ACSM Personal Trainer Certification Practice Exam

Which joint motion is the peroneus tertius responsible for at the ankle?

1. Plantarflexion

2. Dorsiflexion

3. Inversion

4. Adduction

The correct answer is: Dorsiflexion

The peroneus tertius is primarily responsible for dorsiflexion at the ankle joint. This muscle is located on the anterior aspect of the lower leg and, while it also plays a role in eversion of the foot, its main function is to lift the foot upwards in the dorsiflexion movement. Dorsiflexion occurs when the toes are brought closer to the shin, allowing for movements such as walking on the heels or lifting the toes during gait. Understanding this motion is vital for personal trainers when developing programs that include lower extremity movements or rehabilitative exercises. In contrast, plantarflexion would involve pointing the toes down, which is primarily achieved by other muscles, such as the gastrocnemius and soleus. Eversion refers to turning the sole of the foot outward, which is a secondary function of the peroneus tertius, but not its primary role. Adduction of the foot is not associated with any significant muscle action at the ankle joint and is instead a movement more related to the hip joint. Therefore, the peroneus tertius’s contribution to dorsiflexion is crucial for various functional activities and movements.