The gastrocnemius muscle is a muscle of the superficial group of the posterior muscles of the calf, and it runs from the knee to heel.
Location
The gastrocnemius muscle is part of the triceps surae (three-headed calf muscle), which is created from gastrocnemius and soleus muscle. Both of these muscles are strong and big, especially well formed in humans.
Structure
Gastrocnemius arises by two heads – medial and lateral, which are connected with two condyles of the femur by two strong tendons. Together with soleus, gastrocnemius ends in the calcaneal tendon.
Anatomy
The medial head is larger, and it takes its origin from a depression in upper back part of medial condyle, lower parts of the posterior side of the femur and posterior side of the capsule of the knee. The lateral head arises from side of the lateral condyle, lower parts of the posterior surface of the femur, immediately above the side of the condyle, and posterior surface of the knee capsule.
Tendons that start from femoral condyles spread out in aponeuroses, which cover the posterior portion of the muscular head to which it belongs. From the anterior surface of aponeuroses, the muscular fibers are given of.
Fibers of the medial head are thicker and extend lower than those of the lateral one. All the fibers are united at an angle, in the medial line of the muscle in the tendinous raphe, which expands in broad aponeurosis on the anterior surface of the muscle.
The posterior surface of this anteriorly placed aponeurosis is a place from which remaining muscle fibers are given of. The aponeuroses are gradually contracting and, together with the tendon of the soleus muscle, create calcaneal tendon.
Calcaneal tendon inserts in the lower parts of the posterior side of the heel bone (calcaneus) in the surface elevation called tuberositas of calcaneus. This tendon is also called Achilles tendon or heel cord, and it is the strongest and thickest tendon in the human body.
Innervation for gastrocnemius muscle comes from first and second sacral nerves, through the tibial nerve.
Function
Together with soleus muscle, gastrocnemius generates as much as 93% of the plantar flexion force. The main function is elevating the heel and depressing the forefoot (standing on fingers).
Most of the gastrocnemius fibers are white, fast twitched (type 2) variety. Contractions of these muscle fibers produce rapid movement during jumping and running. The gastrocnemius is only intermittently in action during the symmetrical standing. It is said that we jump with gastrocnemius and walk with soleus.
The gastrocnemius muscle can act on both knee and the ankle joints, however, it cannot exert its full power on both joints at the same time. It is most effective when the knee is extended, and it is maximally activated when knee extension is combined with dorsiflexion, as it happens in sprint start.
Together with soleus, gastrocnemius is important for circulation of venous blood, providing the return of the blood from superficial to deep veins and also superiorly to larger vessels to the heart.
Clinical significance
Tennis leg is a painful injury caused by partial rupture of the muscle fibers of the medial head of the gastrocnemius muscle, near the beginning of its tendon. It occurs when there is an overextension of the muscle with knee extension and dorsiflexion of the foot. Most often, this injury happens in middle-aged tennis players, while they serve the ball or overextend to catch the ball. Usually, there is an abrupt onset of stabbing pain, followed by edema and spasm of the gastrocnemius.
The gastrocnemius is one of the rare muscles that get their blood supply from only one artery (sural artery, branch of popliteal artery). They are terminal arteries, which means that their breakage or occlusion results in necrosis in corresponding muscle tissue.
Near the proximal attachment, the lateral head of gastrocnemius may contain a sesamoid bone, fabella, which articulates with lateral femoral condyle and is visible on lateral radiographs of the knee.
In some cases, the third head of gastrocnemius can be noted, so-called Gastrocnemius Tertius of Kelch, may arise from popliteal surface of the femur. Sometimes, it can cross popliteal neurovascular structures and has been shown to cause clinical problems, such as intermittent claudication, arterial stasis, and aneurysm (popliteal vascular entrapment syndrome), venous stasis and nerve impairment. It happens in around 5% of cases.
This muscle is also prone to painful spasms, which are involuntary contractions that can last few minutes and are usually connected poor circulation, fatigue, and some electrolyte imbalances. Gastrocnemius can become inflamed, and it usually happens in cases of overuse during physical activity.
