Final answer:
The gastrocnemius, commonly known as the calf muscle, when contracted, causes plantar flexion of the foot. It is joined by the soleus muscle in enabling this movement, both of which are critical for standing and walking.
Step-by-step explanation:
The muscle responsible for flexing the foot, commonly referred to as the calf muscle, is the gastrocnemius. This muscle, along with the soleus and occasionally the plantaris, insert onto the calcaneal tendon (Achilles tendon) and are found in the superficial posterior compartment of the leg.
When the gastrocnemius contracts, it causes plantar flexion at the ankle, which means it pulls the heel up, allowing you to stand on your toes. The soleus lies deep to the gastrocnemius and also aids in plantar flexion. Both of these muscles are crucial for standing upright, walking, and running.
It's worth noting that while the gastrocnemius and soleus are the primary muscles for plantar flexion, there are other muscles in the leg, such as the fibularis longus and fibularis brevis (also known as peroneus longus and brevis), which also contribute to the plantar flexion and eversion of the foot at the intertarsal joints.