Lower LegsSource-checked

Soleus

Pronunciation: SOH-lee-us

For beginners

Hidden beneath the gastrocnemius, this muscle also points your foot down, but because it doesn't cross the knee, it stays active whether your knee is bent or straight — which is why seated calf raises target it more.

Show the advanced explanation

Composed of a higher proportion of slow-twitch (fatigue-resistant) fibers than the gastrocnemius, the soleus is well-suited to its role in constant postural micro-adjustments during standing.

Structure & function

Location: A broad, flat muscle lying deep beneath the gastrocnemius, visible along the sides of the lower calf.
Origin: Back of the tibia and fibula (below the knee).
Insertion: Calcaneus (heel bone), via the Achilles tendon (shared with the gastrocnemius).
Main action(s): Plantarflexes the ankle; unlike the gastrocnemius, it does not cross the knee, so its contribution does not change with knee position.
Joint(s) crossed: Ankle joint only
Movement plane: sagittal
Innervation: Tibial nerve (S1–S2)
In daily movement: Maintaining standing balance by making small, constant adjustments at the ankle, and assisting push-off while walking.
In exercise: Prime mover of ankle plantarflexion in seated calf raises, where the bent knee slackens the gastrocnemius and shifts more demand to the soleus.
Commonly confused with: Frequently lumped together with the gastrocnemius as 'the calf,' but training them optimally uses different knee positions (straight vs. bent).
Common misconceptions: 'Calf raises are all the same regardless of knee position' is incorrect — knee angle meaningfully shifts the emphasis between the gastrocnemius and soleus.

Exercises that use this muscle

As a primary mover

Seated Calf Raise

As a secondary / stabilizer

Standing Calf Raise (secondary)

⚠ Safety note

Similar precautions to the gastrocnemius; sharp calf pain or a pop needs assessment.

Sources

“The soleus plantarflexes the ankle and, unlike the gastrocnemius, does not cross the knee joint.”

Anatomy and Physiology 2e — OpenStax, Rice University · Ch. 11.6 Appendicular Muscles of the Pelvic Girdle and Lower Limbs

Peer-reviewed textbook · License: CC BY-NC-SA 4.0 · Last checked 2026-07-19

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