Which muscle primarily plantarflexes the foot at the ankle joint?

• A. Tibialis anterior
• B. Fibularis (peroneus) tertius
• C. Gastrocnemius
• D. Extensor digitorum longus

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the action of plantarflexion, which is the movement that points the foot downward away from the leg, like pressing a gas pedal.
2. Step 2: Identify the muscles listed and their primary functions: Tibialis anterior dorsiflexes the foot (pulls it upward), Fibularis (peroneus) tertius assists in dorsiflexion and eversion, Extensor digitorum longus extends the toes and dorsiflexes the foot.
3. Step 3: Recognize that the Gastrocnemius muscle, located in the calf, crosses the ankle joint posteriorly and is a powerful plantarflexor of the foot.
4. Step 4: Recall that the Gastrocnemius works together with the Soleus muscle to perform plantarflexion, which is essential for movements like standing on tiptoes and pushing off during walking or running.
5. Step 5: Conclude that among the options, the Gastrocnemius is the primary muscle responsible for plantarflexion at the ankle joint.