Muscle · Lower leg

Flexor hallucis longus

Musculus flexor hallucis longus

The muscle that drives the big toe into the ground at the end of every step. It starts deep on the back of the outer shin bone, runs behind the inside of the ankle, and threads all the way along the sole to the tip of the great toe. It is the last thing to push before the foot leaves the ground, and it acts like a bowstring running the length of the arch — as it tightens it lifts the arch from underneath. That combination makes it central to push-off power and to how the foot stiffens for propulsion. It is also a well-known source of pain in dancers and runners, where the tendon is squeezed behind the ankle.