ACSM Personal Trainer Certification Practice Exam

Which muscle is mainly responsible for plantarflexion at the ankle joint?

1. Soleus

2. Gastrocnemius

3. Tibialis anterior

4. Peroneus tertius

The correct answer is: Gastrocnemius

The muscle primarily responsible for plantarflexion at the ankle joint is the gastrocnemius. Plantarflexion is the movement that points the toes downward, which is essential for actions such as standing on tiptoe, pushing off during walking or running, and many other activities involving the feet. The gastrocnemius, a large muscle located in the back of the lower leg, has two distinct heads that originate from the femur. Its primary action is to aid in plantarflexion of the ankle when the knee is extended, and it also plays a role in knee flexion. Because of its size and position, the gastrocnemius is a significant contributor to producing force during activities that involve rising on the toes or propelling the body forward. The soleus, while also involved in plantarflexion, primarily functions when the knee is flexed and is considered a more stable muscle for maintaining posture and balance. The tibialis anterior is primarily responsible for dorsiflexion, the opposite movement where the toes are lifted upwards. The peroneus tertius assists with dorsiflexion and eversion of the foot. Thus, the gastrocnemius is specifically recognized for its substantial contribution to plantarflexion, particularly during dynamic movements