Which combination of muscles is primarily responsible for ankle plantarflexion?

• A. Tibialis posterior
• B. Flexor digitorum longus
• C. Tibialis anterior
• D. Gastrocnemius and soleus

Answer: (D)

Ankle plantarflexion is driven mostly by the muscles of the back of the leg—the gastrocnemius and the soleus—together known as the triceps surae. When they contract, they pull on the Achilles tendon and raise the heel, pointing the toes downward. The gastrocnemius crosses both the knee and the ankle, so knee position can influence its contribution, but the soleus crosses only the ankle and provides a steady, powerful plantarflexion, especially during standing and push-off. Because they work in tandem, they produce the strongest plantarflexion torque compared with other muscles.

Tibialis posterior can assist in plantarflexion, but its main role is more about foot stability and arch support. Flexor digitorum longus helps flex the toes and can assist in plantarflexion, but it’s not the primary ankle plantarflexor. Tibialis anterior does the opposite—dorsiflexes the ankle (and inverts the foot)—so it does not contribute to plantarflexion.