Soleus

legsMusculus soleus

The soleus is the broad flat calf muscle underneath the gastrocnemius. It does not cross the knee, so it is the muscle that keeps working when the knee is bent.

Soleus highlighted on an anatomical figure, from the front.
Where it sits, from the front.

The soleus is a wide, flat muscle lying beneath the gastrocnemius and extending further down the leg than it does. It arises from the back of both lower leg bones and from a tendinous arch between them, and it joins the gastrocnemius to form the Achilles tendon.

Because it starts below the knee, its length is unaffected by knee position. That makes it the calf muscle that works in every position, and the one that does most of the work whenever the knee is bent.

Its fibre composition is the opposite of the gastrocnemius. The soleus is dominated by slow-contracting, fatigue-resistant fibres, which suits its main job: standing. When you stand still your body constantly tips forward slightly at the ankle, and the soleus contracts continuously to prevent it. It is working right now if you are standing up.

It is also involved in circulation. Contracting it squeezes the deep veins of the calf and pushes blood back toward the heart against gravity, which is why it is sometimes called the second heart or the skeletal muscle pump.

It is larger than the gastrocnemius and contributes more total force at the ankle, despite being the less visible of the two.

Training notes

Seated calf raises are the direct movement, and the bent knee is the whole point — it removes the gastrocnemius and leaves the soleus to do the work.

It is the more commonly neglected calf muscle, since standing raises are the default and they emphasise the gastrocnemius. Given that it is the larger of the two, that is a real omission for anyone trying to build calves.

Its slow-fibre composition means it responds well to higher repetitions, longer time under tension and shorter rests than most muscles.

It is also loaded continuously by walking, standing and carrying, which is part of why calves in general are stubborn — a training stimulus has to exceed a baseline that is already high.

Anatomy

Origin
  • Posterior surface of the head and upper quarter of the shaft of the fibula
  • Soleal line and the middle third of the medial border of the tibia
  • The tendinous arch spanning between the two bones
Insertion
  • Posterior surface of the calcaneus, through the calcaneal tendon
Actions
  • Plantarflexes the ankle at any knee angle
  • Holds the body upright against its tendency to fall forward when standing
  • Assists the return of blood from the leg toward the heart
Innervation
Tibial nerve (S1–S2)

Exercises

Antagonists

Synergists