Which movement will shorten the fibers of the tibialis anterior?

• A. Dorsiflexion
• B. Plantar Flexion
• C. Inversion
• D. Eversion

Answer: (A)

The primary action that shortens the tibialis anterior fibers is dorsiflexion of the foot. This muscle runs along the front of the shin and contracts to lift the foot upward toward the shin, bringing the ankle into dorsiflexion. When it does this, the muscle fibers shorten as they pull on the foot, producing that movement.

Plantarflexion lengthens the muscle because it moves the foot downward, opposite to the tibialis anterior’s action, so the fibers are stretched rather than shortened. Inversion and eversion involve subtalar movements and other muscles; while the tibialis anterior can assist with inversion, its shortening is most directly tied to dorsiflexion.