Posterior Leg: Superficial
- Gastrocnemius and Soleus (both S1, S2)
- Both muscles provide foot plantar flexion: we test gastrocnemius with the knee extended and soleus with the knee flexed.
Posterior Leg: Deep
- Tibialis posterior and flexor digitorum longus and flexor hallucis longus (all L5, S1).
- Note that some texts indicate that L4 also innervates tibialis posterior and some texts indicate that S2 also innervates the flexor digitorum and hallucis muscles.
- Tibialis posterior provides foot inversion.
- Flexor digitorum longus flexes the toes (except the great toe).
- Flexor hallucis longus flexes the great toe.
Lesser muscles
- Popliteus & Plantaris.
- Popliteus unlocks the knee at the beginning of knee flexion.
- Plantaris acts in concert with gastrocnemius.
Foot
- The plantar nerves innervate the plantar intrinsic foot muscles (S1 – S3).
Sensory innervation
- The tibial nerve produces the medial sural cutaneous nerve, which joins the sural communicating branch to form the sural nerve.
- When the sural nerve passes through the ankle, it produces both the lateral calcaneal nerve branch and also the lateral dorsal cutaneous nerve.
- The lateral calcaneal branch is the lateral corollary of the medial calcaneal branch (see below).
- Within the tarsal tunnel, the tibial nerve divides into the plantar nerves (medial and lateral) and also the medial calcaneal sensory nerve.