Muscle Group: Gastrocnemius is largest and most superficial of the two calf muscles. Forms part of a composite muscle known as the triceps surae (with the soleus and plantaris muscles)
Action: Plantarflexes the ankle joint (points toes downwards), flexes the knee
Origin: Medial and lateral femoral condyles, knee joint capsule and oblique popliteal ligament
Insertion: Posterior surface of the calcaneus via the tendocalcaneus (aka Achilles tendon)
Nerve Supply: Tibial Nerve (S1, S2)
Functional Activities: Standing on tip toes, provides the main propulsive force with walking, running and jumping
Gastrocnemius is the muscle that forms the main bulk of the calf region on the back of the lower leg. It is a bipennate muscle, meaning it has two rows of muscle fibres, facing in opposite directions with a central tendon, resembling a feather. The shape allows for greater power. The muscle runs from just above the knee to the heel bone, thereby crossing two joints, so it acts on both the knee and ankle joint.
It has two heads which arise from the medial and lateral femoral condyles, just above the knee joint. The medial head arises from behind the medial supracondylar ridge and the adductor tubercle on the popliteal surface of the femur (thigh bone). The lateral head arises from the outer surface of the lateral femoral condyle, just above and behind the lateral epicondyle. Both heads also have an additional attachment from the knee joint capsule and from the oblique popliteal ligament.
A fleshy bulk of muscle fibres arise from each head and gradually come together (without blending), inserting into the posterior surface of a broad membranous tendon which fuses with the soleus tendon to form the upper part of the tendocalcaneus, more commonly referred to as the Achilles tendon. This broad tendon gradually narrows and becomes more rounded until it reaches approximately 4cm above the calcaneus (heel bone) where it expands again until it inserts to the middle part of the posterior surface of the calcaneus.
Together with the soleus and plantaris muscles, gastrocnemius forms a composite muscle known as the triceps surae, one of the most powerful groups of muscle in the body. The three muscles work together to plantarflex the ankle joint i.e. pull the foot downwards. Gastrocnemius provides a majority of the propulsive force during running, walking and jumping. It is predominantly made up of type II fast twitch fibres (white muscle fibres) so is primarily involved in fast, powerful movements rather than more passive or stabilising control.
As the muscle arises above the knee, it can also flex the knee joint. However if it works over both joints simultaneously, it cannot exert full power over both joints e.g. it has more strength to flex the ankle joint if the knee is straight rather than bent.
Common problems that arise in gastrocnemius include:
1) Tightness: frequent wearing of high heels often results in shortening of the muscle which can limit dorsiflexion and make it difficult to walk barefoot or in flat shoes
2) Cramp: Spasms, involuntary, painful contractions may affect gastrocnemius, lasting anywhere from a few seconds to a few minutes
3) Calf Strain/Tear: If the muscle is suddenly overstretched, or repetitively overused, some or all of the muscle fibres may be torn
Here are some other topics that may be of interest:
1) Calf Stretches: Simple and effective ways to stretch the calf muscles
2) Calf Strengthening: Loads of great exercises for strengthening the calf muscles - choose from beginners, intermediate or advanced level
3) Achilles Tendonitis: Inflammation and degeneration of the achilles tendon is a common problem - find out about the causes, symptoms and treatment options