The lower leg muscles move the ankle and toes and push the body forward with each step. Tight fascia divides them into four compartments, each with its own nerve and blood supply.
Calf
The gastrocnemius and soleus join in the Achilles tendon to point the foot down (plantar flexion). They lift the heel when walking and are supplied by the tibial nerve.
Front of the leg
The tibialis anterior and toe extensors lift the foot (dorsiflexion) and are supplied by the deep peroneal (fibular) nerve. Weakness causes foot drop and a high-stepping gait.
Side of the leg
The peroneus (fibularis) longus and brevis turn the sole outward (eversion) and support the ankle. They are supplied by the superficial peroneal nerve.
Foot
Small intrinsic muscles and the plantar fascia support the arches and steady the toes. Nerve damage, as in diabetes, weakens them and leads to deformity and pressure points.
| Compartment | Main action | Nerve |
|---|---|---|
| Anterior | Dorsiflexion, toe extension | Deep peroneal |
| Lateral | Eversion | Superficial peroneal |
| Superficial posterior | Plantar flexion | Tibial |
| Deep posterior | Toe flexion, inversion | Tibial |
At the bedside
After a leg fracture or crush injury, pain out of proportion and pain on passive stretch of the toes suggest compartment syndrome, a surgical emergency. In the Thompson test, squeezing the calf without foot movement points to an Achilles tendon rupture.
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Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).