Gastrocnemius

What it is

The superficial calf muscle, and the one you can see: two prominent bellies forming the diamond shape at the back of the lower leg. Gaster kneme is Greek for the belly of the leg.

Its two heads arise from the back of the femur, above the knee joint, and descend to merge with soleus into the calcaneal tendon. The medial head is usually the larger and hangs lower, which is why most people's calves are visibly asymmetrical from behind.

It is composed of a relatively high proportion of fast-contracting fibres compared with soleus underneath it — a difference that reflects their different jobs rather than their potential.

What it does

Plantarflexes the ankle and flexes the knee. Crossing two joints is the defining fact about it.

Because it crosses the knee, its length depends on knee position. Bend the knee and it slackens, losing most of its ability to contribute at the ankle. Straighten the knee and it is at a working length and contributes powerfully.

This is why a seated calf raise trains soleus and a standing one trains both. It is also why your calf cramps more readily with a straight leg and pointed toes — the muscle is at its shortest across both joints at once.

What loads it

Standing calf raises, jumping, sprinting, and push-off with a relatively straight knee. Walking uphill.

The calf raise is the direct one — and the straight-knee version specifically, for the reason given above.

What is commonly got wrong about it

That calf size is a matter of training effort. Calf muscle bellies vary enormously in length between people, and where the muscle ends and the tendon begins is anatomy you were born with. A short muscle belly on a long tendon will never look like a long belly on a short tendon, however it is trained. This is one of the clearest cases in the body where the shape ceiling is structural — and it is also a good illustration of why this site does not treat appearance as a training goal.

That high reps are required because the calf is "endurance". The fibre-type difference between gastrocnemius and soleus is real, but the rep-range prescription built on top of it is a much bigger claim than the underlying observation supports.

Confusing it with the Achilles tendon. The muscle is what contracts; the tendon transmits it.