CorpusHuman Anatomy
MuscularMuscle

Gastrocnemius

Musculus gastrocnemius

Also known as: calf muscle, triceps surae, gastrocs

The most superficial calf muscle, with two heads from the femoral condyles. It joins soleus in the calcaneal tendon. It powerfully plantarflexes the ankle and flexes the knee, giving the push-off in walking, running and jumping.

Show on body map Muscles — Posterior View

Overview

The medial head arises from the popliteal surface of the femur above the medial condyle. The smaller lateral head arises from the lateral surface of the lateral condyle, often containing a sesamoid bone, the fabella. The two heads form the inferior borders of the popliteal fossa and unite into a broad aponeurosis that fuses with the soleus tendon to form the calcaneal (Achilles) tendon. Together with soleus (and plantaris) it forms the triceps surae.

Gastrocnemius is rich in fast (type II) fibres. It provides rapid, powerful plantarflexion in running, jumping and the push-off phase of gait. Because it crosses the knee, it also flexes the knee, and it cannot fully plantarflex when the knee is fully flexed (it becomes actively insufficient). It is supplied by the tibial nerve (S1–S2). The ankle jerk tests S1.

Location

Superficial posterior compartment of the leg (the "calf").

Parts & subdivisions

  1. Medial head
    Larger. From the femur above the medial condyle. Commonly strained ("tennis leg").
  2. Lateral head
    From the lateral femoral condyle. May contain the fabella.

Anatomy

Origin

Medial head: popliteal surface of the femur above the medial condyle. Lateral head: lateral surface of the lateral femoral condyle.

Insertion

Posterior surface of the calcaneus via the calcaneal tendon.

Action

Plantarflexion of the ankle when the knee is extended; flexion of the knee; raises the heel during walking.

Innervation

Tibial nerve.

Nerve roots

S1–S2

Arterial supply

Sural arteries (from the popliteal artery).

Relations

Covers soleus and plantaris. Its heads form the lower borders of the popliteal fossa. The small saphenous vein and the sural nerve run in the groove between the heads.

Function

  • Plantarflexes the ankle (push-off, jumping)
  • Flexes the knee
  • Raises the heel in walking

Clinical significance

"Tennis leg"

Sudden pain in the mid-calf during a lunge or push-off in middle-aged sportspeople, caused by tearing of the medial head at its musculotendinous junction. It can mimic deep vein thrombosis.

Ankle reflex

Tapping the calcaneal tendon with the foot slightly dorsiflexed produces plantarflexion (S1, tibial nerve). It is reduced in S1 radiculopathy and peripheral neuropathy and delayed in hypothyroidism.

Gastrocnemius tightness

Limited ankle dorsiflexion with the knee extended but not with the knee flexed (Silfverskiöld test) points to an isolated gastrocnemius contracture, as in cerebral palsy or plantar fasciitis.

Mnemonics

Ankle jerk

"S1–2, buckle my shoe."

Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.