Which two muscles are the primary plantarflexors of the foot?

• A. Gastrocnemius and Soleus
• B. Tibialis anterior and Extensor digitorum longus
• C. Peroneus longus and Peroneus brevis
• D. Plantaris and Flexor digitorum longus

Answer: (A)

The main action being tested is which muscles powerfully push the foot down at the ankle, i.e., plantarflexion. The best answer is the pair known as the triceps surae: the gastrocnemius and the soleus. These two muscles merge into the Achilles tendon and attach to the heel, providing most of the force needed to plantarflex the ankle, especially during standing on tiptoe or push-off in walking. The gastrocnemius crosses both the knee and ankle, so it contributes strongly when the knee is straight, while the soleus lies under it and remains a primary plantarflexor regardless of knee position.

Other muscles listed don’t serve as the main plantarflexors. The tibialis anterior and extensor digitorum longus are located on the front of the leg and are primary dorsiflexors, not plantarflexors. The peroneus longus and brevis mainly evert the foot and contribute only modestly to plantarflexion. The plantaris and flexor digitorum longus can assist, but they’re not the primary ankle plantarflexors.