of the femur and, when combined with the soleus muscle, form what is commonly known as the ‘calf muscle’. The technical term for this group of muscles is the triceps surae, which also includes the plantaris muscle. Together, these three muscles make up the superficial flexor group of the lower leg, with the gastrocnemius as the most superficial, or closest to the surface of the skin.^[1,2,3]

The aponeurosis of the gastrocnemius muscle attaches to the calcaneal tendon, which is more commonly known as the Achilles tendon. This is the longest and widest tendon in the human body, and it derives its name from Achilles, a character in Greek mythology. According to the myth, Achilles’ entire body was invulnerable, except for his calcaneal tendon, which became his weakness. This is the origin of the phrase “Achilles heel,” which refers to a weakness in spite of overall strength.^[1,3]

Origin & Insertion

The gastrocnemius muscle has two heads that originate from the lateral and medial condyles of the femur, with its origin also crossing onto the popliteal surface of the femur. The popliteal surface of the femur is a smooth triangular bony area on the posterior distal femur, bounded by the medial and lateral supracondylar lines and inferiorly by the intercondylar line. As the gastrocnemius muscle extends downward, the two heads converge and form a large aponeurosis that attaches to the calcaneal tendon. The calcaneal tendon, in turn, inserts onto the posterior surface of the calcaneus, or heel bone.^[3,4]

Action & Function

The primary action of the gastrocnemius muscle is to cause plantar flexion of the foot at the ankle joint, which is commonly used during activities such as walking, running, and jumping, especially during activities that require push-off forces at the ankle joint. It works in conjunction with the soleus muscle as part of the triceps surae group to achieve this action. The plantaris muscle can also weakly contribute to plantar flexion. In addition, the gastrocnemius contributes to maintaining postural stability and balance while standing, as it helps resist the force of gravity and prevents the body from falling forward.^[1,3]

A secondary action of the gastrocnemius muscle is to cause flexion of the leg at the knee joint. However, the gastrocnemius muscle is not capable of exerting its full power when flexing the knee and plantar flexing the ankle simultaneously. Rather, it is most effective when performing its actions separately.^[1,1,3] The hamstring muscles are primarily responsible for flexing the knee joint and are composed of the semitendinosus, semimembranosus, and biceps femoris muscles.^[5]

Innervation

The gastrocnemius is innervated by the tibial nerve (S1-S2). The tibial nerve is a branch of the sciatic nerve. The tibial nerve also innervates the calf muscles and the plantaris.^[3,1]

Blood Supply

Blood is supplied to the gastrocnemius via the sural arteries. The sural arteries are collateral arteries of the popliteal artery, which is derived from the femoral artery.^[1]