Which muscle is the prime mover of dorsiflexion at the ankle joint?

• A. Tibialis anterior
• B. Gastrocnemius
• C. Fibularis longus
• D. Soleus

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the term 'prime mover' in the context of muscle actions. The prime mover, also known as the agonist, is the muscle primarily responsible for producing a specific movement.
2. Step 2: Define 'dorsiflexion.' Dorsiflexion is the movement that decreases the angle between the dorsum (top) of the foot and the shin, effectively lifting the foot upward at the ankle joint.
3. Step 3: Review the anatomy of the muscles listed in the options: Tibialis anterior, Gastrocnemius, Fibularis longus, and Soleus. Identify which muscle is anatomically positioned to perform dorsiflexion.
4. Step 4: Analyze the function of each muscle: The Tibialis anterior is located on the anterior (front) side of the leg and is primarily responsible for dorsiflexion. The Gastrocnemius and Soleus are located on the posterior (back) side of the leg and are involved in plantarflexion (pointing the foot downward). The Fibularis longus contributes to eversion and plantarflexion, not dorsiflexion.
5. Step 5: Conclude that the Tibialis anterior is the prime mover for dorsiflexion at the ankle joint based on its anatomical position and primary function.