Which muscle is responsible for the plantarflexion of the ankle?

The gastrocnemius muscle is primarily responsible for plantarflexion of the ankle. This action involves pointing the toes downward, which is essential for movements such as walking, running, and jumping. The gastrocnemius is a large muscle located at the back of the lower leg and attaches to the heel through the Achilles tendon. Its positioning and function allow it to effectively control the ankle joint's movement during activities that require pushing off the ground.

Other muscle groups, such as those listed in the other options, have different primary functions. The quadriceps, for instance, are located at the front of the thigh and are responsible for extending the knee rather than affecting ankle movement. The biceps primarily function to flex the elbow and supinate the forearm, while the triceps are involved in extending the elbow. Therefore, the gastrocnemius stands out as the key muscle for ankle plantarflexion due to its specific anatomical role and function.