Gastrocnemius

legsMusculus gastrocnemius

The gastrocnemius is the visible two-headed calf muscle that gives the lower leg its diamond shape. It crosses the knee as well as the ankle, so it works best with the leg straight.

Gastrocnemius highlighted on an anatomical figure, from behind.
Where it sits, from behind.

The gastrocnemius has two heads, one arising just above each knuckle of the thigh bone at the back of the knee. They run down as two distinct bellies — visible as the two rounded masses at the top of a developed calf — and merge into a broad sheet that joins the soleus beneath it to form the Achilles tendon.

Its main action is pointing the foot downward, which is what pushes you off the ground with each step. It is built for that: it has a high proportion of fast-contracting fibres and is well suited to short, powerful efforts like jumping and sprinting.

It also crosses the knee, which gives it a second action — knee flexion, alongside the hamstrings — and a mechanical consequence that matters more. When the knee is bent, the muscle is already shortened at the top and can produce much less force at the ankle. This is why a seated calf raise barely trains it.

It is the muscle people mean by calf. Its two heads and the shape they produce are most of the visible outline of the back of the lower leg.

Training notes

Standing calf raises are the movement, and the knee must stay straight. Any knee bend transfers the work to the soleus underneath.

It responds to being loaded at long muscle lengths, which means dropping into a full stretch at the bottom of each repetition rather than working in the top half of the range.

It is also loaded by jumping, sprinting and skipping, which suit its fibre composition. Explosive work is a legitimate part of training it, not just a substitute for raises.

The visible split between the two heads is a matter of muscle development and body fat; the height of the calf on the leg is set by where the muscle bellies end, which training does not change.

Anatomy

Origin
  • Medial head: popliteal surface of the femur, above the medial condyle
  • Lateral head: lateral surface of the lateral condyle of the femur
Insertion
  • Posterior surface of the calcaneus, through the calcaneal tendon
Actions
  • Plantarflexes the ankle, pointing the foot downward
  • Flexes the knee
  • Provides the push-off in walking, running and jumping
Innervation
Tibial nerve (S1–S2)

Exercises

Antagonists

Synergists