What is the primary action of the fibularis longus muscle?

• A. Extend tarsus and flex stifle
• B. Flex tarsus and pronate pes
• C. Extend digits II-V
• D. Flex metatarsophalangeal joints

Answer: (B)

The fibularis longus muscle is primarily involved in the movement of the foot and ankle, specifically in facilitating actions that allow for the flexion of the tarsus and pronation of the pes (foot). This muscle originates on the lateral side of the leg and travels down to the foot, where it acts to evert the foot and assist in stabilizing the arch.

When the fibularis longus contracts, it contributes to flexing the tarsus, which enables the foot to point downwards (plantarflexion) and helps with balance and mobility during activities like walking or running. Additionally, the pronation of the pes involves turning the sole of the foot outward, which is important for adapting the foot to various surfaces and movements.